. . ON HEAT AND LIGHT. 16$ 



that my conje&ures were well founded. The mercury in the 



three thermometers immediately began todefcend, and did not 



Hop till it had fallen very confiderably. 



The thermometer B fell from 162? to 152° ; C from 132^° Quantities of 



depremon. 

 to 1 1 J.| p ; and D from 106|° to 7Sf°. 



On comparing thefe numbers we find, that, in confequence 

 of the agitation of the cold water for two and twenty minutes, 

 the thermometer B fell 10° of Fahrenheit's fcale, the thermo- 

 meter C 23*,: and the thermometer D 28°. 



As foon as I had ceafed to ftir the cold water, the three 

 thermometers began to rife, and at the end of a quarter of an 

 hour they had all reached the points from which they let oat 

 at the beginning'-of this operation. 



To facilitate the companion of the refults of thefe two ex- Diagram to re* 

 periments, one made with cold water at reft, the other with ^ds?^ 

 the fame water in a (late of conftant agitation, I have repre- 

 fented them in Fig. 4. 



In the firft place we (hall learn feveral very interefting facls Obfervatlons 

 by iiraple infpe&ion of this figure ; we fhall fee, 1ft. that the j^^ 18 ^zi 

 progrefs of refrigeration, or, to fpeak more properly, the de- 

 creafe of temperature, was every where much more rapid, when 

 the cold water in contact with the extremity of the cylinder E 

 was agitated when it was at reft. 



2dly. That the extremity of the cylinder in contact with 

 this water was conftantly near 30° colder in the firft cafe than 

 in the fecond. 



• 3dly. We fhall fee, that the progrefs of refrigeration was 

 every where, and in both the experiments, fuch nearly as our 

 theory points out. 



The decreafe of temperature toward the middle of the cy- 

 linder was fo regular, that it is more than probable the appa- 

 rent irregularities toward the two extremities were occafioned 

 folely by the difficulty which a body of water finds in commu- 

 nicating its mean temperature to a folid, with which it is in 

 contact. 



The boiling water being in continual motion owing to its Agitation In- 



ebullition, it had a great advantage over the cold water, which creafed tiie •*• 



B . . ? ; ' fed* of the boil- 



was at reit, in communicating its temperature to the extre- ; ng water j^ 



mity of the cylinder it touched; but I have found, notwith- wife. 



Handing this, that by agitating the boiling water ftrongly with 



a quill, and particularly when with the quill I made a rapid 



M 2 friaion 



