300 On the Thermal Conductivity of Water. [Jan. 6, 



VIII. "Additional Note to a Paper 'On the Thermal Conductivity 

 of Water.' ".* By J. T. Bottomley, Lecturer in Natural 

 Philosophy, and Demonstrator in Experimental Physics in 

 the University of Glasgow. Communicated by Professor 

 G. G. Stokes. Sec. U.S. Received December 21, 1880. 



(Abstract.) 



In the former paper, the author had supposed that by taking a 

 vessel of very large horizontal section he should be able to eliminate 

 the sensible effects of conduction of heat downwards by the sides 

 of the vessel. However, considering the important part which 

 the sides might conceivably play, and the statements in books and 

 published writings that the conduction of heat downwards in liquids in 

 the experiments of Despretz and others, was wholly, or almost wholly, 

 due to conduction by the sides of the containing vessel, it was thought 

 advisable to put the matter to a direct test. 



A screen of thick cotton material was accordingly placed inside the 

 cylindrical vessel used in the experiment. The screen extended all 

 round, at a little distance from the side, and reached from top to 

 bottom, and accordingly would arrest currents of convection arising 

 from beat conducted down the side, if such were sensible. 



Experiments made in March and April, 1880, gave for the con- 

 ductivity of heat by water, in square centims. per second, a mean of 

 0"00134 without the screen, and 0*00154 with the screen. These 

 numbers, though not in complete agreement, are yet quite of the same 

 order. They indicate that no important error is to be feared as the 

 result of conduction down the walls of the bath. Indeed, the apparent 

 conducting power of water comes out a little greater with the screen 

 than without. 



* For an abstract of the paper see " Proe. Eoy. Soc," vol. 28, p. 462. 



