182 On the Electrical Phcetiomena exhibited in Vacuo. 



I tried to make a vacuum above the fusible alloy of bismuth ; 

 but I found it so liable to oxidate and dirt the tube, that I soon 

 renounced further attempts of this kind. 



On a vacuum above fused tin I made a nmnber of experi- 

 ments ; and by using freshly cut pieces of grain tin, and fusing 

 them in a tube made void after being filled vv^ith hydrogen, 

 and by long continued heat and agitation, I had a column of 

 fused tin which appeared entirely free from gas: yet the va- 

 cuum made above this, exhibited the same phaenomena as the 

 mercurial vacuum. At temperatures below 0°, the light was 

 yellow, and of the palest phosphorescent kind, requiring almost 

 absolute darkness to be perceived ; and it was not perceptibly 

 increased by heat. 



I made two experiments on electrical and magnetic repul- 

 sions and attractions in the mercurial vacuum, by attaching to 

 the platinum wire two fine wires in one case of platinum, in 

 the other of steel, terminated by minute spherules of the same 

 metals; I found that they repelled each other when the wire 

 was electrified in the most perfect mercurial vacuum, as they 

 would have done in usual cases ; and the steel globules were 

 as obedient to the magnet as in the airj which last result it 

 was easy to anticipate. 



In some of the first of these experiments, I used a wire for 

 connecting the metal with the stop-cock ; but latterly, the rare- 

 fied air or gas was the only chain of communication : and this 

 circumstance enabled me to ascertain that the feebleness of the 

 light in the more perfect vacuum was not OAving merely to a 

 smaller quantity of electricity passing through it ; for the same 

 discharge whicli produced a faint green liglit in the upper part 

 of the tube, pi'oduced a bright purple light in the lower part, 

 and a strong spark in the atmosphere. 



The boiling point of pure olive oil is not much below that 

 of mercury ; and the butter or chloride of antimony (antimo- 

 nane) boils at about .^88^ lahrenheit. I tried both these sub- 

 stances in the vacuum, and found, as might be expected, that 

 the light produced by the electricity passing through the va- 

 pour of the clilor-de was much more brilliant than that pro- 

 duced by it in passing through the vapour of the oil ; and in 

 tlie last it was more brilliant than in the vapour of mercury at 

 common temperatures; the lights were of different colours, 

 being of a pure white in the vapour of tlie chloride, and of a 

 red, inclined to purple, in that of the oil ; and in both cases 

 permanent elastic fluid was produced by its transmission. 



The law of the diminution of the density of vapours by di- 

 minution of temperature, has not been accurately ascertained; 

 but I have no doubt, fi'om the experiments of Mr. Dalton, 



and 



