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E. F. PIGOT. 



A PHOTOGRAPHIC FOUOAULT-PENDULUM. 

 By Rev. E. F. Pigot, s.j., b.a., m.b. 



[Read before the Royal Society of N. 8. Wales, December 6, 1916.'] 



The following notes have unavoidably been put together 

 somewhat hastily, but I thought nevertheless that a brief 

 account of some trial experiments with a new apparatus 

 might be of interest to the Society, even before more pre- 

 cise results were obtained. 



It was in the small hours of the morning of January 8th,. 

 1851, in Paris, that Leon Foucault obtained the first 

 successful result of his classical pendulum-experiment r 

 demonstrating the rotation of our planet on its axis. The 

 progressive apparent change in azimuth of the plane of 

 vibration of a long heavy pendulum had, without his know- 

 ledge, been observed two centuries before by Viviani, at 

 Florence; but the honour rests with Foucault of having 

 discovered, from theory, the physical law governing this 

 movement (as a close approximation at least), and of having 

 verified it by actual experiment. 



In order to thoroughly investigate the truth of his now 

 well-known " sine-law," his pendulum experiment was 

 repeated, especially in 1851 and 1852, in many countries of 

 the world, — in France (5 cities), England and Ireland (5) t 

 Holland (4), Germany (3), Switzerland (2), Italy, Denmark,. 

 Canada, United States, Ceylon, and Brazil (1 each), and in 

 many cases with extreme care. Of course I am not to be 

 understood as referring now to the experiment as doubtless 

 frequently performed merely for lecture-demonstration 

 purposes, but as carried out with the rigorous attention to 

 detail demanded by scientific research. In all these various 



