PHYSICAL PROPERTIES OF WATER, ETC. 



25 



in great part by a jacket containing water and pounded ice. We had no means of 

 ascertaining the average temperature of the glass rod, but it cannot have been more 

 than some 5 or 6 degrees above 0° C. This was done merely to ascertain whether glass 

 becomes less compressible or no as the temperature is lowered, not the amount of 

 change. The question appears to be answered in the affirmative. 



Early in the present year Mr. Buchanan kindly lent me his own apparatus, which 

 is in three respects superior to mine. (1) A longer glass rod can be operated on. 

 (2) The air can be entirely got rid of from the interior, so that when the glass tubes 

 give way there is no explosion. (3) The glass tubes are considerably narrower in bore 

 (though with equal proportionate thickness), and consequently stronger. I used my 

 own pump and external gauge, but the necessary coupling pieces were easily procured ; 

 and the reading-microscopes were fastened to a longer block of seasoned wood than 

 before. These experiments have been made near one temperature only, but it is about 

 the middle of the range of temperatures in my experiments on water and sea-water. 



It is not necessary' to print the details of the experiments in full. I give below part 

 of a page of the laboratory book for a single day's work, to show how far the experiments 

 of one group agree with one another. I purposely choose one in which the glass rod 

 was somewhat displaced in the apparatus during the course of the measurements : — 



23/2/88. 



Kew Standard, 9°-l C. 

 (Length of glass rod, 7575 inches.) 



Mean, 



0-0102 



(PHYS. CHEM. CHALL. EXP. — PART IV. 1888). 



