56o 



NATURE 



[January 20, 19 16 



some essential points. The advice to try always 

 to adjust the arc "by means of the series resist- 

 ance alone " is ambiguous. To adjust the arc 

 to normal length, and to adjust the arc to take 

 the correct current, are two different matters, and 

 require recourse to different means. 



There is an extraordinary dictum on p. 39 : — 

 "The close relation between the specific heat of 

 a luminous layer and the radiation thereof is 

 evident, since the eflficiency of a luminous body 

 increases rapidly with its temperature." This 

 betrays a strange confusion of thought. The 

 specific heat of a substance is indeed of import- 

 ance during the period when its temperature is 

 rising. But when the high temperature of in- 

 candescence has once attained its steady value, 

 the specific heat of a material has per se no more 

 influence on its efficiency of radiation than has its 

 price in the market. 



In dealing with Mrs. Ayrton's careful investi- 

 gation of the relations which subsist in the con- 

 tinuous current arc between arc length, current, 

 and potential difference across the arc, the author 

 is often obscure. He seems to have no grip of 

 the distinction between a dependent variable and 

 an independent one. Thus it appears from Mrs. 

 Ayrton's work that if a current of 10 amperes 

 is passed through an arc (using solid carbons) 

 5 millimetres long, the arc voltage is about 

 56 volts, and remains at that figure if length and 

 current are main-tained constant. Also that if a 

 current of 8 amperes is passed through an arc 

 •4" 5 millimetres long, the arc voltage is still 56 volts. 

 But though the voltage thus appears to be con- 

 stant, it does not follow that on a circuit main- 

 tained at 56 volts the current will adjust itself 

 to 10 amperes if the carbons are set to a distance 

 of 5 millimetres. On the contrary, assuming that 

 these values could be momentarily attained, the 

 current would at once increase a little, thereby 

 lowering the resistance of the arc, and with 

 lowered resistance the current would increase 

 still more, and the rush of current will be enor- 

 mous unless a steadying resistance is introduced 

 into the circuit. The phenomena are perfectly 

 well known-, but the interpretation might be more 

 clearly stated if it were plainly recognised that 

 the arc voltage is not an independent variable. 

 Incidentally the author points out that J. Stark 

 has shown that spark discharges of not too great 

 length follow a law of the same form as that 

 which Silvanus Thompson gave for the arc, 

 namely e = m + C/I; where m is the voltage for 

 minimum length and C the watts per ampere, 

 which for given materials is nearly constant. 



The author devotes several pages to the theory 

 NO. 2412, VOL. 96] 



of stability of the arc, and comes to the strange 

 conclusion that for every (carbon) arc there is a 

 maximum potential difference across the arc be- 

 yond which the arc will extinguish itself, namely 

 that which is exactly half-way between the mini- 

 mum voltage (about 36^ volts for carbon arcs) 

 and the voltage of supply. If this is true then 

 on loo-volt mains the maximum possible voltage 

 would be 6S\ volts, and the efficiency necessarily 

 limited to 68J per cent. Another strange con- 

 clusion is that the numerical values obtained by 

 Mrs, Ayrton for the carbon arc are valid only 

 in connection with the particular generator which 

 she used ! The author repeats, in the chapter on 

 the distribution of energy in the arc, the opinion 

 that for electrodes the substances used should 

 have a low specific heat, declaring this to be "a 

 physical quantity of paramount imporJ:ance on 

 the luminous efficiency " of glowing solids, and 

 saying that this accounts for the high eflficiency 

 of the osmium lamp. It is difficult to attach a 

 coherent meaning to this, or to the statement 

 (p. 124) that "when an arc increases in length its 

 cross-sectional area does not remain constant, as 

 Ohm's law presupposes." Why should Ohm's 

 law presuppose any such nonsense? The author 

 claims for Bremer in 1899 the utilisation of the 

 introduction into arc carbons of metallic salts 

 that colour the arc, and hints not obscurely that 

 he himself was the discoverer of this property 

 in 1892. He ignores the circumstance that Gau- 

 doin published accounts of this manufacture in 



1875- 



The author interpolates in the chapter on the 

 distribution of energy in the arc a diatribe against 

 Maxwell's electromagnetic theory of light — "a 

 theory long since exploded" — which "has never 

 been productive of the least progress in the theory 

 or technology of light generation." He lauds 

 Minkowski's four-dimensional theory of rela- 

 tivity. He sets up Weber as advocating 

 Newton's corpuscular theory of light, and claims 

 " as a matter of national pride " to point out that 

 the Germans W^eber and Planck have corrected 

 the inaccuracies of those who attempted to apply 

 Maxwell's theory to experimental facts. Every- 

 one who advocated the undulatory theory of light 

 was, it appears, wrong. 



"This strife could easily throw a dismal light 

 on the great of our nation. Blind animosity has 

 characterised this combat, surcharged with malice. 

 Even Goethe has taken part therein, as is evident 

 by the very way he mentions the name of 

 Newton." 



We can only ask, and in a double sense, is he 

 dead? 



