230 
Proceedings of the Royal Society 
at dilferent temperatures. Grassi’s results were all obtained for 
pressures of some 10 atmospheres or so at the utmost; and, if they 
may be trusted, indicate a most extraordinary relation between the 
compressibility and the temperature of water within a few degrees 
of 4° C. It seems almost hopeless to attempt to obtain an approxi- 
djC 
mate value of at 4° C. from Grassi’s table. Yet this has been 
dp 
attempted by both of the authors above named. 
Puschl calculates that 87*6 atmospheres lower the maximum 
density point by V C. Thus he (virtually) gives the effect of 1 ton. 
per square inch as 1°‘7 C. instead of 2°-7 C. as above. Van der 
Waals gives a much more rapid descent, i.e., from 4° *08 C. at 1 
atmosphere to 3° *4 C. at 10*5 atmospheres. He also gives the 
results of some experiments with the ordinary piezometer, and 
therefore at very moderate pressures, which indicate a lowering of 
the maximum density point, but do not lead to definite numerical 
results. 
In order to clear up the whole subject, I intend to repeat all 
these experiments next winter, when the gun and its contents are 
naturally at a temperature of about 4° C. 
4. On Surface Emissivity. By Professor Tail. 
BUSINESS. 
Professor Tait laid before the Society a photograph of the arm of 
a child struck by lightning, sent by direction of Mr Milne Home. 
. Dr J. Graham was balloted for and declared a duly elected 
Bellow of the Society. 
Monday, lUh Jidy 1883. 
The Right Hon. LORD MONCREIFF, President, 
in the Chair. 
The Chairman read a Communication from the Science and Art 
Department ; and an Obituary Notice of the late Mr T. W. Rumble. 
The following Communications were read 
