CELESTIAL MEASURINGS AND WEIGHINGS. I9I 



length of a degree of its circumference is 364,578 Eng- 

 lish feet ; or very nearly as many thousand feet as there 

 are days in a year. 



2d. Though Jieaf'ly, the degrees are not precisely 

 equal. In all geographical longitudes the degrees of lati- 

 tude are found to increase in length in going from the 

 equator towards the poles. An increase in the length of 

 a degree indicates a less amount of curvature. The 

 earth's surface is therefore less curved, or less convex 

 that is, flatter as we approach its poles on all sides 

 from the equator. Its form then is elliptical, or obiafe, 

 and its polar diameter somewhat shorter than its equato- 

 rial. From the most recent calculations (those of Cap- 

 tain Clarke, founded on a general assemblage of all the 

 measured arcs) it results that the difference of these two 

 diameters is one 292d part of the former. 



3d. That tlie length of its polar diameter is 41,707,796 

 British imperial standard feet, which is within a single 

 furlong of 500,500,000 such inches. 



(14.) Hence it follows, that if we were to increase all 

 our imperial standard measures, each by one precise thou- 

 sandth pai't* and designate the measures so increased Ijy 

 the epithet geometrical instead of i77iperial, a geometrical 

 inch would be the exact 500,000,000th part ; a rod ot 

 fifty such inches the exact io,ooo,oooth part of the 

 earth's polar axis; and one of twenty-five such (which 

 might be called a geometrical cubit) the io.ooo,oooth 



I have before me for ordinary use two foot rtiles, both i)oiiglit 

 at respectable shops, and not the worse for wear, -vhich differ \>y 

 more than this amount. 



