52 



A HISTORY OF 



long tube growing out of it. This being part- 

 ly filled with spirits of wine tinctured red, so 

 as to be seen when it rises, the ball is plunged 

 into boiling water, which making the spirit 

 within expand and rise in the tube, the water 

 marks the greatest height to which it ascends; 

 at this point the tube is to be broken off, and 

 then herrnetrically sealed, by melting the 

 glass with a blow-pipe; a scale being placed 

 by the side, completes the thermometer. Now 

 as the fluid expands or condenses with heat 

 or cold, it will rise and fall in the tube in pro- 

 portion; and the degree or quantity of ascent 

 or descent will be seen in the scale. 



No lire, as was said, can make water hotter, 

 after it begins to boil. We can, therefore, at 

 any time be sure of an equable certain heat ; 

 which is that of boiling water, which is in- 

 variably the same. The certainty of such a 

 heat is not less useful than the instrument that 

 measures it. It affords a standard, fixed de- 

 gree of heat over the whole world ; boiling 

 water being as hot in Greenland as upon the 

 coast of Guinea. One fire is more intense 

 than another; of heat there are various de- 

 grees; but boiling water is a heat every where 

 the same, and easily procurable. 



As heat thus expands water, so cold, when 

 it is violent enough to freeze the same, pro- 

 duces exactly the same effect, and expands it 

 likewise. Thus water is acted upon in the 

 same manner by two opposite qualities; being 

 dilated by both. As a proof that it is dilated 

 by cold, we have only to observe the ice 

 floating on the surface of a pond, which it 

 would not do were it not dilated, and grown 

 more bulky, by freezing, than the water which 

 remains unfroze. Mr. Boyle, however, put 

 the matter past a doubt, by a variety of ex- 

 periments." Having poured a proper quan- 

 tity of water into a strong earthen vessel, he 

 exposed it, uncovered, to the open air, in 

 frosty nights ; and observed, that continually 

 the ice reached higher than the water before 

 it was frozen. He filled also a tube with 

 water, and stopped both ends with wax: the 

 water, when frozen, was found to push out the 

 stopples from both ends ; and a rod of ice ap- 

 peared at each end of the tube, which showed 

 how much it was swollen by the cold within. 



Boyle, voL i. p. 610. 



From hence, therefore, we may be very 

 certain of the cold dilating of the water; and 

 experience also shows that the force of this 

 expansion has been found as great as any 

 which heat has been found to produce. The 

 touch-hole of a strong gun-barrel being stop- 

 ped, and a plug of iron forcibly driven into 

 the muzzle, after the barrel had been filled 

 with water, it was placed in a mixture of ice 

 and salt; the plug, though soldered to the 

 barrel, at first gave way, but being fixed in 

 more firmly, within a quarter of an hour the 

 gun-barrel burst with a loud noise, and blew 

 up the cover of the box wherein it lay. Such 

 is its force in an ordinary experiment. But 

 it has been known to burst cannons, filled 

 with water, and then left to freeze ; for the 

 cold congealing the water, and the ice swell- 

 ing, it became irresistible. The bursting of 

 rocks by frost, which is frequent in the north- 

 ern climates, and is sometimes seen in our 

 own, is an equal proof of the expansion of 

 congealed water. For having by some means 

 insinuated itself into the body of the rock, it 

 has remained there till the cold w as sufficient 

 to affect it by congelation. But when once 

 frozen, no obstacle is able to confine it from 

 dilating ; and, if it cannot otherwise find room, 

 the rock must burst asunder. 



This alteration in the bulk of water might 

 have served as a proof that it was capable of 

 being compressed into a narrower space than 

 it occupied before ; but, till of late, water was 

 held to be incompressible. The general opi- 

 nion was, that no art whatsoever could 

 squeeze it into a narrower compass ; that no 

 power on earth, for instance, could force a 

 pint of water into a vessel that held an hair's- 

 breadth less than a pint And this, said they, 

 appears from the famous Florentine experi- 

 ment ; where the water, rather than suffer a 

 compressure, was seen to ooze through the 

 pores of the solid metal ; and, at length, mak- 

 ing a cleft in the side, spun out with great 

 vehemence. But later trials have proved that 

 water is very compressible, and partakes of 

 that elasticity which every other body pos- 

 sesses in some degree. Indeed, had not man- 

 kind been dazzled by the brilliancy of one in- 

 conclusive experiment, there were numerous 

 reasons to convince them of its having the 

 same properties with other substances. Ice, 



