C. GENERAL PHYSICS. 75 



maximum, and the tension of the current is exerted to its ut- 

 most in passing through the non-conducting medium. This 

 assumption of the polarization of the medium between the 

 electrodes, and its consequently diminished power of conduct- 

 ing the current, seems to be somewhat sustained by the fact 

 that a powerful electro-magnet, in the form of a horseshoe, 

 when approached, did not extinguish the light, although it 

 produced rotation of the current ; for we may conceive that 

 the two poles, acting simultaneously on the medium, would 

 each neutralize the effect of the other. ID, May, 1872,299. 



BOYDEN PREMIUM. 



Uriah A. Boyden, of Boston, has deposited with the Frank- 

 lin Institute, of Philadelphia, the sum of one thousand dollars, 

 to be awarded as a premium to any resident of North Ameri- 

 ca who shall determine by experiment whether all rays of 

 light, and other physical rays, are or are not transmitted 

 with the same velocity. The conditions of the premium limit 

 the applicants to those living north of the southern boundary 

 of Mexico, and including the West India Islands. Applica- 

 tions must be made before the 1st of January, 1873, at which 

 time the judges, appointed by the Franklin Institute, shall 

 examine the memoirs and decide whether any one is entitled 

 to the premium. 1 D, January, 1872. 



ACTION OF LIGHT IN ELIMINATING OXYGEN FROM PLANTS. 



In the course of some experiments recently prosecuted by 

 Miiller on the action of light of different degrees of refrangi- 

 bility upon the elimination of oxygen from the green portions 

 of plants, it was ascertained that the curve of intensity for 

 the assimilating action of the different rays possesses several 

 maxima, and that the highest intensity of the secretion of 

 oxygen lies in the red of the spectrum, between the Fraun- 

 hofer lines B and C, or in that part of the spectrum the rays 

 of which are most completely absorbed by both living and 

 dead chlorophyl. 19 (7, January 20, 1872, 18. 



YOUNG ON THE SPECTROSCOPE. 



Number 109 of Nature contains an article, in detail, by 

 Professor Young, of Dartmouth College, upon the construc- 

 tion, arrangement, and best proportion of the spectroscope 



