42 Dr. C. K. Akin on Calcescence. 



oxyhydrogen-jet* or by electricity might be preferable to lime- 

 light for the experiments here spoken of. Coke made incandes- 

 cent by electricity, or the so-called electric light, presents, with 

 regard to the other sources of rays just mentioned, the follow- 

 ing further advantages : — (1) According to Prof. Stokes the spec- 

 trum of electric light is much more extended in the direction of 

 the Ritteric rays than the solar spectrum f. Now, according to 

 Prof. Draper's observations, the higher the maximum refrangi- 

 bility of the rays emitted by any incandescent solid substance, 

 the higher is its temperature, and the greater also is the inten- 

 sity of the rays of lower refrangibility J. Hence it might seem 

 probable that the joint intensity of the Herschellic radiations 

 emitted by the electric light are greater than those of the 

 similar radiations emanating from equal parts of the sun§. (2) 

 The temperature of the electric light, or of the coal points 

 by means of which it is produced, is considered to be higher 

 than that of the oxyhydrogen-ilame, and consequently also 

 higher that that of lime-light ||. I had frequently desired to test 

 the transmitting powers of the various diaphragms before men- 

 tioned by the aid of the electric lamp, but I had no opportunity 

 of carrying out my design %, 



(hi) Other subjects of experiment, which suggested themselves 

 to me from their relation to the principal subject-matter of this 

 paper, I shall point out here very briefly. 



(1) One of the first questions which arose in my mind in con- 

 nexion with the explanation of the phenomena of lime-light, 

 &c, was whether in consequence of the ray-transmutations 

 therein taking place the total emission of rays was altered. I 

 later found that Melloni had long ago shown such to be the case 

 in instances where the transmuting agent is a solid. M. Mag- 

 nus, recently, has shown that the same result obtains also in 



* According to M. E. Becquerel, however, " coke placed in the flame of 

 the oxyhydrogen blowpipe emits a light but little different from that of a 

 piece of magnesia or lime" (Ann. de Chim. et de Phys. 1863, vol. lxviii. 

 p. 139. 



t Proc. Roy. Inst. vol. i.p. 264 (1853). 



X Phil. Mag. vol. xxx. p. 345 (1847). 



§ Compare, however, the experiments of MM. Fizeau and Foucault in 

 Comptes Rendus, vol. xviii. p. 746 (1844) ; and of MM. De la Provostaye 

 and Desains, ibid. vol. xxxi. p. 515 (1850). 



|| See M. E. Becquerel, loc. cit. pp. 137 & 139. 



% I have reason to know that, within the last month or so, experiments 

 have been made at the Royal Institution on calcescence, by means of the 

 electric lamp, holding out great promise of success. It is stated that ignited 

 magnesium wire, which emits a light of great brilliancy, is rather deficient 

 in radiations of comparatively low refrangibility ; otherwise a magnesium- 

 wire lamp would offer great advantages as to convenience over any of the 

 other sources of rays above mentioned. 



