in the Magnetic Forces of the Earth. 



35 



o 



Curves showing the Mean Diurnal Variations of the Vertical Force, for quarters 



of years. 



Fig. 15. 



July, Aug. and Sept., 1841. 



22 Oh 



Fig. 16. 



Oct., Nov, and Dec, 1841. 



131 



1 



_j 



i j 









i 









- 













i i , 

















i 1 















\ i 









A t • j 







































IN 







T i i i 





i 1 



















i 







49 



155 



OA 2 4 6 8 10 12 14 16 18 20 23 Oh 



One division of magnetometer scale = -000033 vertical force. — Increase of num- 

 bers corresponds to decrease of force. 



Curves showing the Mean Diurnal Variations of the Difference between the Tem- 

 peratures of Philadelphia and Washington, for quarters of years. 



5° 



Fig. 18.... 

 H 17.... 



" 20.... 



" 19.... 



% 11, Jan., Feb. and March, 1842.— Fig. 18, April, May and June, 1841.— Fig. 19, 



July, Aug. and Sept., 1841.— Fig 20, Oct., Nov. and Dec. 1841. 



they have been carried, serve only to confirm the conclusion that 

 » is a general law that the difference of temperature, like the 

 vertical intensity, is greatest between the Lours of noon and 4 r. m., 

 and least about midnight. I conclude, therefore, that the diurnal 

 variations of the vertical intensity must be at least approximately 

 proportional to the diurnal variations of difference of temperature. 



