1856.] Report on the Magnetic Survey. 19 



The surface of the slate was found 100.54 square centimeters, the 

 boxes on an average 101.75 square centimeters, varying only be- 

 tween 101.70 and 101.80 square centimeters. 



The temperature of the air was 



Dry bulb. Wet bulb. 



October 28th 6 p. m 15.6 13.6 



October 28th 10 p. M 13.6 11.8 



October 28th to 29th, minimum, 12.9 



October 29th, 6 a. m 14.4 14.2 



Therefore the gramme of dew (distilled) water may be considered 

 equal to one cubic centimeter without any correction for the change 

 in the volume of water by temperature. The weight of the dew 

 deposited is, after the reduction to 100 square centimeters ; — 



grammes. 



For No. 2.— Black wool, „ 3.78 



3.— White wool, 3.63 



4. — Black vegetable earth, , 2.01 



5. — Quartz sand, 1.68 



6.— Grass, 2.72 



7. — Dark grey slate, 0.90 



Which gives the following thickness of the deposited stratum of 

 water in millimeters and decimals of millimeters and in decimals of 

 the English line (.1 inch) ; — 



M. M. Lines. 



For No. 2.— Black wool, 0.38 0.150 



3.— White wool, , 0.36 0.142 



4. — Black vegetable earth, 0.20 0.079 



5. — Quartz sand, 0.17 0.067 



6.— Grass, 0.27 0.107 



7.— Dark grey slate, 0.09 0.035 



The radiating power may be considered as proportional to the 



quantity of water deposited. Making the quantity deposited on the 

 black wool 1000, we get the following numbers corresponding to the 

 different radiating powers. 



Black wool, . . . c 1000 



White wool, ggO 



d 2 



