Intelligence and Miscellaneous Articles. 159 



M. Lecoq de Boisbaudran, in 1871, pointed out that, in the spectrum 

 of a metal, the higher the temperature of the source, the nearer is 

 the brightest hue to the ultra-violet ; andhe showed that a certain line 

 in the vicinity of the infra-red, visible at one temperature, ceases 

 to be so at a higher temperature, and that then some lines towards 

 the ultra-violet become visible which at first were not so. MM. 

 Briinner and Salet have remarked that hydrogen and a certain 

 number of metalloids gave different spectra when the nature of the 

 sources was different. 



Having been permitted to take advantage of the resources of the 

 laboratory under the direction of M. Desains at the Sorbonne, I 

 proposed to myself (1) to determine the distribution of the heat in 

 the calorific spectrum produced by a Bourbouze lamp and a re- 

 fracting system of flint glass, (2) to study the variations of this 

 spectrum with the temperature of the source, and (3) to observe 

 also the absorption-spectra of various bodies, and their variations 

 with the temperature of the source. 



In all my experiments the apparatus preserved its initial posi- 

 tion throughout. 



The lamp employed is formed essentially of a Bunsen's burner sur- 

 mounted by a cylinder of sheet platinum closed at the top. In 

 this cylinder the combustion took place of illuminating-gas and of 

 air supplied by a tromp, the tension of this air being measured by 

 a manometer. To secure different fixed temperatures it was suffi- 

 cient to vary the tension of the air arriving at the lamp, and to 

 bring to the latter the quantity of gas requisite to give it the maxi- 

 mum of brightness, which always corresponds to its minimum of 

 sonorousness. At that instant the combustion appears to take 

 place in the cylinder only. 



To estimate the various temperatures a thermoelectric actinome- 

 ter is placed at a distauce of 65 centims. from the lamp. The tem- 

 peratures are not measured, but defined by the difference between 

 the positions of equilibrium of the needle of the galvanometer 

 when the actinometer receives and when it does not receive the 

 heat of the source. 



These different sources, viewed in the spectroscope with a prism, 

 give continuous spectra. 



In my experiments I have operated sometimes by the usual 

 method of impulsions, sometimes by a different method (in which 

 definite positions of equilibrium only are observed). I shall sub- 

 sequently return to this new manner of operating. Eor the pre- 

 sent I confine myself to indicating a few results. 



I readily perceived at the commencement that the maximum ap- 

 proaches the least-refrangible part of the spectrum in proportion as 

 the temperature of the source is lowered. I saw moreover that in 

 this case the curves representing the results glide, without losing 

 their form, in the same direction as the maximum. 



I next divided the spectra to be studied into four portions, de- 

 fined by the angular distances from the extreme red to their limits; 

 and taking the ratios of the quantities of heat of each of these 

 parts to the total quantity of heat of the spectrum under conside- 

 ration, I obtained the results recorded in the following Tables. 



