LINES OF EQUAL HORIZONTAL FORCE. 7v> 



is in the proportion of 29 to 30: its rate of increase in 

 successive years is sensibly uniform. We believe that 

 this is the longest series of accurate determinations of 

 horizontal force made in one place. 



From all the comparative observations of horizontal 

 force, made by the methods of Article 25, which could 

 be collected about forty years ago, combined by the 

 aid of a theory to which allusion is made in Article 

 24, (to be fully explained in Articles 47 and 49), Gauss 

 formed a series of maps of lines of equal horizontal 



Fig. 28. 



