Q30 MAXIMUM DENSITY OF WATER, 



repeated ; the cavity of the cork cup, (and which ftill remained there, af 

 cd"to £?! " ' ^*^ evident from the indication of the thermometer belong- 

 ing to the cup,) I placed feveral fmall cakes of ice in the 

 cylindrical veliel, which ice floating on the furface of the 

 water in the vefl*el, prevented that water from receiving heat 

 from the air of the atmofphere, which at that time was at the 

 temperature of 76° F. And as the cork cup had been a little 

 heated by the warm water in the foregoing experiment, time 

 wa>^ now given it to cool. 



As foon as the cup, and the whole mafs of the water in the 

 cylindrical vefTel appeared to have acquired the temperature 

 of freezing, I carefully removed the cakes of ice which 

 floated on the furface of the water, and introduced once more 

 the projeding conical point belonging to the metallic ball into 

 the ice-cold water in the veflel, placing it exa6lly in the 

 fame place which it had occupied in the foregoing experi- 

 ment ; but this ball, inflead of being at the temperature of 

 42** F. as before, was now at the temperature of 60® F. 

 The effefl was The refult of this experiment was very ftriking, and if I 

 niore confider- ^^ ^^* much raiflaken, affords a dire6t, unexceptionable, 

 able. and demonftfative proof, not only that the maximum of the 



denfity of water is in fa6t at a temperature which is feveral 

 degrees above the point of freezing; but alfo, that warm 

 currents do aftually fet downwards in ice-cold water, whenever 

 a certain fmall degree of heat is applied to the particles of that 

 fluid which are at its furface. 

 particul^s, The conical metallic point had been in its place no more 



than ten feconds when I diftin6lly faw that the mercury in the 

 thermometer belonging to the cork cup was in motion ; and, 

 when 50 feconds had elapfed, it has rifen four degrees, viz. 

 from SS*' to 36°. 



When two minutes and a half had elapfed, (reckoning 

 from the moment when the metallic point was introduced into 

 the cold water,) the thermometer had rifen to 39®, and at the 

 end of iix minutes to 39^'^, when it began to fall; but very 

 ilowly however, for at the end of eight minutes and a half it 

 was at 39|*='. 

 A thermometer A fmall mercurial thermometer, the bulb of which was 

 near the nutfide .^^^^ ^^ ^^^ ^^^^ ^^ ^j^^ ^^^^ ^^ ^^^ diftance of about 



or the cup was • * ' 



not affeaed. ,*^ of an inch from it, fhewed no figns of being in the leaft 

 affected by the heat communicated to the ice-cold water by 

 the metallic ball. 



This 





