264 Professor Dewar [Jan. 16, 



In these experiments, the total nitrogen estimated by the mercury 

 process was almost identically the same as the amount of nitrogen 

 obtained by a very careful dilution of the acid in a large quantity of 

 water and titration with permanganate, proving that the main product 

 was nitrous anhydride, which may be explained by the fact that the 

 quantity of oxygen in presence of nitrogen in the immediate neigh- 

 bourhood of the poles is greatly diminished by the combustion of the 

 carbons, or that the nitric peroxide formed is subsequently reduced 

 by contact with the red hot carbon, or other reducing products. 



It is thus proved the carbon, nitrogen, oxygen, and hydrogen being 

 present at the temperature of the electric arc, the compound sub- 

 stances hydrocyanic acid, acetylene, and nitrous acid are invariably 

 formed. 



Radiation Experiments. 



In a report to the British Association * on the determination of 

 high temperatures in the year 1873, it was experimentally proved 

 that the law of Dulong and Petit could not be used as a basis for the 

 estimation of high temperatures, seeing that it " gives a far too rapid 

 increase for the total radiation." It was further observed that the value 

 of the radiation emitted by the same substance at different temperatures 

 expressed in terms of the thermo-electric current increase of intensity, 

 plotted in terms of the temperature, represented a " parabolic curve." 

 Assuming the general accuracy of this law for high temperatures, the 

 total radiation may be taken as nearly proportional to the square of 

 the temperature. From this law the hypothetical temperature of the 

 sun was " estimated as at least 11,000 C." Rosetti has recently made 

 a more elaborate investigation on the subject, and has arrived inde- 

 pendently at a formula of a parabolic order. Rosetti f represents his 

 results by the equation — 



M = a T* (T - 0) - 6 (T - 0), 



where /x is the total radiation measured by intensity of thermo- 

 electric current, T° the absolute temperature of the source, 6^ that of 

 the medium surrounding the pile, and a and h constants. However 

 well this formula may represent the complete series of the experi- 

 ments, it is certain that his results for temperatures above 150° may 

 be expressed within the limits of probable error as proportional to the 

 square of the temperature. To be convinced of this, it is sufficient to 

 plot the logarithm of the respective values of the radiation and tem- 

 perature, when it will be found the results arrange themselves in a 

 straight line, the tangent of which may be 1 • 9 or 2 for the observa- 

 tions above 150°. Experiments made with the thermopile, surrounded 

 with an annular vessel, through which a continuous current of water 



* Eeport of the Committee for determining High Temperatures by means of 

 the Refrangibility of the Light evolved by Fluid or Solid Substances. Bradford, 

 1873. Page 461. 



t " Rechcrches Expe'rimentales sur la Temperature du Soleil " (Accad. R. del 

 Liuuei. 1877-78), 



