136 On the Coiitract'jon of IVuter ly Hrat. 



congealing, and wliile still fluid, is actually somewhat di- 

 lated previous to the remarkable expansion which accom- 

 panies its conversion into ice. 



Dr. Hooke, however, continued uns-haken, and retained 

 the doubts he had expressed. 



Kemaikable as the tact, as now stated, nnist have ap- 

 peared, it seems not to have excited particular attention, nor 

 to have solicited more minute examination; and, indeed, 

 though philosophers did not lose sight ot" it, vet for near a 

 century no one investigated it more carefully. iSlairan, in 

 his Treatise on Ice in 1749, aiid Du Crest in his Disserta- 

 tion on Thermometers in 1757, appear to be well aware ot 

 this property of water; but it is to M. de Luc that we owe 

 the knowledge of the leading and more interesting circunw 

 stances. (Vide Rrclierc/ics, &c. 1772.) 



Having devoted his attention to the examination and im- 

 provement of the thermometer, he was naturally led to the 

 investigation while engaged in ascertaining the pha2nomena 

 of the expansion and contraction of dilVerent Huids by heat 

 and cold. 



He employed in his experiments thermometer glasses ; 

 and the included water, at or near the term of liquefaction, 

 descended in the stem, and appeared to him to suffer a di- 

 minution of bulk by every increase of temperature till it 

 arrived at 1116 41". From this point its voknne increased 

 ■with its temperature, and it ascended in the lube. This 

 fluid, when heated and allowed to cool, seemed to him to 

 contract in the ordinary v^ay, till its temperature sunk to 

 the 41", but to expand and increase in volume as the tem- 

 perature fell to the freezing point. 



The density of water, he thence inferred, is at its maxi- 

 mum at 41*', and decreases with equal certainty wiielher 

 the temperature is elevated or depressed. 



M. de Luc says, indeed, that very nearly the same altera- 

 tion in volume is occasioned in water of temperature 41", 

 by a variation of anv given number of degrees of tempera- 

 ture, whether they be of increase or of diminution ; and 

 consequently, that the density of water at temperature 50'', 

 and at temperature 32°, is the same. 



This philosopher did pot conceive that the constitution 

 of water, in .elation to caloric, undergoes a change at the 

 temperature of 41°, such that short of this degree caloric 

 should occasion contraction, and beyond it expansion. He 

 imagined that heat in all temperatures tends to produce two, 

 but quite opposite, eff^ects on this fluid, the one expansion, 

 the other contraction. 



3 In 



