482 Presents. [Dec. 21, 



obtained with the less brilliant source of light. For Nos. I, II, and 

 III, photographs were taken, which gave the red and infra-red 

 spectrum, as well as the more refrangible end. With every number 

 ordinary gelatin plates of great sensitiveness were employed as a 

 check on the collodion plates. To the eye, the red, in each case, 

 extends a trifle more towards D than in the photograph. 



An attempt was made to produce the same range of photographic 

 action in the spectrum of the thicker solutions as in the less dense, by 

 increasing the time of exposure. The result, however, was abortive, 

 and hence we may conclude that when any visible ray is quenched to 

 sight by a solution of particular density, it also ceases to be photo- 

 graphically active. 



The last ray to disappear in the blue lies somewhere close to h, and 

 it will be seen that the ultra-violet rays are absorbed before the 

 absorption touches the violet. By using a still denser solution than 

 No. V, we were able to entirely quench the blue, both visually and 

 photographically, while the extreme red was still visible, and the 

 photograph taken showed no si^ns of absorption of the infra-red rays. 



In conclusion we would remark, that by tbe use of this solution in 

 a rock-salt cell and a grating, the infra-red spectrum from X 7,600 to 

 X 15,200 may be photographed without the instrumental separation of 

 the different orders of spectra ; and the conditions of our climate are 

 such that the atmospheric absorption usually, if not always, prevents 

 a study of the solar spectrum below the greater wave-length above- 

 named. 



Presents, December 21, 1882. 



Transactions. 



Bern: — Naturforschende Gesellschaft. Mittheilungen. 1881. Heft 2. 

 8vo. Bern 1882. ' The Society. 



Bologna : — Accademia delle Scienze dell' Istituto. Memorie. Serie 

 4. Tomo II. 4to. Bologna 1880. Accademia delle Scienze dello 

 Istituto di Bologna dalla sua Origine a tutto il MDCCCLXXX. 

 8vo. Bologna 1881. The Academy. 



Brussels : — Academic Royale de Medecine. Bulletin. 3e Serie. 

 Tome XVI. Nos. 4-9. 8vo. Bruxelles 1882. Memoires 

 Couronnes. Tome VII. Fasc. 2, 3. 8vo. Bruxelles 1882. 



The Academy. 



Societe Royale Malacologique. Annales. Tome XIII. 8vo. 

 Bruxelles 1878. Proces-Verbaux, Juin-Decembre, 1881. 8vo. 



The Society. 



Budapest : — Kon. Ungarische Geologische Anstalt. Mittheilungen. 

 Band VI. Heft 2. 8vo. Budapest 1882. The Institution. 



