262 



Trans. Acad. Sci. of St. Louis. 



sions assumed are approximate only, and since the flexure 



/ W\ 2 

 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 rectangular 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 D has been computed for the load of 100 lbs. at the ends 

 for x — 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- 

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



