JOHN WILLIAM DRAPER. 



were pursued in all the calamity of family bereavement, and in tin- 

 depths of forests, alike unused to music, to poetry, to philosophy." 

 His first experiments were addressed to the direct determination of 

 tin- attraction between mercury and glass, with the view of testing 

 Clairaut's mathematical deduction. After repeated trials he found 

 that a strong and uniform adhesion was obtained when the mercury 

 was pure and warm and the glass perfectly clean. Repeating the 

 experiment with an amalgamated disk of copper, of the same size, 

 the weight required for separation was regarded as measuring the 

 cohesion of the mercury itself. The results of a number of experi- 

 ments showed that in no ease did the attraction of mercury for 

 glass amount to half the cohesion of the mercury. But since a glass 

 plate on the surface of water is wetted, even after separation, it is 

 obvious that in this case the adhesion is greater than the whole co- 

 hesion ; hence the rise of water in a tube of glass is easily accounted 

 for. 



But an unexpected phenomenon was developed. On connecting 

 the mercury, dry and warm, to a gold leaf electroscope no disturb- 

 ance of the leaves took place so long as the glass plate was in con- 

 tact with its surface. But on separating them — and it required 

 considerable force to do this — both the mercury amd the glass be- 

 came strongly electrified, the mercury being negative and the glass 

 positive. Indeed, the development of electrification was so de- 

 cided as to tear asunder the leaves of the electroscope. Dr. Draper 

 naturally concluded that contact of mercury and glass developed 

 electrification ; that while in contact the electricity was " disguised " 

 and appeared only on separation ; and that since the two were op- 

 positely and strongly electrified, the force required to separate them 

 measured the electrical attraction. But this force measured also 

 the adhesion, by hypothesis; and hence adhesion must be an electri- 

 cal attraction. Two striking confirmations of this theory are given 

 in the memoir. In the first he repeated the mercury experiment 

 with disks of glass, gum-lac, sealing wax, sulphur, and beeswax, and 

 proved that the electrification, as measured with the torsion balance, 

 was for each disk proportional to the adhesion as measured by the 

 force required for separation ; and that for the several disks ex- 

 amined the values obtained diminished in the above order. In the 

 second he showed very ingeniously that electrification exercises an 

 apparent control over all the phenomena of capillary attraction. 

 One form of his apparatus consisted of an inverted siphon, the 



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