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this is to become thoroughly acquainted with the difference be~ 

 tween the inclination at two different hours of the day. In this 

 way 1 hope to lind the means of controlling the results which 

 perhaps 1 mav some day be able to obtain for each of the 

 twenty-four hours of the day by means of the magnetographs. 

 Until now it has been impossiblc to have the magnetographs 

 in working order for want of an appropriate building. 



Batavia, Dec. 24 th 1869. 



