236 Caricography. 



inversely proportional to its degree of refrangibility. Therefore, if 

 we employ in the construction of a prism a substance less active than 

 common glass, the loss will be weakened in greater proportion for 

 the less refrangible rays ; the latter will gain then upon the more re- 

 frangible rays and the maximum will advance in a direction opposite 

 to the preceding, that is, from the violet to the red. This is pre- 

 cisely what Herschel, Davy, and Seebeck ascertained in operating 

 with prisms of flint glass. 



Let us compare these effects with the numbers which represent 

 calorific transmissions : we shall find that the maximum of heat, in 

 leaving the yellow where it is found to be in the water prism, always 

 advances in the same direction, just as the prism is constructed of 

 substances more and more diathermous. It lies a little beyond the 

 spectrum when flint is substituted for crown glass. Admitting then 

 the exactitude of this theory, the line of the greatest heat must be 

 disengaged entirely from color and be found in the dark space much 

 beyond the red, when rock salt is used, a substance which is as 

 much more diathermous than flint, as flint is than crown glass. 



This important verification was made by the author on spectra 

 formed by five prisms of rock salt from different localities. It was 

 completely successful. In every case the maximum was found in 

 the dark space at a distance from the last luminous band equal to 

 that which exists on the opposite side between the greenish blue and 

 the limits of the red. 



Melloni has proved also that crystallized bodies act upon rays of 

 heat in the same manner in all directions. He has assured himself 

 of this by making the calorific radiation pass through prisms and 

 plates of the same thickness cut out of the same crystals in differ- 

 ent directions relative to the axes of crystallization. — Bib. Univ. 

 Oct. 1833. 



Art. VI, — Caricography ; by Prof. C. Dewey. 



Appendix, continued from Vol. xxvi. p. 378. 



No. 137. Carex saxatilis, L. 



WiUd. Sp. PL 4. page 272, and Pursh, No. 23. 



Schk. Tab. I and Tt. fig. 40. Wahl. No. 140. 



Spiels distinctis, staminifera solitaria, fructiferis distigmaticis sub- 



ternis oblongis obtusis sessilibus, inferiore pedunculata cum bractea 



