362 Preliminary Note on the 



and the apparent compressibility of water in glass at this 

 temperature (12-5 C.) in volumes per thousand per atmosphere, 

 is 



H_ 5-8782 



~P~ 129-5' 



= 0-04539. 



We see, then, that at pressures up to 240 atmospheres the 

 property peculiar to water of diminishing in compressibility 

 with rise of temperature is preserved unimpaired, and the 

 amount of change corresponds closely with that found at low 

 pressures in the experiments of Regnault and Grassi. 



In Table II the details of the experiments on the effects 

 of pressure on the glass rod are given. The length of the rod 

 from point to point was 75-05", at the temperature of the 

 laboratory, 13 C. Its diameter was 0-28", and was very 

 uniform. The weight of the rod was 209-5 grammes. The 

 substance of the rod was remarkably homogeneous, there 

 being a complete absence of air-threads. 



The micrometers used were, at the east end a photographic 

 copy of Hartnack's eye-piece micrometer, and at the west end 

 one of Merz's. They were both compared, and the value of 

 their divisions, as used, determined by comparison with a 

 stage micrometer of Smith & Beck, obligingly lent to me by 

 my friend Dr William Robertson, who had very carefully 

 verified its graduation. It was remarkable as a coincidence 

 that the values of the divisions turned out to be identical in 

 both, namely, 0-000417". 



Under A we have the manometric pressures, under B and 

 C the micrometric determinations of the expansion at the east 

 and the west end respectively, and under D the sum B and C, 

 or the total expansion of the rod. It will be seen that while 

 the values of D, or the total expansion, are very concordant in 

 each series, those of B and C individually are not always so, 

 the excess being sometimes at the one end and sometimes at 

 the other. The effect of the rise of pressure is to extend the 

 containing tube, and to compress the contained rod. On the 

 relief of pressure the tube shortens again, and the rod recovers 



