Intelligence and Miscellaneous Articles. 145 



two fluorescent substances of the first class*, one of them charac- • 

 terized by the absorption-band 55 and orange-yellow fluorescence 

 (30 to 57), the other by the absorption-band 69 and yellow-green 

 fluorescence (57 to 70)t. 



2, Bisulfihobicliloranthracenous Acid. — The faintly brownish- 

 yellow-coloured etheric solution presents no absorption-bands, but 

 only a slight absorption of the blue and a stronger of the violet rays. 

 It fluoresces at its surfaces a very beautiful blue, from its interior 

 greenish. The spectrum of its fluorescence-light extends from 30 

 to 162, (therefore to the violet end), and shows four maxima — viz. 

 between 70 and 80, at 109, 131, and 150, of which the first three 

 appear about equally intense, the last somewhat less so. Between 

 these maxima are feebly marked minima to be perceived at about 

 98, 117, and 140. The fluorescent spectrum commences (faintly) 

 at about F, and extends, with an olive-greenish tone of colour and 

 slight intensity of light, up to about 150, here almost suddenly be- 

 comes a beautiful blue and very bright, attains its greatest bright- 

 ness, immediately before H, and reaches, with the same blue colour, 

 far iuto the ultra-violet. The fluorescence is of the second kind, 

 i. e. follows Stokes's rule. — Wiedemann's Annalen, 1879, No. 1, 

 pp. 115-118. 



ON THERMAL RADIATION AT HIGH TEMPERATURES. 

 BY J. L. SORET. 



In some researches the results of which I have previously made 

 public J, I arrived at the conclusion that Dulong and Petit's law of 

 thermal radiation ceases to be found true at very high temperatures. 

 Since then I have made, according to other methods, a few similar 

 experiments, which [ have not yet published, because I wished to 

 complete and render them more exact. Long ago I spoke of them 

 to M. Eaoul Pictet, who, now engaged in a critical investigation on 

 solar heat, has asked me for some information on the subject ; and 

 this has induced me to give the following compendious summary of 

 those experiments, imperfect as they are. 



"When an electric current is caused to pass through a conducting 

 wire, the temperature of the wire rises until the heat which it loses 

 by radiation, by contact with the air, and by conductivity at the 

 points of attachment becomes equal to the heat evolved in its inte- 

 rior by the electricity. We can, on the one hand, estimate this last 

 quantity of heat, and, on the other, by estimating the temperature 

 taken by the wire, calculate the quantity of heat which it ought to 

 emit according to the law of Dulong and Petit. 



* Compare Wied. Ann. iii. p. 125 (1878). 



t In accordance with the theory (see AVied. Ann. iii. p. 251, 1878), 

 each of these two parts of the fluorescence-spectrum would represent the 

 emission-spectrum belonging to the corresponding absorption-bands dis- 

 placed somewhat downwards, or each of the two absorption-bands would 

 have to be regarded as the " reversal " of the fluorescence-band belonging 

 to it. 



\ Archives cles Sciences Fhys. et Xaiurelles, 1872, t. xliv. p. 220, t. xlv 

 p. 252 ; 1875, t. Iii. p. 89 &c. : 1876, t. lv. p. 217. Phil. Ma?. [TV.] vol. L 

 p. 155 (1875). 



