Mr. A. Claudet on Moving Photographic Figures. 271 



points to the inference that large waves act on a small sphere 

 in the manner of an attractive force by the accumulation of 

 pressure on the further side of the sphere, and that small waves 

 act in the manner of a repulsive force by reason of a defect of 

 pressure on that side. The abstract demonstration of these 

 effects of the vibrations of an elastic fluid, besides being inter- 

 esting as a matter of pure reasoning, appears to have an exten- 

 sive physical bearing, as suggesting that the sethereal medium 

 in which the waves of light are known to be generated and 

 transmitted, may be the source from which all attractions and 

 repulsions derive their energy. I consider that in this commu- 

 nication a more secure basis is laid for a hydrodynamical theory 

 of the physical forces than in any previous attempt that I have 

 made. The former researches are vitiated by the adoption of 

 the commonly received law, that the condensation in central 

 motion varies inversely as the distance, which I now consider to 

 be an error. This is more especially the case with respect to 

 the Theory of Gravity proposed in the Philosophical Magazine 

 for December 1859, for which the present researches supply a 

 substitute. 



Cambridge, September 11, 1865. 



XXXVI. On Moving Photographic Figures, illustrating some Phe- 

 nomena of Vision connected with the combination of the Stereo- 

 scope and the Phenakistoscope by means of Photography. By 

 A. Claudet, F.R.S.* 



FROM the beginning of photography it must have struck 

 many of those who were acquainted with the phenomenon 

 illustrated by the phenakistoscope invented by Plateau, that 

 photography could produce with advantage the series of pictures 

 used in that instrument, on account of their possessing a greater 

 degree of accuracy than when made by hand. At a later period, 

 when the stereoscope had become popular from its application to 

 photography, there must have been a still stronger incitement 

 to make use of that process to produce binocular pictures for the 

 phenakistoscope, in order to combine the stereoscopic effect with 

 the illusion of moving figures elicited in the phenakistoscope. 

 Por example, if a number of binocular photographic pictures 

 were taken of a machine in various consecutive stages of its 

 motion, these pictures, applied to a phenakistoscope, would give 

 a complete illusion of the machine in perfect relief and in its full 

 action. 



* Communicated by the Author, having been read, the 7th of Septem- 

 ber, 1865, before the British Association at Birmingham. 



