262 



Trans. Acad. Sci. of St. Louis. 



sions assumed are approximate only, and since the flexure 



varies as I -^^1 it is possible that more exact data would 



give a result considerably different from the above. 



I have also taken the case of a solid rectano;ular brass 

 prism 6 feet long and 2 inches square supported at and turn- 

 ing about its center on a horizontal axis like a telescope tube, 

 two faces of the prism being in vertical planes. The deflec- 

 tions and astronomical flexures have been computed for every 

 ten degrees of zenith distance (1) with a load of 100 lbs. at 

 the end and (2) with an uniformly distributed load of 100 lbs. 

 on each half of the prism. The displacement of the neutral 

 axis J) has been computed for the load of 100 lbs. at the ends 

 for cc = 18 inches. The results are arranged in the following 

 table: — 



The experience of investigators of the elasticity and resist- 

 ance of materials has shown that formulae deduced from 

 theory do not give results which agree accurately with the re- 

 sults of experiments.* That the action of materials subject 

 to strains is more or less capricious has been abundantly 



* Weisbach says, " Except as exhibiting approximately the laws of phe- 

 uomena, the theory of the strength of materials has many practical defects." 



