20 Report on the Magnetic Survey, [No. 1. 



Black vegetable earth, 527 



Quartz sand, . . . . i 447 



Grass, 71B 



Dark grey slate, 233 



Winds. 



As an observation of a more general nature, I may mention that 

 in Sikkim North winds are scarcely ever observed at heights below 

 10,000 feet, the large central masses protecting at a remarkable 

 distance the lower ranges to the South of them. 



In the valley of the Brahmaputra a regular daily variation takes 

 place, particularly in the cold season. 



During the day East and North-East winds follow the main direc- 

 tion of the valley, in the night South winds descend (which are the 

 prevailing winds in the Naga, Khosia, and Garrow mountain ranges) 

 into the valley of the Brahmaputra, after the ascending current has 

 ceased. The Southerly wind does not follow immediately after sun- 

 set, but much later, from 9 to 10 p. m. This discordance in time 

 seems to show that this phenomenon is caused to a great extent by 

 the cessation of the ascending current in the lower part of the course 

 of the Brahmaputra, where, during the day, an ascendant current is 

 originated over a much larger surface. The daily variation of the 

 barometer is decidedly affected by these changes in the currents of 

 the air. 



Composition of the atmosphere. 



1. — Experiments have been made about the quantity of carbo- 

 nic acid contained in the atmosphere, which increases decidedly at 

 great heights and shows remarkably great variations in regions ac- 

 cessible to clouds rapidly ascending from the plains. 



2. — Iodized papers (got directly from Prof. Schonbein) were re- 

 gularly used for getting the measurement of ozon. At Darjiling, Cal- 

 cutta, and Gowhatty continuous observations were made. In the 

 plains, particularly in jheels, we found the colouration of the paper 

 (the number increasing with the increase of ozon) to be 1 to 1.5 ; 



at Darjiling . June, day 4.5 night 7.1. 

 July „ 3.3 „ 4.8. 



