THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



NOVEMBER 1864 



XXXIX. On Luminous and Obscure Radiation. 

 By John Tyndall, F.R.S., $c* 



1. CIR WILLIAM HERSCHEL discovered the obscure rays 

 ^~J of the sun, and proved that the position of maximum 

 heat was beyond the red of the solar spectrum t- Forty years 

 subsequently Sir John Herschel succeeded in obtaining a thermo- 

 graph of the calorific spectrum, and in giving striking visible evi- 

 dence of its extension beyond the red J. Melloni proved that an 

 exceedingly large proportion of the emission from a name of oil, 

 of alcohol, and from incandescent platinum heated by a flame of 

 alcohol, is obscure §. Dr. Akin inferred from the paucity of lumi- 

 nous rays evident to the eye, and a like paucity of extra-violet rays, 

 as proved by the experiments of Dr. Miller, that the radiation 

 from a flame of hydrogen must be mainly extra-red ; and he con- 

 cluded from this that the glowing of a platinum wire in a hy- 

 drogen-flame, as also the brightness of the Drummond light in 

 the oxyhydrogen-flame, was produced by a change in the period 

 of vibration ||. By a different mode of reasoning I arrived at the 

 same conclusion myself, and published the conclusion subse- 

 quently^. 



2. A direct experimental demonstration of the character of the 

 radiation from a hydrogen-flame was, however, wanting, and this 

 want I have sought to supply. I had constructed for me, by 

 Mr. Becker, a complete rock-salt train of a size sufficient to 



* Communicated by the Author, 

 t Phil. Trans. 1800. 



X Phil. Trans. 1840. I hope very soon to be able to turn my attention 

 to the remarkable results described in Note III. of Sir J. Ilerscliel's paper. 

 § La Thermochrose, p. 304. ^ Phil. Trans, vol. cliv. p. 327. 



|| Reports of the British Association, 1863. 



Phil. Mag. S. 4. Vol. 28. No. 190. Nov. 1864. Z 



