On the evening of the 16th ult., Mr. A. Reckenzaun read a paper on "Electric Launches," before the members of the Society of Arts. At the meeting of the British Association in Southport, last year, Mr. Reckenzaun gave a similar paper, which was published in the Electrical Review at the time. In his present lecture the author does not advance anything new, but treats the subject in a wider sense. We shall therefore only give the more important points brought forward by Mr. Reckenzaun. In speaking of the convenience of electrically-propelled vessels, the lecturer says :-
Nearly the whole space of a launch should be available for the accommodation of passengers, and this is the case with an electrically-propelled launch. We have it on good authority, that an electric launch will accommodate nearly double the number of passengers that a steam launch of the same dimensions would.
A further convenience arising from electromotive power is the absence of combustibles, and the absence of the products of combustion - matters of great importance; and for the milder seasons, when inland navigation is principally enjoyed, the absence of heat, smell, and noise, and, finally, the dispensing with one attendant on board, whose wages, in most cases, amount to as much or more than the cost of fuel, besides the inconvenience of carrying an additional individual. (Mr. Reckenzaun then goes on to describe Jacobi's apparatus, which was employed 45 years ago on the river Neva, and with which our readers are already acquainted.)
It may not be generally known that an electric launch was tried for experimental purposes on a lake at Penllegaer, near Swansea. Mr. Robert Hunt, in the discussion of his paper on electro-magnetism before the Institution of Civil Engineers in 1858, mentioned that he carried on an extended series of experiments at Falmouth, and at the instigation of Benkhausen, Russian Consul-General, he communicated with Jacobi upon the subject. In the year 1848, at a meeting of the British Association at Swansea, Mr. Hunt was applied to by some gentlemen connected with the copper trade of that part, to make some experiments on the electrical propulsion of vessels; they stated, that although electricity might cost thirty times as much as the power obtained from coal, it would, nevertheless, be sufficiently economical to induce its employment for the auxiliary screw ships employed in the copper trade with South America.
The boat at Swansea was partly made under Mr. (now Sir William) Grove's directions, and the engine was worked on the principle of the old toys of Ritchie, which consisted of six radiating poles projecting from a spindle, and rotating between a large electro-magnet. Three persons travelled in Hunt's boat, at the rate of three miles per hour. Eight large Grove's cells were employed, but the expense put it out of question as a practical application.
Professor Silvanus Thompson says that an electric boat was constructed by Mr. G. E. Dering, in the year 1856, at Messrs. Searle's yard, on the river Thames; it was worked by a motor in which rotation was effected by magnets arranged within coils, like galvanometer needles, and acted on successively by currents from a battery.
From a recent number of the Annales de l'Electricite, we learn that Count de Moulins experimented on the lake in the Bois de Boulogne, in the year 1866, with an iron flat-bottomed boat, carrying twelve persons. Twenty Bunsen cells furnished the current to a motor on Froment's principle turning a pair of paddle wheels.
Until Trouve's trip on the Seine, in 1881, and the launch of the Electricity on the Thames, in 1882, very little was known concerning the history of electric navigation.
M. Trouve originally employed Plante's secondary battery, but afterwards reverted to a bichromate battery of his own invention. In all the primary batteries hitherto applied with advantage, zinc has been used as the acting material. Where much power is required, the consumption of zinc amounts to a formidable item; it costs, in quantity, about 3d. per pound, and in a well-arranged battery a definite quantity of zinc is transformed. The final effect of this transformation manifests itself in electrical energy, amounting to about 746 Watts, or one electrical horse-power for every two pounds of this metal consumed per hour. The cost of the exciting fluid varies, however considerably; it may be a solution of salts, or it may be dilute acid. Considering the zinc by itself, the expense for five electrical or four mechanical horse-power through an efficient motor, in a small launch, would be 2s. 6d. per hour. Many persons would willingly sacrifice 2s. 6d. per hour for the convenience, but a great item connected with the employment of zinc batteries is in the exciting fluid, and the trouble of preparing the zinc plates frequently. The process of cleaning, amalgamating and re-filling is so tedious, that the use of primary batteries for locomotive purposes is extremely limited. To re-charge a Bunsen, Grove, or bichromate battery, capable of giving six or seven hours' work at the rate of five electrical horsepower, would involve a good day's work for one man; no doubt he would consider himself entitled to a full day's wages, with the best appliances to assist him in the operation.
Several improved primary batteries have recently been brought out, which promise economical results. If the residual compound of zinc can be utilised and sold at a good price, then the cost of such motive-power may be reduced in proportion to the value of those by-products.
For the purpose of comparison, let us now employ the man who would otherwise clean and prepare the primary cells, at engine-driving. We let him attend to a 6 horse-power steam-engine, boiler, and dynamo machine for charging 50 accumulators, each of a capacity of 370 ampere hours, or one horse-power hour. The consumption of fuel will probably amount to 40 lbs. per hour, which, at the rate of 18s. a ton, will give an expenditure of nearly 4d. per hour. The energy derived from coal in the accumulator costs, in the case of a supply of 5 electrical horsepower for 7 hours, 2s. 9d.; the energy derived from the zinc in a primary battery, supplying 5 electrical horse-power for 7 hours, would cost 17s. 3d.
In order that electric launches may prove useful, it will be desirable that charging stations should be established, and on many of the British and Irish rivers and lakes there is abundance of motive power, in the shape of steam or gas-engines, or even waterwheels.
A system of hiring accumulators ready for use may, perhaps, best satisfy the conditions imposed in the case of pleasure launches.
It is difficult to compile comparative tables showing the relative expenses for running steam launches, electric launches with secondary batteries, and electric launches with primary zinc batteries; but I have roughly calculated that, for a launch having accommodation for a definite number of passengers, the total costs are as 1, 2.5, and 12 respectively, steam being lowest and zinc batteries highest.
The accumulators are, in this case, charged by a small high-pressure steam-engine, and a very large margin for depreciation and interest on plant is added. The launch taken for this comparison must run during 2,000 hours in the year, and be principally employed in a regular passenger service, police and harbour duties, postal service on the lakes and rivers of foreign countries, and the like.
A complete Faure-Sellon-Volckmar cell, such as is used in the existing electric launches, weighs, when ready for use, 56 lbs.; and it stores energy equal to 1 horse-power for 1 hour - 1,980,000 foot-pounds, or about 1 horse-power per minute for each pound weight of material. It is not advantageous to withdraw the whole amount of energy put in; although its charging capacity is as much as 370 ampere hours, we do not use more than 80 per cent., or 300 ampere hours; hence, if we discharge these accumulators at the rate of 40 amperes, we obtain an almost constant current for 7 1/2 hours; one cell gives an E.M.F. of 2 volts. In order to have a constant power of 1 horse for 7 1/2 hours, at the rate of 40 amperes discharge, we must have more than 9 cells per electrical horse-power; and 47 such cells will supply 5 electrical horse power for the time stated, and these 47 cells will weigh 2,632 lbs.
We could employ half the number of cells by using them at the rate of 80 amperes, but then they will supply the power for less than half the time. The fact, however, that the cells will give so high a rate of discharge for a few hours, is, in itself, important, since we are enabled to apply great power if desirable; the 47 cells above referred to can be made to give 10 or 12 electrical horse-power for over two hours, and thus propel the boat at a very high speed, provided that the motor is adapted to utilise such powerful currents.
The above-mentioned weight of battery power - viz., 2,632 lbs., to which has to be added the weight of the motor and the various fittings—represents, in the case of a steam launch, the weight of coals, steam-boiler, engine, and fittings. The electro-motor capable of giving 4 horse-power on the screw shaft need not weigh 400 lbs. if economically designed; this, added to the weight of the accumulators, and allowing a margin for switches and leads, brings the whole apparatus up to about 28 cwt.
An equally powerful launch engine and boiler, together with a maximum stowage of fuel, will weigh about the same. There is, however, this disadvantage about the steam power, that it occupies the most valuable part of the vessel, taking away some eight or nine feet of the widest and most convenient part, and in a launch of 24 feet length, requiring such a power as we have been discussing, this is actually one third of the total length of the vessel, and one-half of the passenger accommodation; therefore, I may safely assert that an electric launch will carry about twice as many people as a steam launch of similar dimensions.
The drawing, fig. 1, represents an electric launch built by Messrs. Yarrow and Company, and fitted up by the Electrical Power Storage Company, for the recent Electrical Exhibition in Vienna. She made a great number of successful voyages on the river Danube during the autumn. Her hull is of steel, 40 feet long and 6 feet beam, and there are seats to accommodate 40 adults comfortably. Her accumulators are stowed away under the floor, so is the motor, but owing to the lines of the boat, the floor just above the motor is raised a few inches. This motor is a Siemens D2 machine, capable of working up to 7 horse-power with 80 accumulators.
In speaking of the horse-power of an electro-motor, I always mean the actual power developed on the shaft, and not the electrical horse-power; this, therefore, should not be compared to the indicated horse-power of a steam-engine.
Comparing the relative weights of the steam-power and the electric-power for this launch, we find that they are nearly equal, each approaches 50 cwt.; but in the case of the steam launch we include 10 cwt. of coals, which can be stowed into the bunkers, and which allow fifteen hours' continuous steaming, whereas the electric energy stored up will only give us seven and a-half hours with perfect safety.
I have here allowed 8 lbs. of coal per indicated horse-power per hour, and 10 horse-power giving off 7 mechanical horse-power on the screw shaft; this is an example of an average launch engine. There are launch engines in existence which do not consume one-half that amount of fuel, but these are so few, so rare, and so expensive, that I have neglected them in this account.
Our present accumulator supplies 33,000 foot-pounds of work per pound of lead, but theoretically one pound of lead manifests an energy equal to 360,000 foot-pounds in the separation from its oxide; and in the case of iron, Prof. Osborne Reynolds told us in this place, the energy evolved by its oxidation is equivalent to 1,900,000 foot-pounds per pound of metal.
Theoretically then, with our weight of fully oxidised lead, we should be able to travel for 82 hours; with the same weight of iron for 430 hours, or 18 days and nights continually, at the rate of 8 miles per hour, with one charge. Of course, these feats are quite impossible. We might as well dream of getting 5 horse-power out of a steam-engine for one pound of coal per hour.
With dynamo machines the aim has been to obtain as nearly as possible as much electrical energy out of the machine as has been put in by the prime mover, irrespective of the quantity of material employed in its construction. Dr. J. Hopkinson has not only improved upon the Edison dynamo, and obtained 94 per cent. of the powers applied in the form of electrical energy, but he got 50 horse-power out of the same quantity of iron and copper where Edison could only get 20 horse-power - and, though the efficiency of this generator is perfect, it could not be called an efficient motor, suitable for locomotion by land or water, because it is still too heavy. An efficient motor for locomotion purposes must not only give out in mechanical work as nearly as possible as much as the electrical energy put in, but it must be of small weight, because it has to propel itself along with the vehicle, and every pound weight of the motor represents so many foot-pounds of energy used in its own propulsion; thus, if a motor weighed 660 pounds, and were travelling at the rate of 50 feet per minute, against gravitation, it would expend 33,000 foot-pounds per minute in moving itself, and although this machine may give 2 horsepower, with an efficiency of 90 per cent., it would, in the case of a boat or a tram-car, be termed a wasteful machine. Here we have an all important factor which can be neglected, to a certain extent, in the dynamo as a generator, although from an economical point of view, excessive weight in the dynamo must also be carefully avoided.
The proper test for an electro-motor, therefore, is not merely its efficiency, or the quotient of the mechanical power given out, divided by the electrical energy put in, but also the number of feet it could raise its own weight in a given space of time, with a given current, or, in other words, the number of foot-pounds of work each pound weight of the motor would give out.
The Siemens D2 machine, as used in the launch shown, is one of the lightest and best motors, it gives 7 horse-power on the shaft, with an expenditure of 9 electrical horse-power, and it weighs 658 lbs.; its efficiency, therefore, is 7-9ths, or nearly 78 per cent.; but its "co-efficient" as an engine of locomotion is 351 - that is to say, each pound weight of the motor will yield 351 footpounds on the shaft. We could get even more than 7 horse-power out of this machine, by either running it at an excessive speed, or by using excessive currents; in both cases, however, we should shorten the life of the apparatus.
With a given energy expressed in watts, we can arrange a quantity of wire and iron to produce a certain quantity of work; the smaller the quantity of material employed, and the larger the return for the energy put in, the greater is the total efficiency of the machine.
Powerful electro-magnets, judiciously arranged, must make powerful motors. The ease with which powerful electro-magnets can be constructed, has led many to believe that the power of an electro-motor can be increased almost infinitely, without a corresponding increase of energy spent. The strongest magnet can be produced with an exceedingly small current, if we only wind sufficient wire upon an iron core. An electro-magnet excited by a tiny battery of 10 volts, and, say, one ampere of current, may be able to hold a tremendous weight in suspension, although the energy consumed amounts to only 10 watts, or less than 1-75th of a horse-power; but the suspended weight produces no mechanical work. Mechanical work would only be done if we discontinued the flow of the current, in which case the said weight would drop; if the distance is sufficiently small, the magnet could, by the application of the current from the battery, raise the weight again, and if that operation is repeated many times in a minute, then we could determine the mechanical work performed. Assuming that the weight raised is 1,000 lbs., and that we could make ana break the current two hundred times a minute, then the work done by the falling mass could, under no circumstances, equal 1-75th of a horse-power, or 440 foot-pounds; that is, 1,000 lbs. lifted 2.27 feet high in a minute, or about one-eighth of an inch for each operation; hence the mere statical pull, or power of the magnet, does in no way tend to increase the energy furnished by the battery or generator, for the instant we wish to do work we must have motion - work being the product of mass and distance.
Large field-magnets are advantageous, and the tendency in the manufacture of dynamo machines has been to increase the mass of iron, because with long and heavy cores and pole pieces there is a steady magnetism ensured, and therefore a steady current, since large masses of iron take a long time to magnetize and demagnetize; thus very slight irregularities in the speed of an armature are not so easily perceived. In the case of electro-motors these conditions are changed. In the first place, we assume that the current put through the coils of the magnets is continuous; and secondly, we can count upon the momentum of the armature, as well as the momentum of the driven object, to assist us over slight irregularities. With electric launches we are bound to employ a battery current, and battery currents are perfectly continuous - there are no sudden changes; it is consequently a question as to how small a mass of iron we may employ in our dynamo as a motor without sacrificing efficiency. The intensity of the magnetic field must be got by saturating the iron, and the energy being fixed, this saturation determines the limit of the weight of iron. Soft wrought iron, divided into the largest possible number of pieces, will serve our purpose best. The question of strength of materials plays also an important part. We cannot reduce the quantity and division to such a point that the rigidity and equilibrium of the whole structure is in any way endangered.
The armature, for instance, must not give way to the centrifugal forces imposed upon it, nor should the field magnets be so flexible as to yield to the statical pull of the magnetic poles. The compass of this paper does not permit of a detailed discussion of the essential points to be observed in the construction of electro-motors; a reference to the main points, may, however, be useful. The designer has, first of all, to determine the most effective positions of the purely electrical and magnetic parts; secondly, compactness and simplicity in details; thirdly, easy access to such parts as are subject to wear and adjustment; and, fourthly, the cost of materials and labour. The internal resistance of the motor should be proportioned to the resistances of the generator, and the conductors leading from the generator to the receiver.
The insulation resistances must be as high as possible; the insulation can never be too good. The motor should, be made to run at that speed at which it gives the greatest power with a high efficiency, without heating to a degree which would damage the insulating material.
Before fixing a motor in its final position, it should also be tested for power with a dynamometer, and for this purpose a Prony brake answers very well.
An ammeter inserted in the circuit will show at a glance what current is passing at any particular speed, and volt-meter readings are taken at the terminals of the machine, when the same is standing still as well as when the armature is running, because the E.M.F. indicated when the armature is at rest alone determines the commercial efficiency of the motor, whereas the E.M.F. developed during motion varies with the speed until it nearly reaches the E.M.F. in the leads; at that point the theoretical efficiency will be highest.
Calculations are greatly facilitated, and the value of tests can be ascertained quickly, if the constant of the brake is ascertained; then it will be simply necessary to multiply the number of revolutions and the weight at the end of the lever by such a constant, and the product gives the horse-power, because, with a given Prony brake, the only variable quantities are the weight and the speed. All the observations, electrical and mechanical, are made simultaneously. The electrical horse-power put into the motor is found by the well-known formula C x E / 746; this simple multiplication and division becomes very tedious and even laborious if many tests have to be made in quick succession, and to obviate this trouble, and prevent errors, I have constructed a horse-power diagram, the principle of which is shown in the diagram (fig. 2).
Graphic representations are of the greatest value in all comparative tests. Mr. Gisbert Kapp has recently made known a useful curve, by means of which one can easily compare the power and efficiency at a glance. (Fig. 3.)
The speeds are plotted as abscissae, and the electrical work absorbed in watts divided by 746 as ordinates; then with a series-wound motor we obtain the curve, E, E. The shape of this curve depends on the type of the motor. Variation of speed is obtained by loading the brake with different weights. We begin with an excess of weight which holds the motor fast, and then a maximum current will flow through it without producing any external work. When we remove the brake altogether, the motor will run with a maximum speed, and again produce no external work, but in this case very little current will pass; this maximum speed is, o, m, on the diagram. Between these two extremes external work will be done, and there is a speed at which this is a maximum. To find these speeds we load the brake to different weights, and plot the resulting speeds and horse-powers as abscissae and ordinates producing the curve, B B. Another curve, e = B/E, made with an arbitrary scale, gives the commercial efficiency; the speed for a maximum external horse-power is o, a, and the speed for the highest efficiency is represented by o, b. In practice it is not necessary to test a motor to the whole limits of this diagram, it will be sufficient to commence with a speed at which the efficiency becomes appreciable, and to leave off with that speed which renders the desired power.
I have now to draw your attention to a new motor of my own invention, of the weight of 124 lbs., which, at 1,550 revolutions, gives 31 amperes and 61.5 volts at terminals. The mechanical horse-power is 1.37, and the coefficient 373.
Armature resistance....... .4w.
Field-magnet resistance.. .17w.
Insulation resistance 1,500,000w.
This motor was only completed on the morning before reading the paper; it could not, therefore, be tested as to its various capacities.
We have next to consider the principle of applying the motive power to the propulsion of a launch. The propellers hitherto practically applied in steam navigation are the paddle-wheel and the screw. The experience of modern steam navigation points to the exclusive use and advantage of the screw propeller where great speed of shaft is obtainable, and the electric engine is preeminently a high-speed engine, consequently the screw appears to be most suitable to the requirements of electric boats. By simply fixing the propeller to the prolonged motor shaft, we complete the whole system, which, when correctly made, will do its duty in perfect order, with an efficiency approaching theory to a high degree.
Whatever force may be imparted to the water by a propeller, such force can be resolved into two elements, one of which is parallel, and the other in a plane at right angles to the keel. The parallel force alone has the propelling effect; the screw, therefore, should always be so constructed that its surfaces shall be chiefly employed in driving the water in a direction parallel to the keel from stem to stern.
It is evident that a finely pitched screw, running at a high velocity, will supply these conditions best. With the beautiful screw made by Messrs. Yarrow, 95 per cent, of efficiency have been obtained when running at a speed of over 800 revolutions per minute, that is to say, only 5 per cent, was lost in slip.
Reviewing the various points of advantage, it appears that electricity will, in times to come, be largely used for propelling launches, and, perhaps, something more than launches.
The Chairman, Mr. W. H. Preece, F.R.S., in inviting discussion, said that no doubt those present would like to know something about the cost of such a boat as Mr. Reckenzaun described, and he hoped that gentleman would give them some information on that point.
Admiral Selwyn suggested that electrical propulsion would be specially applicable to lifeboats. A lifeboat must be expected at times to capsize, and very often to be full of water, which rendered a steam-boiler an impossibility, but perhaps something might be done with electricity. Chemists would agree with him that iron and several other metals could be used for this purpose, some of which combined lightness with the capacity for complete oxidation, and some of which would probably be used in future. But with all that possibility he thought Mr. Reckenzaun was a little below the mark when he talked about the dream of getting 5 horse-power for one pound, he would not say of coal, but of fuel. For some months he had seen one-sixth lb. of fuel produce 1 horse-power, and he knew it could be done. That fuel was condensed concentrated fuel in the shape of oil. In a railway train weight was a formidable affair, but in a floating vessel it was still more important. He did not think, however, that a light secondary battery was by any means an impossibility. Mr. Loftus Perkins had actually produced, by improvements in the boiler and steam-engine, two great things; first, one indicated horsepower for a pound of fuel per hour, and next he had devised a steam-engine of 100 horse-power, of a weight of only 84 lbs. per horse-power, instead of 304 lbs., which was about the average.
Lord Sudeley thought that in the future there would be a very great opening for such boats, depending, no doubt, in great measure on what could be done with secondary batteries, in which there was, as yet, great room for improvement. Then, again, there was the question how far they could be used, unless there were conveniences at different places for charging, or re-charging them. Another important question was, how far these boats could be used in harbour defences, or in torpedo warfare, which would be a great boon, on account of the large amount of space at disposal.
Mr. Crohne (Messrs. Yarrow) said he had the highest opinion of this launch, having carried through the experiments. It was very convenient and pleasant; there was no noise, dirt, or vibration, and in every respect he considered it with great respect.
One very important point in connection with this boat was, that the weight was so low down as to ballast her in the most perfect manner, such as could not be attained in any steamer. The accommodation was very great, and the stability enormous. In the case of a life-boat, the weight being so low down would be of the greatest service; in fact, it would be almost impossible to capsize the boat. He was afraid there was no chance of using such boats for torpedo warfare, torpedo boats being cram-full of steam-power; one of that size, for instance, would be about 100 indicated horse-power; and he did not know how 70 actual horsepower was to be got from electricity in the weight such a boat would carry.
Lieut.-Colonel Webber thought the allusion made by Lord Sudeley to the use of this sort of launch for torpedo purposes was not intended to refer to the so-called torpedo boats mentioned by Mr. Crohne, having a very high speed, but rather to the advantage of having a boat with the large space, such at was here afforded, for the purpose of laying out torpedoes for the defence of harbours. Besides the advantage of a large space, it would allow of a smaller boat being used, which was of great importance, as all would recognise who had been engaged in this service. Again, when torpedoes had to be laid out at night in the neighbourhood of an enemy, the silence, and the absence of glare and reflection from the funnel, would be of the highest advantage.
Mr. Crampton said he did not think steam could ever compete with electricity, under certain circumstances; but, at the same time, it would be a long time before it was superseded. He should like very much to see the compressed oil, one-sixth of a pound of which would give 1 horse-power per hour.
Admiral Selwyn said he had seen a common Cornish boiler doing it years ago.
Mr. Crampton said it had never come under his notice, and he had no hesitation in saying that no such duty ever was performed by any oil, because he never heard of any oil which evaporated more than 18 to 22 lbs. of water per lb.
The Chairman asked if he rightly understood Admiral Selwyn that he had recently seen an invention in which one-sixth of a pound of condensed fuel would give 1 horse-power per hour.
Admiral Selwyn said it was now some years ago since he saw this thing going on, but the persons who did it did not know how or why it was done. He had studied the question for the last ten years, and now knew the rationale of it, and would be prepared shortly to publish it. He knew that 22 was the theoretical calorific value of the pound of oil, and never supposed that oil alone would give 46 lbs., which he saw it doing. He had found out that by means of the oil forming carbon constantly in the furnace, the hydrogen of the steam was burned, and that it was a fallacy to suppose that an equal quantity of heat was used in raising steam, at a pressure of, say, 120 lbs. to the square inch, as the hydrogen was capable of developing when properly burned. There were, however, conditions under which alone that combustion could take place - one being that the heat of the chamber must be 3,700°, and that carbon must be constantly formed.
Mr. Gumpel said it was not so much the present position of the electric launch, as its promise for the future, which was of interest and importance. One point to which he would call attention was the great speed of the propeller. It had about 9 inches pitch, and worked at 800 revolutions a minute. He believed that if Mr. Reckenzaun could construct a motor which would give a less number of revolutions, but develop the same amount of propelling power, there would be greater efficiency. With regard to the general application of electricity to the propulsion of vessels as well as to railway trains, he believed that many of those present would live to see electricity applied to that purpose, because there were so many minds now applied to the problem, that before long he had no doubt we should see coal burned in batteries, as it was now burned in steam boilers. The utmost they could do, then, would be about 50 per cent. less than Admiral Selwyn said could be accomplished with condensed fuel. He could not but wonder where Admiral Selwyn obtained his information, knowing that a theoretically perfect heat-engine would only give 23 per cent. of the absolute heat used, and that a pound of the best coal would give but 8,000 and hydrocarbon 13,000 heat units, whilst hydrogen would give 34,000, and calculating it out, how was it possible to get out of one-sixth of a pound of carbon, or any hydrocarbon, the amount of power stated. No doubt, when Admiral Selwyn applied the knowledge which physicists would give him of the amount of power which could be got out of a certain amount of carbon and hydrogen, he would find that there was a mistake made somewhere. He greatly admired the manner in which Mr. Reckenzaun had brought forward the subject, which formed a pleasant contrast to some papers they had heard from inventors of particular motors; and he thought it would be very useful if he would prepare another paper on the different forms of motors, and the conditions necessary for their efficiency.
Mr. Reckenzaun, in reply, said it would be very difficult to answer the question put by the chairman, as to the cost of an electric launch - quite as difficult as to say what would be the cost of a steam launch. It depended on the fittings, the ornamental part, the power required, and the time it was required to run. If such a launch were to run constantly, two sets of accumulators would be required, one to replace the other when discharged. This could be easily done, the floor being made to take up, and the cells could be changed in a few minutes with proper appliances. As to Admiral Selwyn's remarks about one-sixth of a pound of fuel per horse-power, he had never heard of such a thing before, and should like to know more about it. Mr. Loftus Perkin's new steam-engine was a wonderful example of modern engineering. A comparatively small engine, occupying no more space than that of a steam launch of considerable dimensions, developed 800 horse-power indicated. From a mechanical point of view, this engine was extremely interesting; it had four cylinders, but only one crank and one connecting rod; and there were no dead centres. The mechanism was very beautiful, but would require elaborate diagrams to explain. Mr. Perkins deserved the greatest praise for it, for in it he had reduced both the weight of the engine and the consumption of fuel to a minimum. He believed he used coke, and took one pound per horse-power. He should not like to cross the Channel in the electric launch, if there was a heavy sea on, for shaking certainly did not increase the efficiency of the accumulators, but a fair amount of motion they could stand, and they had run on the Thames, by the side of heavy tug-boats causing a considerable amount of swell, without any mishap. Of course each box was provided with a lid, and the plates were so closely packed that a fair amount of shaking would not affect them; the only danger was the spilling of the acid. Mr. Crohne had remarked that a torpedo boat of that size would have 100 indicated horse-power, but then the whole boat would be filled with machinery. What might be done with electricity, they had, as yet, no idea of. At present, they could only get 33,000 foot pounds from 1 lb. of lead and acid, though, theoretically, they ought to get 360,000 footpounds. Iron, in its oxidation, would manifest theoretically 1,900,000 foot-pounds per lb. of material. As yet they had not succeeded in making an iron accumulator; if they could, they would get about six or seven times the energy for the same weight of material, or could reduce the weight proportionately for the same power, and in that way they might eventually get 70 horse-power in a boat of that size, because the weight of the motor was not great. With regard to the formation of a film on the surface, no doubt a film of sulphate of lead was formed if the battery stood idle, but it did not considerably reduce its efficiency; as soon as it was broken through by the energy being evolved from it, it would give off its maximum current. They knew by experience that, with properly constructed accumulators, 80 per cent. of the energy put into them was returned in work. With regard to Mr. Gumpel's remark on the propeller, he would say that it was constructed to run 900 revolutions; if it were driven by a steam-engine, and the speed reduced to 300, not only would the pitch have to be altered, but the surface would have to be larger, which would entail more friction. Mr. Crohne would bear him out that they lost only 5 per cent, by slip and friction combined, on an average of a great number of trials, both with and against the current.
Mr. Gumpel remarked that Sir E. J. Reed had pointed out in that room that it was a fallacy to suppose that slip in itself was a loss. You must have slip for the purpose of propelling the vessel. The 5 per cent. loss would not give any idea of the efficiency of the propellor in itself.
Mr. Crohne said he had always been of opinion that such a fine pitch would not do at all, and they had an electric launch made with gear to reduce the speed of the propeller; but, practically, he found he was mistaken. He had expected that negative slip and the friction of the propeller would be a serious impediment, but he found he was entirely mistaken. This wonderfully fine pitch of about 10 inches, and a diameter of 20 inches, was quite unknown before, as far as he was aware, but it gave very good results indeed.
The Chairman, in proposing a vote of thanks to Mr. Reckenzaun, said he rejoiced to find that that gentleman had proved, to one practical man at least, that his views had been mistaken. He found in these days of the practical applications of electricity, that the ideas of most practical men were gradually being proved to be mistaken, and every day new facts were being discovered, which led them to imagine that as yet they were only on the shore of an enormous ocean of knowledge. It was quite impossible to Bay what these electric launches would lead to. Enormous strides were being made with regard to secondary batteries. No one present had been a greater sceptic with regard to them at first than he himself; but after constant experiments - employing them, as he had done for many months, for telegraphic purposes - he was gradually coming to view them with a much more favourable eye. He must congratulate Mr. Reckenzaun on the excellent diagrams he had constructed. The trouble of calculating figures of this sort was very great when making experiments; and the use of diagrams and curves expedited the labour very much. At present they were passing through a stage of electrical depression; robbery had been committed on a large scale; the earnings of the poor had been filched out of their pockets by sanguine company promoters; an enormous amount of money had been lost, and the result had been that confidence was, to a great extent, destroyed. But those who had been wise enough to keep their money in their pockets, and to read the papers read in that room, must have seen that there was a constant steady advance in scientific knowledge of the laws of electricity and in their practical applications, and as soon as some of these rotten mushroom companies had been wiped out of existence, they might hope that real practical progress would be made, and that the day was not far distant when the public would again acquire confidence in electrical enterprise. They would then enable inventors and practical men to carry out their experiments, and to put electrical matters on a proper footing.