On the Light given off by a Phosphorescent Surface. 209 



supplies carried in by all the rivers of the globe. The ten- 

 dency of the operation going on upon the land is to reduce 

 the stock of carbon and increase that of carbonic acid, 



(1) by the combustion of coal and other substances used as 



fuel; 



(2) by the destruction of carbon accumulated near the sur- 



face of the soil by natural vegetation ; 



(3) by the increase of man and animals. 



On the other hand, there may be a corresponding increase of 

 organic carbon in the ocean, and in this way the balance may 

 be kept up. Dr. Frankland's various analyses of sea-water, 

 extending to a depth of between 700 and 800 fathoms, show 

 that even at this depth, which is less than half of the estimated 

 average, the amount of carbon, as organic carbon, is about 

 three times as much as the carbon, as carbonic acid, in the 

 atmosphere resting upon an equal area of surface. When we 

 consider the immensity of the ocean, it is evident that the 

 operations of animal and vegetable life in it must have a vast 

 influence upon our atmosphere, of the value of which we 

 appear to be altogether ignorant. 



XXVII. On the Rate of the Decrea.se of the Light given off by a 

 Phosphorescent Surface. By Lieut. L. Darwin, R.E.* 



I CARRIED out a series of experiments at Chatham with the 

 view of determining the law of the rate of decrease of 

 the light of a phosphorescent surface. The experiments were 

 conducted by comparing the light given off by a surface 

 covered with Balmain's luminous paint, with a sheet of tissue 

 paper illuminated from the further side by a Sugg's burner 

 regulated to give about the light of four standard candles. 

 The surface coated with paint was one side of a thin metal 

 vessel, which was filled with a mixture of ice and water ; the 

 object of this was to keep the temperature as uniform as 

 possible, as any increase of temperature increases the light 

 given off by the paint. A sheet of tissue paper, of about the 

 same size as the painted surface, was arranged just above it 

 so that the light of the burner illuminated the tissue paper 

 from the further side to the observer. The whole was en- 

 closed in a box with an opening at one side, through which 

 the light of the burner reached the tissue paper only, and 

 opposite to it a small hole through which the observations 

 were made. In this way only the light from the two surfaces 



* Communicated by the Physical Society. Read December 11th. 



