of Heat in the Prismatic Spectrum. 337 



Exp. 5. — Same prism ; distance from thermoscope four feet. 

 One inch and a half above the violet, by the \ -„ _j^,/, 



side of the spectrum J ^ 



One inch and an half ditto, in the spectrum ..55^ 



One ditto, ditto 5 5| 



Half ditto, remains 5 5| 



In the violet 6 2 



In ditto, and a little blue 6 9 



Thus again, in both experiments, an elevation of temperature 

 beyond the violet. However, it ought to be mentioned that 

 in frequent instances the thermoscope here showed no increase 

 of heat. 



Exp. 6. (22d September 1806.)— Another prism. No. 2; 

 distance of thermoscope from it two feet two inches. 



The prism exhibited the greatest heat outside of the spec- 

 trum, particularly at a quarter of an inch below the red *. 

 The difference between the station here and in the violet 

 amounted to four inches two lines. The spectrum itself was 

 very brilliant, the prism being one of the clearest and purest 

 that I ever used. This instrument, together with another of 

 similar size and perfection, is kept in the Duke's cabinet of 

 natural philosophy at Jena. The second prism was also found 

 similar in effect to the first. The specific gravity of these two 

 prisms is, according to M. Voigt of Jena, 3*2482, at 61°'25 F. 

 They are therefore of flint-glass, and, as I suspect, of English 

 manufacture. I must add that the two prisms are equilateral, 

 the breadth of each side being about one inch. 



I made with the prism No. 2, two other experiments (7th 

 and 8th) ; and all three as perfectly accorded with each other 

 as could be expected from experiments of this kind. The dif- 

 ference between the violet and the red, in the 6th experiment, 

 was four inches two lines; in the 7th, four inches one line; in 

 the 8th, four inches. The deviations in the difference between 

 the red and a quarter of an inch below it were greater ; for in 

 the first instance thirteen lines ; then, twice, nine lines ; and 

 hi the last case, eight lines. The mean of this would be nine 

 lines and three (juarters. That this shows the difference be- 

 tween the heat in the red, and a quarter of an inch below it, 

 lather below than above the truth, may be seen from the fol- 

 lowing experiments. 



Exjj. 9. — Distance from thermoscope seven feet, as in ex- 

 periments 7 and 8, and with a very clear sky. 



* The experiments were conducted like the former. It will, therefore, 

 be sufiicient here and henceforward only to mention the results. — Geuman 

 EurroR. 



Vol.66. Xo. 331. Nov. 1825. U u In 



