produced by a Fluid in Motion. 



117 



Time of taking the 



temperature from 



the commencement 



' of heating. 



Alcohol-and-water 

 mixture. 



Alcohol-and-water 

 mixture with 

 added alcohol. 



Mean temperature. 



Mean temperature. 



minutes. 

 10 

 20 

 30 

 40 

 50 

 60 



15 ? 375 C. 



20-875 



26125 



30500 



34125 



36-375 



14-375 C. 



19-375 



26000 



30500 



34 625 



37750 



On continuing to heat the mixture containing the added 

 alcohol, the upper layer in which it was present suddenly 

 coalesced with the liquid beneath it, and the entire mass of 

 liquid became at once of a uniform temperature. The lower 

 thermometer stood at 42° C, and the upper one at 36° C, im- 

 mediately before the coalescence. 



It is seen from the above experiments that the addition of a 

 small quantity of alcohol to a mixture of alcohol and water deter- 

 termines a very unequal acquirement of heat throughout the 

 mass of that mixture during the process of slow heating from 

 beneath. For, on account of the tardiness with which the added 

 liquid mixes with the liquid to which it is added, the mass be- 

 comes divided into two distinct layers, the upper one containing 

 more alcohol than the lower; and this latter receives almost all 

 the heat communicated to the liquid, until, when a certain tem- 

 perature has been attained, the two layers coalesce, uniformity of 

 mixture and uniformity of temperature being simultaneously 

 established throughout the mass. 



We have, I conceive, in the above results the explanation of 

 the cause of the change of the oil-sphere into an ellipsoid, and 

 its subsequent transformations ; for (as mentioned in the text) it 

 is a necessary condition of this experiment that the fluid medium 

 shall not during heating rapidly acquire a uniform temperature. 



14 Denbigh Place, S.W., 

 January 23, 1867. 



