Chapter 5

In deciding upon the relative merits of the several motors, so far as the eight points included under this heading are concerned, it is clear that, except possibly as regards absence of noise, the electrical car surpassed all the others.

The compressed air car followed, in its superiority in respect of the first three points, viz., absence of steam, absence of smoke, and absence of noise; but the Rowan was considered superior in respect of the other points included in this class.

Under the letter B have been classed considerations of maintenance and construction.

9. Protection, more or less complete, of the machinery against the action of dust and mud. 10. Regularity and smoothness of motion. 11. Capacity for passing over curves of small radius. 12. The simplest and most rational construction. 13. Facility for inspecting and cleaning the interior of the boilers. 14. Dead weight of the train compared with the number of places. 15. Effective power of traction when the carriages are completely full. 16. Rapidity with which the motor can be taken out of the shed and made ready for running. 17. The longest daily service without stops other than those compatible with the requirements of the service. 18. Cost of maintenance per kilometer. (It was assumed, for the purposes of this sub-heading, that the motor or carriage which gave the best results under the conditions relating to paragraphs 9, 10, 12, and 13 would be least costly for repairs.)

As regards the first of these, viz., protection of the machinery against dirt, the machinery of the electrical car had no protection. It was not found in the experiments at Antwerp that inconvenience resulted from this; but it is a question whether in very dusty localities, and especially in a locality where there is metallic dust, the absence of protection might not entail serious difficulties, and even cause the destruction of parts of the machinery.

In respect to the smoothness of motion and facility of passing curves, the cars did not present vary material differences, except that the cars in which the motor formed part of the car had the preference.

In the case of simplicity of construction, it is evident that the simplest and most rational construction is that of a car which depends on itself for its movement, which can move in either direction with equal facility, which can be applied to any existing tramway without expense for altering the road, and the use of which will not throw out of employment vehicles already used on the lines; the electric car fulfilled this condition best, as also the condition numbered 13, as it possessed no boiler.

In respect to No. 14, viz., the ratio of the dead weight of the train to passengers, if we assume 154 lb. as the average weight per passenger, the following is the result in respect of the three cars in which the power formed part of the car:

9,350 lb. Electric car. --------- = 1.78 154 × 34

15,950 lb. Rowan. ---------- = 2.30 154 × 45

22,000 lb. Compressed air. ---------- = 2.55 154 × 56

The detached engines gave, of course, less favorable results under this head.

Under head No. 15 the tractive power of all the motors was sufficient during the trials, but the line was practically level, therefore this question could only be resolved theoretically, so far as these trials were concerned, and the table before given affords all the necessary data for the theoretical calculation.

As regards the rapidity with which the motors could be brought into use from standing empty in the shed, the electric car could receive its accumulators more rapidly than could the boiler for heating the exhaust of the compressed-air car be brought into use.

As regards the steam motors, the following were the results from the time of lighting the fires:

The Rowan-- In 34 minutes 3 atmospheres. " 36 " 4 "

At this pressure the vehicle could move--

In 40 minutes 8 atmospheres.

The Wilkinson-- In 35 minutes 2 atmospheres. " 40 " 4 " " 44 " 6 " " 47 " 8 "

The Krauss machine required two hours to give 6 atmospheres, which was the lowest pressure at which it could be worked.

The results under No. 17, viz., the fewest interruptions to the daily service, class the motors in the following order: Krauss, electric, Rowan, Wilkinson, compressed air. The chief cause of injury to the compressed air motor arose from the carelessness of the drivers, who allowed the steam boiler to be burnt out. Unfortunately, these drivers were new to the work.

Under the letter C are classed considerations of economy in the consumption of materials used for generating the power necessary for working.

19. Minimum consumption of fuel (either coke or coal), in proportion to the number of kilometers run, and to the number of places, assuming for the seats a width of at least sixteen inches for each person seated.

It must be borne in mind that the conditions of the competition required that a second car should be periodically drawn by the motor, and that the calculations which follow include the total number of miles run, the total amount of fuel, etc., consumed, and the total number of passengers which could be conveyed by each motor, during the total time that the experiments were being carried on.

TABLE II.

Total Description of motor. number of Total No. of lb. train miles Consumption per run. of fuel. train mile.

lb. Electric. 2,358.9 14 786 6.16 Rowan. 2,616.9 14,498 5.42 Wilkinson. 2,473.3 22,000 8.82 Krauss. 2,457.8 22,726 9.10 Compressed air. 2,259.1 90,420 39.48

TABLE III.

No. of places No. of lb. of Description of motor. indicated on fuel consumed the cars, per Consumption per places mile run. of fuel. indicated per mile run. lb. Electric 80,203.5 14,786 0.18 Rowan 148,399.6 14,498 0.09 Wilkinson 119,085.1 22,000 0.18 Krauss 108,983.9 22,726 0.20 Compressed air 128,189.3 90,420 0.69

TABLE IV.

Description of motor. No. of seats per No, of lb. of mile run. Consumption fuel consumed of fuel. per seat per mile run. lb. Electric 61,591.2 14,786 0.23 Rowan 135,928.8 14,498 0.10 Wilkinson 93,965.6 22,000 0.23 Krauss 86,039.9 22,726 0.25 Compressed air 132,732.7 90,420 0.66

As regards the figures in these tables, it is to be observed that the consumption of fuel for the electric car is, to a certain extent, an estimate; because the engine which furnished the electricity to the motor also supplied electricity for electric lights, as well as for an experimental electric motor which was running on the lines of tramway, but was not brought into competition.

20. Minimum consumption of oil, of grease, tallow, etc. (the same conditions as in No. 19).

TABLE V.

Total Consumption Total consumption of oil, tallow, Description of number of of etc., motor. miles run. oil, tallow, per train mile etc. run.

lb. Electric 2,358.9 99.0 0.038 Rowan, steam 2,616.9 106.7 0.038 Krauss, steam 2,457.8 188.5 0.073 Wilkinson, steam 2,473.3 255.4 0.101 Compressed air 2,259.1 585.2 0.255

In addition to these considerations, it was thought useful to investigate the quantity of water consumed in the case of those engines which used steam. The experiments made on this point showed as the consumption of water:

Gallons per mile. Rowan 0.75 Compressed air 1.06 Wilkinson 5.89 Krauss 6.52

Thus, owing to the large proportion of water returned from the condenser to the tanks, the Rowan actually used less water than the compressed air engine.

CONCLUSION.

The general conclusion to which these experiments bring us is that, undoubtedly, if it could certainly be relied upon, the electric car would be the preferable form of tramway motor in towns, because it is simply a self-contained ordinary tram-car, and in a town the service requires a number of separate cars, occupying as small a space each as is compatible with accommodating the passengers, and which follow each other at rapid intervals.

But the practicability and the economy of a system of electric tram-cars has yet to be proved; for the experiments at Antwerp, while they show the perfection of the electric car as a means of conveyance, have not yet finally determined all the questions which arise in the consideration of the subject. For instance, with regard to economy, the engine employed to generate the electricity was not in thoroughly good order, and from its being used to do other work than charging the accumulators of the tram-car, the consumption of fuel had to be to some extent estimated. In the next place, the durability of the accumulators is still to be ascertained; upon this much of the economy would depend. And in addition to this question, there is also that of the durability of parts of the machinery if exposed to dust and mud.

After the electric car, there is no question but that at the Antwerp Exhibition the most taking of the tramway motors was the Rowan, which was very economical in fuel, quite free from the appearance of steam, and very convenient and manageable.

The economy of the Rowan motor arises in a large degree from the extent of its condensing power, by means of which a considerable supply of warm water is constantly supplied for use in the boiler, and consequently the quantity of water which has to be carried is lessened, and the fuel is economized.

Independently, however, of its convenience as a motor for tramways in towns, the Rowan machine has been adapted on the Continent to the conveyance of goods as well as passenger traffic on light branch railways, and fitted to pass over curves of 50 feet radius, and up gradients of 1:10.

In England, with our depressed trade and agriculture, there is a great want in many parts of the country of a cheap means of conveyance from the railway stations into the surrounding districts; such a means of conveyance might be afforded by light railways along or near the road-side, the cost of which would be comparatively small, provided that the expensive methods of construction, of signaling, and of working which have been required for main lines, and which are perfectly unnecessary for such light railways, were dispensed with.

It is certain that this question will acquire prominence as soon as a system of local government has been adopted, in which the wants of the several communities have full opportunity of asserting themselves, and in which each local authority shall have power to decide on those measures which are essential to the development of the resources of its own district, without interference from a centralized bureaucracy.

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ON THE THEORY OF THE ELECTRO-MAGNETIC TELEPHONE TRANSMITTER.

By E. MERCADIER.

[Footnote: Note presented to the Academy of Sciences, Oct. 19, 1885.]

The first point to be studied in this theory is the _role_ performed by the iron or steel diaphragm of the telephone, both as regards the nature of the movements that it effects through elasticity and the conversion of mechanical into magnetic energy as a result of its motions.

I. When we produce simple or complex vibratory motions in the air in front of the diaphragm, like those that result from articulate speech, either the fundamental and harmonic sounds of the diaphragm are not produced, or else they play but a secondary _role_.

(1.) In fact, diaphragms are never set in vibration, as is supposed, when we desire to determine the series of harmonics and nodal lines, since we do not leave them to themselves until they have been set in motion, and we do not allow a free play to the action of elastic forces; in a word, the vibrations that they are capable of effecting are constantly _forced_ ones.

(2.) When a disk is set into a groove, and its edges are fixed, theory indicates that the first harmonics of the free disk should only rise a little. Let us take steel disks 4 inches in diameter and but 0.08 inch in thickness, and of which the fundamental sound in a free state is about _ut_{5}_, and which the setting only further increases. It is impossible to see how this fundamental and the harmonics can be set in play when a continuous series of sounds or accords below _ut_{5}_, are produced before the disk; and yet these sounds are produced perfectly (with feeble intensity, it is true, in an ordinary telephone) with their pitch and quality. They produce, then, in the transmitting diaphragm other motions than those of the fundamental sound and of its peculiar harmonics.

(3.) It is true that in practice the edges of the telephone diaphragm are in nowise fixed, but merely set into a groove, or rather clamped between wooden or metallic rings, whose mass is comparable to their own; and they are, therefore, as regards elasticity, in an ill ascertained state. Yet a diaphragm of the usual diameter (from 2 to 4 inches), and very thin (from 0.001 to 0.02 inch), clamped in this way by its edges, is capable of vibrating when a continuous series of sounds are produced near it, by means, for example, of a series of organ pipes. But the series of sounds that it clearly re-enforces, in exhibiting a kind of complex nodal lines, is plainly _discontinuous_; and how, therefore, would the existence of such series suffice to explain the production of a _continuous_ scale of isolated or superposed sounds, the chief property of the telephone?

(4.) The interposition of a plate of any substance whatever between the diaphragm and the source of the vibratory motions in nowise alters the telephonic qualities of the diaphragm, and consequently the _nature_ of the motions that it effects--a fact that would be very astonishing if the motions were those that corresponded to the peculiar sounds of the diaphragm. This fact is already known, and I have verified it with mica, glass, zinc, copper, cork, wood, paper, cotton, a feather, soft wax, sand, and water, even in taking thicknesses of from 5 to 8 inches of these substances.

(5.) We can put a diaphragm manifestly out of condition to effect its peculiar scale of harmonics by placing small, unequal, and irregularly distributed bodies upon its surface, by cutting it out in the form of a wheel, and by punching a sufficient number of holes in it to reduce it half in bulk. None of these modifications removes its telephonic qualities.

(6.) We can go still further, and employ diaphragms of scarcely any stiffness and elasticity without altering their essential telephonic properties, the reproduction of a continuous series of sounds, accords, and timbres. Such is the case with a sheet iron diaphragm. It is very difficult, then, to imagine a fundamental sound and its harmonics.

The conclusion from all this appears to me to be that the mechanism by virtue of which telephone diaphragms perform their motions is at least analogous to, if not identical with, that through which solid bodies of any form whatever (a wall, for example) transmit to all of their surfaces all the simple or complex successive or simultaneous vibratory motions, of periods varying in a continuous or discontinuous manner, that are produced in the air in contact with the other surface. In a word, we have here a phenomenon of _resonance_. In diaphragms of sufficient thickness this kind of motion would exist alone. In thin diaphragms the motions that correspond to their special sounds might become superposed upon the preceding, and this would be prejudicial rather than useful, since, in such a case, if there resulted a re-enforcement of the effects produced, it would be at the expense of the reproduction of the timbre, the harmonics of the diaphragm being capable of coinciding only through the merest accident with those of the sounds that were setting in play the fundamental sound of the diaphragm. This is what experiment clearly demonstrates.

II. Let us now pass to the _magnetic role_ of the telephone diaphragm. Such _role_ can be clearly enough defined by the following facts:

(1.) The presence of the magnetic field of the telephone in nowise changes the preceding conclusions.

(2.) Upon farther and farther diminishing the stiffness and elasticity of the diaphragm, I have succeeded in suppressing it entirely. In fact, it is only necessary to substitute for it, in any telephone whatever, a few grains of iron filings, thrown upon the pole of the magnet, covered with a bit of paper or cardboard, in order to render it possible to reproduce all sounds, and articulate speech with its characteristic quality, although, it is true, with very feeble intensity.

(3.) In order to increase the intensity of the effect produced, it suffices to substitute for the iron diaphragm a thin disk of any sort of slightly flexible substance, metallic or otherwise, cardboard, for example, and through the aperture of the usual cover of the instrument to scatter over it from 1½ to 3 grains of iron filings. In this way we obtain an iron filings telephone. By properly increasing the intensity of the magnetic field, I have been able to form telephones of this kind that produced in an ordinary receiver as intense effects as those given by the usual transmitters with stiff disks, and which, too, were reversible. But for a field of given intensity, there is a weight of iron filings that produces a maximum of effect.

We thus see that the advantage of the iron diaphragm over filings is truly reduced to the presentation of a much larger number of magnetic molecules to the action of the field and to external actions, within the same volume. It increases the _intensity_ of the telephonic effects, although for _the production_ of the latter with all their variety, fineness, and perfection it is nowise indispensable. It suffices, after a manner, to materialize the lines of force with iron filings, and to act mechanically upon them, and consequently upon the field itself.

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ON THE THEORY OF THE RECEIVER OF THE ELECTRO-MAGNETIC TELEPHONE.

By E. MERCADIER.

[Footnote: Note presented to the Academy of Sciences, November 16, 1885.]

On a former occasion I described some experiments that had led me to a theory of the telephone transmitter; a few words will suffice to expose that of the receiver.

Such theory gave rise during the first years succeeding the invention of the telephone to a considerable number of investigations, the principal results of which may be summed up in the two following points:

1. All the parts of a telephone receiver--core, helix, disk, handle, etc.--vibrate simultaneously (Boudet, Laborde, Breguet, Ader, Du Moncel, and others). But there is no doubt that by far the most energetic effects are those of the disk. It has been possible to put the vibrations of the core and helix beyond a doubt only by employing very energetic transmitter currents, or very simplified and special arrangements of the receiver (Ader, Du Moncel, and others).

2. In telephone receivers we may employ disks or diaphragms of any thickness up to six inches (Bell, Breguet, and others).

From the first point it had already resulted that the diaphragm was no more indispensable in the receiver than it was in the transmitter, as I have already shown (_Comptes Rendus_, t. ci., p. 944); and, from the second point, that there were other effects in a receiver than those that could result from the transverse vibrations corresponding to the fundamental sound and to the harmonics of the diaphragm.

So Du Moncel, basing a theory upon these two categories of facts, asserted that the effects of the telephone receiver were principally due to the molecular vibrations of the core of the electro-magnet (analogous to those that had been studied by Page, De la Rive, Wetheim, Reis, and others), super-excited and re-enforced by the iron diaphragm operating as an armature.

This theory has certainly truth for a basis; but it is incomplete, in that the molecular vibrations of the core are but a very feeble accessory phenomenon, and not a prominent one. At all events, I believe that we can, in a few words, and very simply, present the theory of the telephone receiver by going back to the facts that served me as a basis for the theory of the transmitter, and that result from studies made with telephones of ordinary forms.

In fact, it is enough to remark that the iron filings telephone transmitter described in a preceding article (_1. c_.) is reversible and capable of serving as a receiver--not a very intense one, it is true, but here it is a question of the _nature_ of the phenomena, and not of their intensity. It at once results that in receivers, as in transmitters, the rigidity of the iron diaphragm is in nowise indispensable for telephonic effects, such as the production of continuous series of successive or simultaneous sounds and of articulate speech.

The diaphragm serves but to increase the intensity of these effects, as in the transmitter, by concentrating the lines of force of the field, and by presenting a greater surface to the air--the necessary vehicle of sound. When it is thick, the internal motions that it takes on in consequence of variations in the field, and which are transmitted to the surrounding air and the ear, are solely those of resonance. When it is very thin, the peculiar motions resulting from its geometric form and its structure may become superposed upon the preceding, because it may then happen that the corresponding sounds remain within the limits of the pitch wherein the human voice usually moves (from ut_{2} to ut_{5}); but then, also, as the harmonics of the voice in nowise coincide with the proper sounds of the diaphragm, the intensity of the effects is obtained at the expense of a good reproduction of the timbre. This is certainly one of the causes of the nasal timbre of most thin-diaphragmed telephones. By diminishing their thickness, we lose in quality what we gain in intensity.

But even in this latter respect there is a maximum for receivers, as I have already pointed out that there is for iron filings transmitters. For a magnetic field of given intensity, there is, all things equal, a diaphragm thickness that gives a maximum telephonic result. Such result, which is analogous to those that occur in other electro-magnetic phenomena, may explain the want of success of many tentatives made somewhat at haphazard, with a view to increasing the intensity of telephonic effects.

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DECOMPOSITION AND FERMENTATION OF MILK.