PHYSICAL PROPERTIES OF WATER, ETC. 29 



Hence the relative compressibilities of sea and fresh water are about 



0-925 ; 

 while the rate of diminution by increase of pressure is sensibly the same (3^ per cent, 

 per ton weight per square inch) for both. 



" With the same apparatus I examined alcohol, of sp. gr. 0'83 at 20° C. 



These experiments were not so satisfactory as those with water. There are peculiar 

 difficulties with the silver film. I therefore make no definite conclusion till I have an 

 opportunity of repeating them." 



It will be observed that the diminution of compressibility as the pressure is raised 

 is here brought out unequivocally for all the three liquids examined. 



In the course of another year I had managed to obtain similar results for a range 

 of temperature of about 9° C. They were described in Proc. Roy. Soc. Edin., vol. xii. 

 pp. 757, 758, 1884, as follows: — 



"I had hoped to be able, during the winter, to extend my observations to 

 temperatures near the freezing point, but the lowest temperature reached by the large 

 compression apparatus was 6° - 3 C. ; while the highest is (at present) about 15° C. 

 From so small a range nothing can be expected as to the temperature effect on the 

 compressibility of water, further than an approximation to its values through that 

 range. 



" The following table gives the mean values of the average compression per ton 

 weight per square inch : — 



\ 



3i 4 



660 



637 



"These are all fairly represented by the expression 



0-00743 - 0-000038 t - 0-00015 p, 



