APPLIED MECHANICS — LECORNU. 283 



lation of the tension per square millimeter of cross section, a tension, 

 wliicli is proportional to L-. The inventor believes the device will 

 be of important service hi aviation. It hideed permits the regulation 

 of the tension of each wh-e of an aeroplane and further allows one to 

 see how to vary that tension m the tests made in the work shop. Such 

 tests would consist in overturnuig the aeroplane and scattering sand 

 uniformly over the wmgs sufficient in amount to ])roduce the equiv- 

 alent wiiid pressure m flight. Then by means of this tensiometer 

 each wire would be tested and the weak parts consequently found. 



The journal La Teclmique Moderne in 1910 opened an inquiiy mto 

 the fatigue of metals. The repUes received to the questions have not 

 always been concordant, but Charpy, after analyzbig and discussmg 

 them, believed he could state the folio whig conclusions: First, the 

 alteration in the metals remains negligeable until the deformation 

 passes a certaui lunit; second, the cause of the alteration is almost 

 always a local and progressive condensation and hardening. Con- 

 sequently it is important to so determme the dunensions of tlie piece 

 as to avoid permanent deformation at certain points; tliird, a close 

 examination of the form and appearance of each piece tells when it is 

 becoming bad. The quantity of metal must be determined with care 

 for all parts of the construction. It is necessary to avoid all altera- 

 tions at the moment of puttmg the apparatus into operation and to 

 be sure that each piece keeps its integral form so as to prevent any 

 necessaiy accidental antl haphazard repau's. The rigorous appUca- 

 tion of these rules wdll doubtless avoid those catas trophies which w^e 

 so much deplore. 



Along the same line, Boudouard sought to see whether the altera- 

 tion in metals could not be revealed by the study of the dampmg of 

 their vibratory movements. A sufliciently long vibratoiy move- 

 ment finally ruptures a piece of metal. Boudouard found that the 

 number of vibrations necessary for rupture varied mversely with the 

 carbon content of steel. Up to the present, however, he has not 

 succeeded in slioM'ing clearly the relation of the microscopic structure 

 to the damping. 



It has been known for a long while that a metal could be easily cut 

 with a cii^cular saw without teeth provided the disk had a sufliciently 

 rapid rate of rotation. This process has received a new application 

 in the Ryerson Laboratory at Chicago. A saw 1.32 meters in diam- 

 eter, turned by a dynamo of a 100 horsepower at 2,000 turns 2)er 

 minute, cut in two 610 millimeters of T iron. The saw, made of steel, 

 turn(Hl in an enveloj)e in the interior of which the saw was constantly 

 bathed with cokl water and the sheaf of si)arks was caught in a 

 trough of water at the side of the machine. The cut metal seemed to 

 undergo a real fusion due to the intensity of the heat developed from 

 the friction. The feeble heating of tlie saw is exj)lained by the fact 



