HISTORY OE n CHRONOPHOTOGRAPHY. 337 



This last application of ehronophotography is sometimes somewhat 

 laborious. It is only mentioned to show the extreme power of the 

 method and the multiplicity of its applications. 



In closing it may be added that since the exhibition new applications 

 of ehronophotography have been made at the physiological station, 

 which promise the experimental solution of certain problems hitherto 

 looked upon as insoluble. 



: 



[Subsequent notes by I>r. Marey, translated from the Comptes Rendus of the Academy of Sciences, 

 Vol. CXXXII, p. 1291, meeting of June 3, 1901.] 



Since the communication which I had the honor to make to the 

 Academy on the 27th of May, 1900, I have seen that my apparatus 

 needed to be entirely reconstructed in a better form, but the resources 

 of my own laboratory did not permit it. 



Our correspondent, Mr. Langley, who is interested in these studies, 

 btained from the Smithsonian Institution, whose Secretary he is, a 

 ubsidy which has permitted me to resume my experiments, and to 

 present to the Academy these new results. I have also awaited the 

 result of the remarkable experiments of Professor Hele-Shaw, and it 

 has seemed to me desirable to bring together these two kinds of 

 research, which have a common purpose, that of fixing by means of 

 permanent images phenomena which escape direct observation. 



Besides this, since my last communication I have learned of the 

 labors of Mr. L. Mach, which are so closely related to my own that 

 I notice them in giving the history of the new methods which seem 

 destined to numerous applications. 



It was on the 11th of March, 1893, that I had the honor of present- 

 ing to the Academy m}^ first experiments, made by means of ehrono- 

 photography, on liquid waves or movements of the internal molecules 

 of these waves, and also of the changes of speed and direction in cur- 

 rents which meet bodies of diverse forms. After Mr. Mach's com- 

 munication of his experiments on the behavior of a current of air 

 under analogous circumstances, he developed this research in a later 

 communication on the use of an inhaling turbine, passing a steady 

 current of air into a quadrangular prismatic tube, whose section was 

 IS try 21 cm. The face of this tube, turned toward the observer, was 

 formed of transparent glass; the opposite face was blackened to form 

 a dark chamber, and an arc lamp projected its light into the interior 

 of the tube. 



Mr. Mach placed bodies of different forms and made of transparent 

 substances in the air current, and took different ways to render the 

 movements of the air in the vicinity of the bodies visible. Sometimes 

 he projected light bits of paper or silk in the air current sometimes 

 tine dust, sometimes smoke, and sometimes he hung flexible silk 

 sm 1901 22 



