484 Intelligence and Miscellaneous Articles, 



sure of the amount of action effected by the light. The diminution 

 in volume of the gas measui'ed by the rise of water in a graduated 

 tube was found to be regular, proving that when the light is constant 

 the amount of action is directhj proportional to the time of exposure. 



The relation between the amount of action and the amount of 

 light was experimentally determined, by allowing known quantities 

 of diffuse light to fall upon the sensitive gas. Experiments thus 

 conducted showed that the amount of action is directly proportional 

 to the amount or intensity of the light. These simple relations 

 were observed by Dr. Draper, of New York, in 1843, but his 

 method of experimenting differed essentially from that employed in 

 these researches, and was not susceptible of any very great degree of 

 accuracy. The relation between the amount of action and the mass 

 of the sensitive gas has not as yet been fully determined ; experi- 

 ment has however already shown that the relation is not a simple one. 



Many very interesting phsenomena were observed in the course 

 of these investigations. When the gas is first exposed to the light 

 no action whatever is observed ; after a short time the absorption 

 slowly begins, and increases until a maximum has been attained, 

 after which it proceeds regularly. This phsenomenon of induction 

 probably depends on a peculiar allotropic change which the chlorine 

 must undergo before it is capable of uniting with the hydrogen. 



I'he speaker concluded by expressing his intention of continu- 

 ing these experiments at Heidelberg, in order exactly to determine 

 the relation which exists between the amount of action and the 

 volume of gas employed; to investigate the phenomenon of induction; 

 and to obtain, if possible, an absolute measure for the chemical rays. 



LXIII. Intelligence and Miscellaneous Articles. 



ON SOME OF THE PRINCIPAL CAUSES OF ATMOSPHERIC 

 ELECTRICITY. BY M. BECQUEREL. 



^■"^HE causes which constantly furnish the air with an excess of 

 X positive and the earth with an excess of negative electricity, 

 excesses which are capable of giving rise to storms and other phse- 

 nomena under certain conditions, are still unknown, notwithstand. 

 ing the endeavours of physicists to discover them. 



In studying this question some years ago I observed the electrical 

 effects produced in the tissues of plants, and at the contact of these 

 plants with the soil ; in this contact the soil is constantly positive 

 and the plant negative, whatever may be the part of the plant put 

 in metallic communication with it. I then indicated this evolution 

 of electricity as one of the causes of the electricity of the atmosphere. 

 In repeating these experiments a year ago, I was struck by the 

 anomalies manifested, in operating on the margin of a river, or in 

 the river itself, or at a certain distance, near the plant, and I was thus 

 led to study the electrical effects produced at the contact of the soil 

 with a fall or stream of water, of which I then understood all the 

 importance. In last October I communicated to the Academy the 

 first results of my experiments, and I have since been constantly 

 occupied with this question, which leads us to one of the principal 

 sources of atmospheric electricity, — a question of a most compli- 



