382 



Miscellaneous Intelligence, 



The surfaces he used were of glass ; each was attached to a disc 

 of cork, so as to render the whole of one mass or piece, of a spe- 

 cific gravity very little greater than that of the water in which 

 they were to be immersed, and the prisms formed in this way 

 were each accurately of the same size, weight, form, and surface ; 

 they were suspended by silk threads so as to form two pendulums, 

 the weight of each being in the water 1 gramme (15.44 gr.). The 

 thickness of each pendulum was 2 centimetres (.787 of inch), and 

 the surfaces of glass opposed to each other, 10 centimetres (3.9371 

 inches) long, and half that height. The length of the suspension 

 threads was 18 centimetres (7 1468 inches). It is not our object 

 here, however, to describe the apparatus, but simply to give a view 

 of the author's expectation, and generally of the results he ob- 

 tained. Operating with his apparatus, he found that when the sur- 

 faces were at any greater distance from each other at the commence- 

 ment of an oscillation than 2| millimetres (.09S4 of inch,) the time 

 required for the first half oscillation was the same, amounting to 7 

 seconds. Hence it followed, that at this distance the two liquid 

 layers on the moistened surfaces did not penetrate each other, and 

 that therefore the thickness of this layer must be less than { of a 

 millimetre (.0492 of inch). As, however, the object in view was 

 general confirmation rather than particular estimates of the 

 strength of action, this point was not pursued, and M. Girard 

 went aj once to distances so small as to be within the limit of 

 interference. These distances were five in number, measured by 

 the diameters of five different wires used ; the smallest being 

 ."563, the second .1127, the third .1579, the fourth .1917, and 

 the largest .2481 of a millimetre in diameter. Then the gravity 

 of the pendulums exerted in a direction opposite to their attrac- 

 tion, or in a horizontal line, was varied by moving the points of 

 suspension to different equal distances on both sides, from the 

 points at which the pendulums would have hung when just in 

 contact. The following is part of a table expressing the results. 

 Nos. 1, 2, 3, 4, and 5, are the wires, or the distances between the 

 surfaces at the commencement of the oscillation. The figures in 

 the first five columns express the gravitating power, in grammes, 

 opposed to the attraction, and tending to separate the surfaces ; 

 and the figures in the last five columns express the time, in se- 

 conds, required in the corresponding experiments to complete the 

 first half oscillation. 



