A'OL. XXV.] PHILOSOPHICAL TRANSACTIONS. 30Q 



(which I mention, because the humidity in the air would sometimes render the 

 experiment unsuccessful even in glass, or at least greatly impair the appearance) 

 which had an influence on the varnish, somewhat to soften it. However, the 

 success of the experiment was, that when the gallipot, with its contained mer- 

 cury, came to be in vacuo, on shaking the pump a light appeared, and that 

 without the concurrence of glass, or the favour of a more proper season to 

 assist it. I am also informed by several persons of credit, that the medicine 

 called mercurius dulcis, when broken in the dark, gives remarkable flashes of 

 light; which perhaps may be owing to the salts, with which each little globule 

 of the medicine is enveloped ; since I have often observed that loaf-sugar, when 

 struck or broke in the dark, affbrds a light; and I cannot tell, but that salts as 

 closely united in their parts as the sugar, may give a light on a violent separa- 

 tion of them, till I have made some trials; whether the medicine when broken 

 in vacuo, will affbrd any light. 2. What the salts will do without quicksilver, 

 both in the open air and in vacuo; for there are some bodies that appear light 

 in the dark in the open air, which altogether lose that shining quality in 

 vacuo. 



After the attrition of the exhausted globe was continued for some time, the 

 cock was turned, which permitted the air to insinuate into the globe, through 

 the joints of the screws; the motion of the great wheel, and the application of 

 the hands continuing all the while: and as the air filled the globe, so the ap- 

 pearance of the light continued to alter, till the like quantity of air had re- 

 entered, as was taken from it; then there appeared as great a difi^erence of light 

 from what was produced when evacuated of air, as when the experiment was 

 made with quicksilver in vacuo and in the open air. Certain specks of light were 

 then seen on the fingers that touched the globe, but without any great lustre; 

 and it was very remarkable, that while my hand continued on the glass, in mo- 

 tion, if any person approached his fingers towards any part of the glass in the 

 same horizontal plane with my hand, within an inch or thereabouts, a light 

 would appear to stick to the fingers, notwithstanding they did not touch the 

 glass; and my neckcloth at the same time, at an inch or 2 distant from it, ap- 

 peared of the colour of fire, without any communication of light from the 

 globe. The former part of both trials was alike, save only, that upon applica- 

 tion of white sheep's leather in the latter, a very good light was produced, 

 while the wool side was held next to the globe; but when the other side of the 

 same piece of leather was turned to the globe, no light ensued, though con- 

 tinued for some time; but as soon as it was changed again, the light would ap- 

 pear as at first, and so on several repetitions the same. 



As to the latter part of this trial, the air was not let in all at once, as before, 



