1856.] Report on the Magnetic Survey. 559 



Meteorology. 



In Assam, observations were made on the variations of the tem- 

 perature of the Brahmaputra, from Debrooghur to its ramifications 

 in the Delta, a subject of particular interest. Also, besides the regu- 

 lar observations on the temperature, moisture, and pressure of the air, 

 I made several experiments on the thermic influence of surfaces 

 covered with grass and tree jungle ; and Dr. Simmons, at Growhatty, 

 kindly assisted me during my absence, by making observations on 

 the ozone contained in the air, with papers identical with those 

 used by myself. 



These observations are being continued for the next year. 



The following Table contains* the temperature found in the 

 Brahmaputra, in its ramifications, and in the Delta, from Debroo- 

 ghur to Calcutta. The daily variations, even in Upper Assam, 

 scarcely exceeded 0.5 degrees C. =0.9 degrees F., but occasionally 

 differences of 2 to 3 degrees F. are found even in the Yery current, 

 caused in some cases by differences of depth, in others by lateral rivers 

 discharging themselves into the Brahmaputra. 



I choose for the Table the temperature of the rivers at 11a. m., 

 this hour representing very nearly the mean of the twenty-four 

 hours for the water ; for the temperature of the air for the same 

 reason the temperature at 9 a. m. is selected. Errors of the zero 

 points of the Thermometers Nos. 29, 70 and 88 are corrected.f 



* A second series during the hot season is now being made by my Assistant, 

 Mr. Adams, on his way down from Sudiya. 



t For the Hooghly, at Calcutta, I was furnished with observations on the 

 monthly variations of the temperature at high and low water by the kind assist- 

 ance of Mr. Schiller. The observations are now being continued by Dr. Thomson. 



