114 Mr. G. F. Rodwell on some Effects 



as gravity continues to predominate, rupture becomes more and 

 more imminent. When this occurs, the lower mass, no longer 

 restrained by the cohesion of the upper mass, and being now in 

 a medium of less than its own density, sinks to the bottom ; 

 while the upper mass, having suffered a slight decrease of den- 

 sity by being dragged into a warmer layer by the lower mass, 

 and being now liberated from that weight, is in a medium of 

 greater density than its own, and consequently ascends to the 

 surface. 



It is obvious that the portion of this explanation which relates 

 to the separation of the lower oil-mass applies equally to the 

 experiment first described, in which the oil-mass, instead of 

 floating in the medium, had its upper (plane) surface in contact 

 with the liquid surface. I may remark, in conclusion, that while 

 the former experiment takes about four minutes (from the com- 

 mencement of heating), the experiment last described does not 

 require more than one or two minutes. The latter experiment 

 is most effective, and best suited for the lecture-table. 



14 Denbigh Place, S.W. 

 January 11, 1867. 



Addendum. 



The following experiments (which were not finished in time 

 for insertion in the body of the text) would seem to prove the 

 correctness of the explanation given above as to the cause of the 

 lengthening of the oil-sphere into an ellipsoid, and its subsequent 

 resolution into detached masses, under the conditions of the de- 

 scribed experiment. 



In order to ascertain the comparative rate at which the liquids 

 employed in that experiment acquire a uniform temperature, a 

 litre of each was heated for an hour, under precisely the same 

 conditions, and the temperatures were observed at intervals of 

 ten minutes. The beaker containing the liquid was placed upon 

 a surface of sand (so that all parts of the bottom of the beaker 

 might be uniformly heated) spread in a thin layer upon a copper 

 plate heated by hot water. The temperatures were taken by 

 means of two thermometers reading accurately together, one 

 placed with the* lower part of its bulb 3 millims. from the bottom 

 of the beaker, and the other with the upper part of its bulb 3 

 millims. from the water- surface. The depth of the liquid column 

 was 130 millims. 



Distilled w r ater and methylated alcohol were first tried sepa- 

 rately. The temperature of the water was 6° C, and of the 

 alcohol 6°'5 C, the specific gravity of the latter at that tempe- 

 rature being 0*830. The following results were obtained : — 



