39 2 



NATURE 



\Augiist 24, 1882 



great prooriety, I think, he called the Joule, after the man who 

 lias done so much to develop the dynamical theory of heat. 



Professor Clausius urges the advantages of the statical system 

 of measurement for simplicity, and shows that the numerical 

 values of the two systems can readily be compared by the intro- 

 duction of a factor, which he proposes to call the critical velocity ; 

 this, Weber has already shown to be nearly the same as the 

 velocity of light. It is not immediately evident how by the in- 

 troduction of a simple multiple, signifying a velocity, the statical 

 can be changed into dynamical values, and I am indebted to my 

 friend Sir William Thomson for an illustration which struck me 

 as remarkably happy and convincing. Imagine a ball of con- 

 ducting matter so constituted that it can at pleasure be caused to 

 shrink. Now let it first be electrified and left insulated with 

 any quantity of electricity on it. After that, let it be connected 

 with the earth by an excessively fine wire or a not perfectly dry 

 silk fibre ; and let it shrink just so rapidly as to keep its poten- 

 tial constant, till the whole charge is carried off. The velocity 

 with which its surface approaches its centre is the electrostatic 

 measure of the conducting power of the fibre. Thus we see 

 how "conducting power" is, in electrostatic theory, properly 

 measured in term; of a velocity. Weber had shown how, in 

 electromagnetic theory, the resistance, or the reciprocal of the 

 conducting power of a conductor, is properly measured by a 

 velocity. The critical velocity, which measures the conducting 

 power in electrostatic reckoning and the resistance in electro- 

 magnetic, of one and the same conductor, measures the number 

 of electrostatic units in the electromagnetic unit of electric 

 quantity. 



Without waiting for the assembling of the International Com- 

 mittee charged with the final determination of the Ohm, one of 

 its most distinguished members, Lord Rayleigh, has, with hi, 

 collaborateuse, Mrs. Sidgwick, continued his important investi- 

 gation in this direction at the Cavendish Laboratory, and has 

 lately placed before the Royal Society a result which will pro- 

 bably not he surpassed in accuracy. His redetermination brings 

 him into close accord with Dr. Werner Siemens, their two 

 values of the mercury unit being 0"954iS and C9536 of the 

 B.A. unit respectively, or I mercury unit=o'94i3 X io 9 C.G.S. 

 uni's. 



Shortly after the publication of Lord Rayleigh's recent re ults, 

 Messrs. Gla2ebrook, Dodds, and Sirgant, of Cambridge, com- 

 municated to the Royal Society two determinations of the Ohm, 

 by different methods ; and it is satisfactory to find that their 

 final values differ only in the fourth decimal, the figures being, 

 according to 



Lord Rayleigh ... I Ohm = 0-98651 ' ir ' v ua ' ran 



Messrs. Glazebrook, etc. =o - 9S6439 ,, 



Professor E. Wiedemann, of Leipzig, has lately called atten- 

 tion to the importance of having the Obm determined in the 

 mo-t accurate manner possible, and enumerates four distinct 

 methods, all of which should unquestionably be tried with a 

 view cf obtaining concordant results, because upon its accuracy 

 will depend the whole future system of measurement of energy 

 of whatever form. 



The word Energy was first used by Young in a scientific 

 serse, and represents a conception of recent date, being the out- 

 come of the labours of Carnot, Mayer, Joule, Grove, Clausius, 

 Clerk-Maxwell, Thomson, Stokes. Helmholtz, Macquorn- 

 Rankine, and other labourers, who have accomplished for the 

 science regarding the forces in Nature what we owe to Lavoi- 

 sier, Dalton, Berzelius, Liebig, and others, as regards Chemistry. 

 In this short word Energy we find all the efforts in nature, in- 

 cluding electricity, heat, light, chemical action, and dynamics, 

 equally represented, forming, to use Dr. Tyndall's apt expres- 

 sion, so many " modes of motion." It will readily be conceived 

 that « hen we have established a fixed numerical relation between 

 these different modes of motion, we know beforehand what is 

 the utmost result we can possibly attain in converting one form 

 of energy into another, and to what extent our apparatus for 

 effecting the conversion falls short of realising it. The differ- 

 ence between ultimate theoretical effect and that actually obtained 

 is commonly called loss, but, considering that energy is inde- 

 structible, represents really secondary effect which we obtain 

 without desiring it. Thus friction in the working parts of a 

 machine represents a loss of mechanical effect, but is a gain of 

 heat, and in like manner the loss sustained in transferring elec- 

 trical energy from one point to another is accounted for by heat 

 generated in the conductor. It sometimes suits our purpose to 



augment the transformation of electrical into heat energy at 

 certain points of the circuit when the heat nys become visible, 

 and we have the incandescence electric light. In effecting a 

 complete severance of the conductor for a short distance, after 

 the current has been establi-hed, a very great local resistance is 

 occasioned, giving rise to the electric arc, the highest develop- 

 ment of heat ever attained. Vibration is another form of lost 

 energy in mechanism, but who would call it a loss if it proceeded 

 from the violin of a Joachim or a Norman-Neruda ? 



Electricity is the form of energy best suited for transmitting 

 an effect from one place to another ; the electric current passes 

 through certain substances — the metals — with a velocity limited 

 only by the retarding influence caused by electric charge of the 

 surrounding dielectric, but approaching probably under favour- 

 able conditions that of radiant heat and light, or 300,000 kilo- 

 metres per second ; it refuses, however, to pass through oxidised 

 substances, glass, gums, or through gases except when in a 

 highly rarefied condition. It is easy therefore to confine the 

 electric current within bounds, and to direct i'. through narrow 

 channels of extraordinary length. The conducting wire of an 

 Atlantic cable is such a narrow channel ; it consists of a copper 

 wire, or strand of wires, 5 mm. in diameter, by nearly 5,000 

 kilometres in length, confined electrically by a coating of gutta - 

 percha about 4 mm. in thickness. The electricity from a small 

 galvanic battery passing into this channel prefers the long 

 journey to America in the good conductor, and back through 

 the earth, to the shorter journey across the 4 mm. in thickness 

 of insulating material. By an improved arrangement the alter- 

 nating currents employed to work long submarine cables do not 

 actually complete the circuit, but are merged in a condenser at 

 the receiving station after having produced their extremely slight 

 but Gertain effect upon the receiving instrument, the beautiful 

 syphon recorder of Sir William Thomson. So perfect is the 

 channel and so precise the action of both the transmitting and 

 receiving instruments employed, that two systems of electric 

 signals may be passed simultaneously through the same cable in 

 opposite directions, producing independent records at either end. 

 By the application of this duplex mode of working to the Direct 

 United States ctble under the superintendence of Dr. Muirhead, 

 its transmitting power was increased from twenty-five to sixty word; 

 a minute, being equivalent to about twelve currents or primary 

 impulses per second. In transmitting these impulse-currents 

 simultaneously from both ends of the line, it must not be 

 imagined, however, that they pass each other in the manner of 

 liquid waves belonging to separate systems ; such a supposition 

 would involve momentum in the electric flow, and although the 

 effect produced is analogous to such an action, it rests upon 

 totally different grounds—namely, that of a local circuit at each 

 terminus being called into action automatically whenever two 

 similar currents are passed into the line simultaneously from both 

 ends. In extending this principle of action quadruplex tele- 

 graphy has been rendered possible, although not yet for Ion; 

 submarine lines. 



The minute currents here employed are far surpassed as regards 

 delicacy and frequency by those revealed to us by that marvel of 

 the present day, the telephone. The electric currents caused by 

 the vibrations of a diaphragm acted upon by the human voice, 

 naturally vary in frequency and intensity according to the number 

 and degree of those vibrations, and each motor current in 

 exciting the electro-magnet forming part of the receiving 

 instrument, deflects the iron diaphragm occupying the position 

 of an armature to a greater or smaller extent according to its 

 strength. Savart found that the fundamental la springs frcm 

 440 complete vibrations in a second, but what must be the fre- 

 quency and modulations cf the motor current and of magnetic 

 variations necessary to convey to the ear through the medium of 

 a vibrating armature, such a complex of human voices and of 

 musical instruments as constitutes an opera performance. And 

 yet such performances could be distinctly heard and even enjoyed 

 as an artistic treat by applying to the ears a pair of the double 

 telephonic receivers at the Paris Electrical Exhibition, when con- 

 nected with a pair of transmitting instruments in front of the 

 footlights of the Grand Opera. In connection with the tele- 

 phone, and with its equally remarkable adjunct the microphone, 

 the names of Riess, Graham Bell, Edison, and Hughes, will 

 ever be remembered. 



Considering the extreme delicacy of the currents working a 

 telephone, it is obvious that those caused by induction from 

 neighbouring telegraphic line wires would seriously interfere 

 with the former, and mar the speech or other sounds produced: 



