1877.] On Attraction and Repulsion of Bubbles by Heat. 137 



kinds : — first, the annelid growth has determined outgrowth of the coral 

 which has covered in the worm-tube ; and second, the establishment of 

 some Hydrozoa on the ectoderm of the coral has sometimes produced the 

 formation of tubes of coral-structure which environ the stalk of the 

 offender and form a useful support to it. 



Finally it may be remarked that all the Madreporaria which were 

 brought up with the cable from off this area have an unusual orna- 

 mentation. 



I have to thank Sir James Anderson for the specimens and for the 

 details of the recovery of the cable. 



III. " On Attraction and Repulsion of -Bubbles by Heat."" By 

 Walter Noel Hartley, F.R.S.E., F.C.S., King's College, 

 London. Communicated by Professor Stokes, Sec. U.S. 

 Received February 26, 1877. 



In my first paper " On the presence of Liquid Carbon Dioxide in Mine- 

 ral Cavities " (' Journal of the Chemical Society,' February 1876), I 

 mentioned having noticed a remarkable repulsion of the bubbles in fluid- 

 cavities when they were approached by a heated body. I at first regarded 

 these movements as similar to those observed by Mr. Sang and Dr. 

 Hunter (Proceedings of the Royal Society of Edinburgh, 1872-73, p. 126) 

 in cavities of Iceland spar ; but with reference to the position of the 

 source of heat, I have since found that they occurred in quite the reverse 

 direction. The motion noticed by Mr. Sang was a repulsion of the 

 liquid ; that which I recorded was a repulsion of the gas by the heated 

 body. 



Here I may as well say that this refers to the real and not the appa- 

 rent direction of the motion as seen under the microscope. 



Professors Tait and Swan have shown (Proc. Roy. Soc. of Edinburgh, 

 1873-74, p. 2-17) that the attraction of the bubble by a heated body is a 

 natural effect if the liquid be of great volatility, in contact only with its 

 own vapour, as would be the case if the cavity were filled with carbonic 

 acid. Distillation of the liquid would take place when one side of the 

 bubble was heated ever so slightly above the temperature of the other, 

 and condensation would occur on the cooler side. This would occasion a 

 movement of the bubble from the cold to the warm side of the cavity ; 

 but it is not the Original bubble being simply propelled. Professor Tait 

 assumes that the liquid in Mr. Sang's specimens is carbonic acid, and 

 applies this explanation. This might well be the case, because the 

 attracting pieces of metal used were but a very few degrees warmer than 

 the specimens acted on ; but from other circumstances, some of which I 

 propose giving in detail, I am of opinion that these were water-bubbles. 



The attraction of a gas -bubble in a cavity containing liquid carbonic 



