272 Scientific Intelligence. 



tried the class of experiments pointed out by Sir D. Brewster; but he 

 admitted their importance, and expressed a determination to pursue the 

 inquiry. — Prof. Grove inquired whether the experiments were tried 

 with the crystals placed in vacuo? — Prof. Pliicker replied no; but in 

 every case they were suspended either in air or in water. — Prof. Grove 

 pointed out the necessity of caution in that case, as it was well known 

 that differences between the diamagnetic actions of suspended bodies 

 and of the surrounding medium would sometimes mask and even re- 

 verse the action. — Prof. Faraday pointed out the precautions which had 

 been taken to avoid this source of error. 



2. On the Action of the Red, Orange and Yellow Rays upon Iodized 

 and Bromo-iodized Silver Plates, after they have been affected by Day' 

 light, and other Phenomena of Photography ; by M. Claudet, (Proc. 

 Brit. Assoc, Athen., No. 1086.)— It was shown by MM. E. Becquerel 

 and Gaudin, that a photographic image on a Daguerrotype plate might 

 be developed by the action of the light which permeates yellow and 

 red glasses, without the aid of mercurial vapor. M. Claudet has been 

 continuing his researches on this point, and he confirms those results 

 in a very striking manner. Numerous specimens were exhibited, in 

 which it was shown that the powers of the so-called continuativg rays 

 in developing the image were not much inferior to the mercurial vapor 



presenting a positive image like it, but difFering from it in the tint by 

 which it is suffused. M. Claudet suspects that this result is owing to 

 the decomposition of the iodid and bromo-iodid of silver by the least 

 refrangible rays — and that the whites are represented by finely-divided 

 silver in the place of mercury. The rate of action when the chemical 

 agency permeates these colored media is infinitely reduced for these 

 preparations ; but still it is evident that some of the photographic 

 principle permeates them — and also, that these rays which corres- 

 pond in color with those media have a peculiar scale of action of 

 their own. 



3. On the Influence of Light in preventing Chemical Action ; by 

 Mr. R. Hunt, (Proc. Brit. Assoc, Athen., No. 1086.)— Bearing on the 

 same subject as that brought forward by M. Claudet, although differing 



inasmuch as one set of experiments were made upon iodized silver 

 plates and the other upon iodized photographic paper, this subject was 

 taken by the Section before any discussion was allowed on the prece- 

 ding communication. Mr. Hunt having called attention to several ex- 

 periments in which certain luminous rays ha* been found to protect 

 photographic agents from chemical change— particularly in the re- 

 searches of Sir John Herschel, — proceeded to describe his own expe- 

 rimental investigation of this subject. Taking a piece of highly sensi- 

 tive photographic paper, which would blacken in a few seconds by the 

 light of an argand gas burner, he threw upon it a condensed spectrum 

 which had been previously analyzed by a peculiar yellow medium 

 and then, by means of a mirror, reflected the strong light of the sun 

 upon the paper. It was, therefore, under the influence of*the unalter- 

 ed reflected radiations — and also of the spectrum, from which the 

 chemical agency had been as nearly as possible separated. The re- 

 sult was, that the paper was blackened over every part except that por- 

 tion upon which the strong line of spectral light fell, which was protected 





