180 On the Electrical Phanomena exhibited in Vacuo. 



The apparatus that I employed was extremely simple, (see 

 the figure,) and consisted of a curved 

 glass tube with one leg closed and 

 longer than the other, in this closed 

 leg a wire of platinum was hermeti- 

 cally cemented, for the purpose of 

 transmitting the electricity: or to as- 

 certain the power of the vacuum to 

 receive a charge, it was coated with 

 foil of tin oi platinum. The o})en 

 end, when the closed leg had been 

 filled with mercury or any other 

 metal, was exhausted either by being 

 placed under the receiver, or connected with the stop-cock of 

 an excellent air-pump ; and in some cases, to ensure greater 

 accuracy, the exhaustion was made after the tube and appa- 

 ratus had been filled with hydrogene*. 



Operating in this way, it was easy to procure a vacuum 

 either of a large or small size ; for the rarefied air or gas could 

 be made to balance a column of fluid metal of any length, from 

 20 inches to the 20th of an inch, and by using only a small 

 quantity of metal, it could be more easily purged of air. 



I shall first mention the results I obtained with quicksilver. 

 I found that by using recently distilled quicksilver in the tubes, 

 and boilnig it in vacuo six or seven times fi'om the top to the 

 bottom, and from the bottom to the top, making it vibrate re- 

 peatedly by striking it with a small piece of wood, a column 

 was obtained in the tube free from the smallest particle of air ; 

 but a phsenomenon occurred, in discovering the cause of which 

 I had a great deal of trouble. When I used a sliort tube of 

 four or five inches long only, I found, that after continued 

 boiling and much agitation of the mercury, though there was 

 no appearance of eia-tic matter, when the mercury adhered 

 strongly in the upper part of the tube, yet that, after electriza- 

 tion, or even on suffering the mercury to pass slowly back into 

 the closed part, a minute globular space sometimes appeared : 

 I thought at first that this was air, which, though so highly 

 rarefied as it must have been by the exhaustion, adhered to 

 the mercury ; and I endeavoured by long boiling the mercury 

 in an exhausted double syphon, and making the vacimm in 

 one of the curves, to prevent entirely the presence of air : but 

 the phaenomenon always occurred when there was no strong 

 adhesion of the mercury to the glass. This, and another cir- 

 cumstance, namely, that when the leg in which the torricellian 

 vacuum was made was 1 5 or 16 inches long, the phaenomenon 



* The figure will best explain the form of the npparatiis. 



was 



