C. GENERAL PHYSICS. 131 



ematiciaiis, seems to be treated by the author with clearness, 

 in that he expresses the law of the molecular resistance by 

 the summation of two integrals, each depending upon the fig- 

 ure of the body and the nature of their applied forces. In the 

 application to special cases of the very general formula which 

 lie deduces in the first portion of his essay, its convenience 

 at once becomes apparent by the readiness with which it re- 

 duces to very simple equations. Thus, by its means, the 

 problem to find the curve of a beam acted on by its own 

 weight, and by forces that bend it into a complete semicircle, 

 is resolved in less than a page of text, and by one simple sub- 

 stitution ; and the author points out how the general formula 

 given by him can be applied to any engineering problem in 

 the consideration of the strength of materials. Atti della R. 

 Ac. D. Scienze, Turin, 1873,VIIL, p. 33. 



A NEW METHOD FOE THE DETERMINATION OF ELASTICITY. 



Among the inaugural dissertations of the competitors for 

 the Degree of Philosophy at the University of Jena, we no- 

 tice one by Hulsse, detailing a new method of determining 

 the co-efficient of elasticity. The author states that this 

 method was suggested to him in connection with his labors 

 at Dresden, in 1871,-as an assistant to the Royal Commission 

 on standards of Wei oh ts and Measures. In connection with 

 the use of very accurate balances, he remarks that the rela- 

 tion between a loaded and an unloaded balance ought to 

 give the means of determining the co-efficient of elasticity of 

 the balance-beam, an idea that seems to have been previously 

 suggested by Ilartig in 1859; and the authors plan consists 

 in determining the deflection of the end of the beam from the 

 observed duration of the vibrations under different loads, and 

 also in determining, independently, by theoretical formula?, 

 the same time of vibration under the assumption that no de- 

 flection takes place. By the comparison of the two results 

 he arrives at the co-efficient of elasticity. The difficulties ex- 

 perienced by former investigators have. consisted mainly in 

 the fact that they have attempted to measure directly the 

 deflection of a beam, although the quantity itself is extremely 

 small. The author applies his method of vibrations to beams 

 made of three different kinds of wood, and deduces the co-ef- 

 ficients of elasticity from a number of series of experiments 



