tion of this law. The proposition that the weight of the conductor must increase as the square of the distance, is now regarded by Dr. Siemens as one which, though true in itself, will lead to very erroneous conclusions as to the practicability of transmitting power unless further considerations are added. It has been found that the economical limit to the resistance in an electric machine or conductor is about one of the electric units, known by the name of ohm; as, if that degree of resistance is exceeded, a loss of current ensues through the heating of the coil. Mr. Sabine states the conducting resistance of an average wire of No. 4 Birmingham wire gauge (which is equal to a diameter of 0.238 inches) at 7·7 ohms per statute mile. sistance on the electric telegraph current from London to Birmingham is stated by Mr. Preece as 1500 ohms (written 1500). The dynamic equivalent of the ohm is not mentioned by Mr. Sabine in the work referred to, or by Mr. Preece in a larger volume. The volt, which is the unit of electromotive force, as the ohm is of resistance, absorbs 44:24 foot-pounds per second. 1 H.P. is equal to 766 volt-ohms, and is equivalent to the consumption of grammes of zinc per second in a Daniell's cell, or 895-2 grammes per hour. If, therefore, argues Dr. Siemens,

746

3000

The re

there is a machine with one ohm resistance, there ought to be a conductor transmitting the power with a resistance of not more than one ohm. If, instead of conveying the energy for one mile, it is desired to carry it for two miles, the length of the conductor will be doubled. But by this change the resistance will also be doubled, or become equal to two ohms, and much of the useful effort of the original force will thus be lost. To reduce the resistance to one ohm it would

be necessary to lay down a second wire or to double the cross-section of the first wire. In that case there would, of course, be a wire of twice the length and twice the area that is to say, of four times the weight of the first. That points, as before said, to an increase in the weight, and approximately in the cost, of the conductor in the ratio of the square of the distance.

But here comes in the observation that the electric conductor does not resist the motion of electricity in the same way as that in which a pipe resists the flow of water through it. An ohm's resistance is an ohm's resistance, whether the current flowing through the conductor is larger or smaller. The only limit to sending ing which they cause in the conmore powerful currents is the heatductor. According to Mr. Sabine, this resistance increases 0.2 per cent. for each Fahrenheit degree of temperature in the conductor. As the fourfold conductor would have four times the superficies of the original conductor, the dissipation

of heat would be also four times the amount of that occurring in the first instance; and thus, says Dr. Siemens, the doubled conductor would be capable of transmitting four times the amount of electric current.

Dr. Siemens adds that, if one wire of double area be substituted for two wires, the superficies will not be doubled, but will only be increased in the ratio of 2√1⁄2 to 1; and the relative transmitting power will not be increased in a higher ratio than that of 1 to 2√2, or 1 to 2.83. If the obstruction arises from the actual temperature of the conductor, it would be reduced by substituting thin laminæ of metal for a solid wire. If it be actual conversion of heat, it is difficult to see how the more or less

free radiation and escape of the heat can reduce the loss of power in the current.

This view of Dr. Siemens, when brought forward by him at the Institution of Civil Engineers, in January, 1878, was at once hailed by Sir William Thomson, the Professor of Natural History at the University, Edinburgh, who was for five years President of the Royal Society of Edinburgh, as "quite new, and of great practical importance." The question of the heat developed in the wire was, Sir William remarked, the fundamental question with reference to the quantity of metal required to communicate the effect to a distance. It appeared to him that the most practical way of producing the result would be to put the wire in the shape of a copper tube. current of water might be made to flow through this tube, and to carry off the heat as it was deveoped.

A

In April last, in giving evidence before the Select Committee on lighting by electricity, Dr. Siemens again stated that the only limit to the transmitting power of a long conductor is its liability to become heated; for, "in transmitting an electrical current through a conductor, a portion of the dynamical effect of the energy is lost and converted into heat, which heat accumulates in the conductor, and has to be disposed of by radiation or conductor." Here direct loss is mentioned; nor is there reference made to any electrical resistance caused by a heated conductor, though physical inconvenience seems to be anticipated. If the resistance of the conductor is made equal to that of the dynamo-electric machine itself, it follows, Dr. Siemens says, from the recent experiments of Dr. Hopkinson, that the loss does not exceed ten per cent. of the power employed.

One-tenth of the total power employed would, therefore, go to heat the conductor; and if that conductor is exposed to the cooling influence of the atmosphere, it would be able to transmit a vast amount of electric energy. Dr. Siemens concluded by stating it as his opinion that a conductor of two inches diameter would probably suffice to convey electric energy equal to 1000 horse-power to a distance of thirty miles. The

general testimony is, in his opinion, that about fifty per cent. of the motive power is lost in transmission.

com

On the 23rd May, in giving evidence before the Select Committee on electric lighting, Sir W. Thomson reiterated the views he had expressed at the Institution of Civil Engineers, entering further into detail. He told the mittee, "I look forward to the falls of Niagara being extensively used for the production of light and mechanical power over a large area of North America." He considered that this power might be "advantageously transmitted for hundreds of miles." He "had no limit to the application of it on a great scale." It could do all the work which is done by steam engines. Sir William furnished a carefully written reply to several questions as to the size of the conductors, in which he gives a formula taking the resistance in ohms from Clark and Sabine's electrical table and formulæ as indicated by the expression ; when L is the length of the conductor in statute miles, and d is its diameter in tenths of an inch. Sir William has come to the conclusion, "assuming 20 per cent. to be lost in transit," that a copper wire of half an inch in diameter would transmit 21,000 horse-power for a distance of 300 statute miles; the power sent in

5.5 X L

d2

being that of 26,250 horses, and that brought out being 80 per cent. of the same. But no explanation

is given as to why 20 per cent. loss is "assumed." Dr. Siemens, as we have seen, gives 50 per cent. as the proportionate efficiency, which might be further reduced by the development of heat. Sir William Thomson's formula can only give useful results when it is shown what are the facts on which the value "lost in transit" is calculated. Sir William calculates (on the assumed 20 per cent. loss) that the generation of heat in the main conductor will be at the rate of about of a French thermal unit per square centimètre of surface per second. The rate of loss of heat by variation and convection he gives as about 000 per square centimètre per degree of excess of temperature above that of the surrounding medium. Then, he argues, the main conductor, if freely exposed to air, will be raised only 20 degrees Centigrade by the heating effect of the current, and the use of tubular conductors will be unnecessary. In this communication Sir William gives the expression, P= the proportion of work lost in transit, in virtue of the resistance of the conductor. But as all that he says as to this is " suppose here 20 per cent. to be lost in transit," we do not obtain anything more from the working out of an equation containing expressions raised to the 24th power, than is involved in that supposition. It is very tantalising to be presented with so evidently imperfect a paper by the printer of the report of the committee.

We have gone with considerable care into the exact language employed by the most eminent men who have recently expressed their views

on this highly-important question of the limitation of the transmissibility of the electric

energy. We have done so with the more anxiety from the fact that contradictory and unintelligible statements have lately appeared on the subject. But whatever be the cause, there is far more obscurity than we could wish in the statements of the eminent men who so recently gave the evidence which we have cited. One reason, no doubt, may be, that the inquiry of the committee was recently directed to lighting by electricity, while our own inquiries have been into the far broader and more comprehensive question of the transmission of power. But it must be remembered, on the other hand, that all the numerous and complicated questions as to regulators, lamps, and generative machines, are laid on one side in our investigation. What we seek to do is to find how far, from accessible sources of information, the idea of the absence of direct functional relation between the quantity of energy transmissible and the resistance to transmission is established. The economical properties of the resistance of circuit and machine is laid down. The effect of length and area of conductor on resistance is prescribed. What we want to understand is, with a given conductor, what will be the increased resistance of an increased current.

As to this, it is disappointing to find that, after announcing their accord, eighteen months ago, Dr. Siemens and Sir William Thomson are now so wide in their reckonings. The one requires for transmitting an energy of 1000-horse power for the distance of thirty miles, a conductor of two inches diameter, with a resulting loss of 50 per cent. of initial energy. The other gives, for transmitting an initial energy of 26,250 horse power for a distance of 300 miles, a conductor of half an inch diameter, and a loss in transit of

20 per cent. There is no harmony, no balance, no relation, between the two estimates. The more eminent is the character of each of the two electricians who have come forward to instruct the committee, and, through them, the scientific world, the more do we regret that the evidence has been allowed to see the light in a form so utterly perplexing to the scientific inquirer.

No

It

That the transmissibility of the electric energy is not so sharply limited as was held to be the case when the rule of increase of cost of conductors in proportion to the square of the distance was first formulated, we believe has been experimentally ascertained. In what precise manner that modification has occurred, if it has been ascertained by any electrician, has not been made known. inquiry can have more importance. It is true that the point of research, however successful, does not promise to enrich the observer. He will gain nothing by it-nothing, at least, but immortal fame. cannot, from its nature, we apprehend, be made the subject of a patent. This is probably the reason of the apparent anomaly, that while great care and skill has been bestowed on every minor detail of electro-telegraphy, electrophonography, and electro-lighting, a grand question which underlies, not only these subjects, but the whole question of the future source of power, should have been allowed to come before the world in so tangled, confused, and contradictory a shape. We cannot, of course, blame scientific men for giving their time to those branches of study which promise a lucrative return. The inducement of interest is in itself a good one, and most of what we have obtained of late years has been due to that powerful motive.

None the less is it matter for

regret that there should not be found among us men whose circumstances would allow them, and whose tastes would lead them, to follow the study of science for its own sake for its own, and for that of the great benefits promised to the world. From the earliest time of which we have any record, in works of a philosophical or a magical character, the research of perpetual motion has been more or less closely connected with that of the "elixir of life," and of the conversion of base metal into gold. In discovering how the heat stored up in coal might be made to do the work of man and of beast, Watt gave us, as it were, an instalment of perpetual motion; he gave us a source of power, external to the animal world, and almost limited, except by time, in its applicability. Still, a certain cost attended the attainment of this new source of power; and, as matter of fact, though it concerns those who shall come after us more than ourselves, this stored-up supply of solar heat is limited in quantity, as well as somewhat costly to procure.

un

A more inexhaustible source of motive power is presented by the great periodic phenomena of nature, especially by the tidal force and by the flow of great rivers. The supply here is absolutely inexhaustible, as well as, in itself, costless. Nor would the apparatus necessary for grasping this power be of a cost at all prohibitory. The only barrier to retard our strides in this direction lies in the difficulty of transmission.

We should fall into the very evils against which we desire to warn our friends if we were to speak in sanguine terms of this difficulty as now overcome. But at least we have warrant, in the serious statements of men of practical science, for the hope that there is

something to be done in that direction; what we anxiously desire is, the free and full investigation of the subject. As far as matters have gone hitherto, it seems that one great source of waste is not now regarded as affecting the transmission of powerful electric currents. No one who has spoken on the subject has seemed to fear loss by leakage, so to speak, of the energy, by conduction or induction, or by want of isolation in the conductors. If this be so, it is a great point gained. What is needed is to have this stated clearly, distinctly, and authoritatively. Then comes the question of resistance. Here the difference of statement, as before shown, is so wild that we are brought sharply to a stand. But for all that we will not give up the hope that facts are better known to experts than they are to the public; that men of science, if they have not the gift of clear speaking, or of clear writing, have that of clear thinking. This matter of the effect of heating on the conductor is one which, it strikes us, it is of primary importance now to have fully thrashed out. Is it loss of power of current, or is it definite increase of resistance with which we have most to contend? Is the effect of heating the conductor to be chiefly deprecated on electric or on physical grounds? These are questions which a committee, however select, is a most inefficient, and therefore really a most costly manner of solving. In the present case the names of many members of the committee, as well as of many of the witnesses, are those of eminent men; but their power was as much wasted by the mode of conducting the inquiry, as is that of a dynamo-electric machine when applied through an imperfect conductor. A country such as England ought to be ashamed to beg for scraps of scientific infor

mation. It ought to be ashamed to filch an hour or two of the time of eminent scientific men gratis. It is a natural consequence of such a proceeding that the witnesses merely repeat what they may have said or written elsewhere, while any power of reconciling apparent contradictions is wholly absent. Half a dozen or more names might be selected, either from the committeemen or from the witnesses, the owners of either of which, if offered 5001. for his trouble, would soon be able to present the world with a report that would at all events have placed on record what was known, and would have brought down our knowledge of the subject to include the latest actual discoveries.

As far as the report of the committee goes, it cannot be accused of precipitation. It begins by saying, "The general nature of the electric light has been well explained in the evidence." It goes on, "It is not surprising that, while many practical witnesses see serious difficulties in the speedy application of the electric light to useful purposes of illumination, the scientific witnesses see in this economy of force the means of great industrial development." That is rather a meagre outcome of a ten days' inquiry! As to the question of transmission, the report says, "Scientific witnesses also considered that in future the electric current might be extensively used to transmit power as well as light to considerable distances," an opinion which the committee "only mention as showing the importance of allowing development to a practical application of electricity." We are not aware of any obstacle to such development, nor of any power of "altering" the same. As to the light itself, the committee report that," so far as its practical application has already gone, there seems to be no reason to doubt