34-2 CONTRACTION OF WATER BY HIAT. 



meters in 1757, appear to be well aware of this property 

 Modem experU of water, but it is to M. De Luc that we owe the knowledge 

 Luc!'° °^ the * eac * m g anc * more interefiing circumftances, (vide Re- 



cherches, &c. 1772.) 



Having devoted his attention to the examination and im- 

 provement of the thermometer, he was naturally led to the 

 inveftigation, while engaged in afcertaining the phenomena 

 of the expanfion and contraction of different fluids by heat 

 and cold. 

 He ufed ther- He employed in his experiments thermometer glafles ; and 

 aid^ound^he"' the incIll ded water, at or near the term of liquefaction, de- 

 water to defcend fcended in the flem, and appeared to him to fuffer a diminu- 

 ^"Ta^then tioR of bu 'k b > ever y increafe °f temperature, till it arrived 

 rife till freeing: at the 41ft degree. From this point its volume increafed 

 with its temperature, and it afcended in the tube. This fluid, 

 when heated and allowed to cool, feemed to him to contract 

 in the ordinary way, till its temperature funk to the 41°, but 

 to expand and increafe in volume, as the temperature fell to 

 the freezing point. 



Thedenfity of water, he thence inferred, is at its maximum 

 at 41°, and decreafes with equal certainty whether the tempera- 

 ture is elevated or deprefled. 

 fo that its den- M. de Luc fays, indeed, that very nearly the fame alteration 

 ^2® a° as ' n vo ^ ume ls occafioned in water of temperature 41 °, by a varia- 

 the fame. tion of any given number of degrees of temperature, whether 



they be of increafe or of diminution ; and confequently that 

 the denfity of water at temperature 50, and at temperature 

 32°, is the fame. 

 His theory. This philofopher did not conceive that the constitution of 



water, in relation to caloric, undergoes a change at the tem- 

 perature of 41°, fuch that (hort of this degree caloric mould 

 occafion contraction, and beyond it expanfion. He imagined 

 that heat in all temperatures tends to produce two but quite 

 oppofite effects on this fluid, the one expanfion, the other 

 contraction. 



In low temperatures, the contractive effects furpafs the 

 expanfive, and contraction is the confequence : In tempe- 

 ratures beyond 41°, the expanfive predominate, and the 

 -vifible expanfion is the excefs of the expanfive operation over 

 the contractive. 



In 



