278 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



has SO required. But experience shows that this palliative is not 

 sufficient. Fremont showed, by direct experunents, that it is well 

 to use buffer springs strong enough, by their compression, to reduce 

 the active force of the shocks whatever may be their intensity. It 

 seems that this necessity has not always been sufficiently taken into 

 account. 



Fremont has further been occupied concerning the ruptures which 

 frequently occur at the end of a certain period in the bent crank 

 shafts of locomotives, often putting such shafts out of service and 

 even causing serious accidents. He saw that such flaws result 

 especially from shocks received perpendicular to their motion, and 

 proposed, consequently, to increase the elasticity of such shafts by 

 hollowing out certain portions (the plates connecting the bodies of 

 the shafts with the bearings of the rods). Such a modification was 

 introduced into the eastern section of France, with so far very 

 encouraging results. 



IV. AERODYNAMICS. 



The progress of aerod3niamics has been intimately associated with 

 that of the perfecting of the motors as well as with the increase of 

 knowledge as to the action of air upon surfaces in movement. 

 I have already spoken of the motors. As to the dynamics of the aii*, 

 considered with regard to aviation, we may distinguish between the 

 theoretical and experimental results. Among the former there is 

 the important study of Soreau on the propellor, of which he spoke at 

 a conference last year of the Societe des Ingenieurs civils. Soreau 

 remarked that there are two schools devoted to the theory of the 

 screw. One considers the elements of the screw itself, without taking 

 into account the movements of the fluid molecules; the other school, 

 better comprehending the flow of liquids, finally reached an avowal 

 of their powerlessness and became strengthened in that avowal us the 

 study of the i)hysical phenomena showed increasing comi)lexity. 

 Soreau says that, after having sided with the latter school at first, 

 he now believes that it is possible to analyze the action of the blades 

 of the screw, with the double reservation that the action takes place 

 in a lunited space and that we be content with a})proxunate laws. 

 These laws lead to formulae no longer wholly cmphical, because, as 

 thus developed, they show the parts played by the various dunen- 

 sions, indicating their order of magnitude and relative influence. 

 Starting thence, the author has commenced to analyze, guided by 

 preconceived ideas, the better experiments on the subject and hopes 

 to get some general results. For some time analogous ideas have 

 guided the naval engineer Doyere in the study of marine screws, for 

 which investigations the Academic des Sciences, in 1911, bestowed a 

 part of the Yaillant prize. 



