Intelligence and Miscellaneous Articles. 409 



observed (Phil. Mag., S. 3. vol. i. p. 8), a " surprising discre- 

 pancy," so great indeed as to be quite "alarming." After re- 

 marking the difficulty of finding any explanation of it, Sir 

 David concludes that it must arise from the different refrac- 

 tive powers possessed by different specimens. But though this 

 cause must operate in some degree, we cannot tell to what ex- 

 tent it is effective, and the discrepancy may notwithstanding 

 be occasioned, in a great measure, by a deviation from the 

 Huyghenian law. The whole question must therefore be re- 

 opened, and the ordinary indices for the fixed lines of the 

 spectrum must be determined by means of different prisms 

 cut out of the same piece of Iceland spar. 



Whatever the result may be, whether it shall confirm the 

 law of Huyghens, or show that another must be substituted 

 for it — it will at least be useful for science, by removing the 

 uncertainty in which the subject is at present involved. 

 Trinity College, Dublin, Sept. 24, 1842. 



ATOMIC WEIGHTS OF ELEMENTS. 

 MM. Marchand and Erdmarm are at present engaged in a series 

 of researches which seem to prove that Prout's idea that all atomic 

 weights are multiples of that of hydrogen, is correct. They have 

 as yet examined only the following bodies : — 

 Oxygen. . = 100' 1 



Hydrogen = 12*5 



Carbon . . = 75* 6 



Nitrogen =175* 14 



Calcium . . = 250 . . . . 20 



Chlorine . . = 450 36 



Silver .... = 1250 .... 100 



Lead = 1300 .... 104 



Extract from a letter from Berlin addressed to W. Francis. 



ON A VERY CURIOUS FACT CONNECTED WITH PHOTOGRAPHY, 

 DISCOVERED BY M. MCSSER OF KCSNIGSBERG, COMMUNICATED 

 BY PROF.BESSEL TO SIR D. BREWSTER*. 



Sir D. Brewster said, he was requested to communicate an account 

 of some remarkable facts connected with the theory of photography. 

 A new process of producing photographic impressions had been disco- 

 vered by Dr. Moeser of Kcenigsberg ; and an account of the discovery 

 had been brought to this country by Prof. Bessel, who received it from 

 the discoverer himself. The subject was most important, and it would 

 have been a great misfortune if the Physical Section had separated 

 without being made acquainted with it. The following were the 

 general facts connected with it : — A black plate of horn, or agate, is 

 placed below a polished surface of silver, at the distance of one-twen- 

 tieth of an inch, and remains there for ten minutes. The surface of 



* From the Report of the proceedings of the British Association, Man- 

 chester, June 29, 1 842. — Athenaeum, No. 770. See Dr. Draper's letter on 

 the subject at p. 348 of the present Number. 



Phil. Mag. S. 3. Vol. 21. No. 139. Nov. 1842. 2 E 



