20 6 Mr . 'Walker’s Experiments on the 
This was a day remarkably favourable for fuch an experi- 
ment* My thermometer expofed to the open air flood, at 
three quarters paft eight this morning, at + 6°, which is a very 
extraordinary degree of cold here ; but this experiment was 
not begun till noon. 
Exp. 5. On Jan. 14. I froze mercury at the Anatomy 
School again, in the prefence of the rev. the Dean of Chriffc 
Church, the rev. Dr. Hornsby, and Dr. Thomson. 
Four ounces now of the mixture of acids, prepared as in the 
firfl experiment, were cooled in a tumbler to — 20°, which 
required fomewhat more than an equal weight of fnow, cooled 
nearly to the fame temperature, to produce the greateft effect. 
This was fomewhat lefs than in the lafl experiment, the fpirit 
thermometer finking no lower than —46°, owing chiefly to the 
weather having become much warmer, the temperature of the 
open air being now 4-36°. The mercurial thermometer i ai- 
mer fed in this mixture funk to — 55 0 , where it became fla- 
tionary ; then two thermometer glafies, one half filled with 
mercury, and the other filled to a confiderable height up the 
the tube, after being immerfed fome time, were examined. 
Upon breaking the fhell of glafs from the former of thefe, the 
mercury was found in a perfectly folid flate ; but its upper 
furface, which was highly polifhed, and of the colour of 
liquid mercury, inflead of being only (lightly depreffed, as 
had been feen in every other inftance which afforded an oppor- 
tunity for infpedtion, now formed a perfe&ly inverted hollow 
cone. This great depreffion, as well as the concentric circles 
mentioned in a former inftance, I fuppofe, might be owing to 
a rotatory motion accidentally given to it whilfl congealing. 
The folid mercury was beaten out, but having been buffered 
to lie fome time on the table for infpe&ion, very quickly 
.6 , • melted 
