420 PHILOSOPHICAL TRANSACTIONS. [aNNO 1783. 



rose directly and became stationary ; the former at 40° or 40°^, the latter at 

 2Q%, both below the cypher. Having taken these out, he put in two others, 

 g and e ; the former became stationary at 40°, the latter at 30°. He then de- 

 canted the fluid quicksilver, to examine the internal surface of the frozen part, 

 which proved very uneven, with many radii going across ; some of these re- 

 sembled pins with heads. Urgent business called Mr. H. away an hour. On 

 his return he found a small portion only had liquified in his absence. He then 

 broke the phial entirely, and with a hammer repeatedly struck the quicksilver. 

 It beat out flat, yielded a deadish sound, and became fluid in less than a minute 

 afterwards. By the comparative observations of the several thermometers it 

 appears, that 30° on the scale of the spirit thermometers d and e, is about equal to 

 40° or 41° on the standard spirit thermometer h. The following was the state 

 of the instruments that morning, 



A. B. D. E. F. G. H. 



At 8" -103 - 80 33j 33 42| 42 .. ..46 



At 9 - 323 — 444 —29 — 29h 40 —40 . . -44 



At 12 34 32 21 2l£ 30 29i.. .. 34 



XX. Observations on Mr. Hutchins's Experiments for determining the Degree of 

 Cold at ivhich Quicksilver freezes. By H. Cavendish, Esq., F. R. S. p. 303. 



The design of the following paper is to explain some particulars in the appa- 

 ratus sent by Mr. C. to Mr. Hutchins, the intention of which does not readily 

 appear; and also to endeavour to show the cause of some phenomena which 

 occurred in his experiments ; and point out the consequences to be drawn 

 from them. 



This apparatus was intended to determine the precise degree of cold at which 

 quicksilver freezes : it consisted of a small mercurial thermometer, the bulb of 

 which reached about 1\ inches below the scale, and was inclosed in a glass 

 cylinder swelled at bottom into a ball, which, when used, was filled with quick- 

 silver, so that the bulb of the thermometer was entirely surrounded with it. If 

 this cylinder is immersed in a freezing mixture till great part of the quicksilver in 

 it is frozen, it is evident that the degree shown at that time by the inclosed ther- 

 mometer, is the precise point at which mercury freezes ; for as in this case the 

 ball of the thermometer must be surrounded for some time with quicksilver, part 

 of which is actually frozen, it seems impossible that the thermometer should be 

 sensibly above that point ; and while any of the quicksilver in the cylinder re- 

 mains fluid, it is impossible that it should sink sensibly below it. The ball of 

 the thermometer was kept constantly in the middle of the swelled part of the 

 cylinder, without danger of ever touching the sides, by means of some worsted 

 wound round the tube. This worsted also served to prevent the access of the 

 air to the quicksilver in the cylinder, which, if not prevented, would have made 



