Of WATER by HEAT'. 381 



The fir ft obfervation relative to this fubject: was made by Dr 

 Croune, towards the clofe of the 17th century, while engaged 

 in inveftigating the phenomena of the great and forcible, though 

 familiar, expanfion which happens to water at the inllant of 

 freezing ; a matter which occupied, in a confiderable degree, the 

 attention of his fellow- members of the Royal Society of London 

 in the earlier years of that inflitution. 



I shall relate in his own words his firft obfervation : " I filled 

 " a ftrong bolt-head about half-way up the ftem with water, a day 

 u or two before the great froft went off, marking the place where 

 " the water ftood; and placing it in the fnow on my leads, 

 " while I went to put fome fait to the fnow, I found it above 

 " the mark fo foon, that I thought the mark had flipt down, 

 " which I prefently raifed to the water, and as foon as ever I 

 " mixed the fait with the fnow, the water rofe very fail;, about 

 " one-half inch above it. I took up then the glafs, and found 

 " the water all fluid ftill : it was again fet down in the fait and 

 " fnow ; but when I came about an hour after to view it, the 

 " ball was broke, and the water turned to hard ice, both in the 

 « ball and ftem*." 



From this experiment Dr Croune drew the conclusion, that 

 water, when fubjected to cold, actually began to expand before 

 it began to freeze. On announcing it, however, to the Royal So- 

 ciety, on the 6th of February 1683, Dr Hooke immediately ex- 

 preffed ftrong doubts, and afcribed the afcent of the water in 

 the neck of the vefTel to the fhrinking of the glafs occasioned 

 by the cold. 



To obviate this objection, and to preclude, as far as was pof- 

 fible, the influence of the change of capacity in the apparatus 

 from an alteration of its temperature, a bolt-head was immerfed 

 in a mixture of fait and fnow, and into it, when cooled, was 

 poured, to a certain height, water previoufly brought to near the 



freezing 



* Birch's Hijlory of the Royal Society, vol, iv. p. 263. 



