be agreeable 

 to it.- 



Abbe Haiiy's 



1()8 ATTRACTION AND REPULSION, &C, 



be proportional to the horizontal breadth of the plane di- 

 Follows the vided by the square of this distance. The tendency of the 

 attraction^ ° two planes toward each other, therefore, will follow the ge- 

 neral law of attraction, that is to say, it will be in the in- 

 verse ratio of the square of the distance. 

 Put to the test Desirous of knowing- how far these results of my theory 

 ofexperimem ' were agreeable to nature, I requested Mr. Hauy to make 

 some experiments on this delicate and curious point in na- 

 and found to tural philosophy. He complied with my wishes, and found 

 the formula? in perfect unison with experience. He parti- 

 cularly ascertained the singular phenomenon of an attraction 

 changed to repulsion hy the increase of distance, as the fol- 

 lowing note I received from him will show. 



" I suspended a small square leaf of laminar talc to a very 

 experiments slender thread, in such a manner, that its lower part was 

 ontiesu jec . J mme j. ge( j j n W ater. In the same water, at the distance of a 

 few centimetres, I immersed the lower part of an ivory pa- 

 vallelopipedon, so that one of its faces was parallel to the 

 leaf of talc. I then caused the parallelopipedon to advance 

 very slowly toward the leaf of talc, keeping it still in a pa- 

 rallel position, and stopping at intervals, to be. certain 

 the' motion, that might be imparted to the fluid, did not 

 sensibly affect the experiment. The leaf of talc then re- 

 ceded from the parallelopipedon ;' and when, on continuing 

 to move the latter with extreme slowness, there remained but 

 a very small distance between the two bodies, the leaf of talc 

 suddenly approached the parallelopipedon, and came into 

 contact with it. I then separated the two bodies, and found 

 the parallelopipedon wetted to a certain height above the le- 

 vel of the water ; and on repeating the experiment, without 

 wiping it, the attraction began sooner ; sometimes indeed 

 it took place from the first, without being preceded by any 

 perceptible renulsion. These experiirients, carefully re- 

 peated several times, always afforded the same residts." 



[V 



