Compressibility of Glass 363 



its length, and there is necessarily a sliding of the one on the 

 other, and it depends entirely on minute local circumstances 

 whether the rod finds it easier to return to its original relative 

 position or to another. In some experiments made previously 

 to the date of those quoted in Table II, the rod had greater 

 freedom of motion longitudinally, and it happened several 

 times that it crept bodily to the one end, necessitating the 

 opening of the apparatus to replace it in a position suited to 

 observation. Afterwards stops were placed in the tube, which, 

 while setting limits to the crawling motion, did not in any way 



lere with the expansion and contraction. The results of 

 these previous experiments are not included in the table, 

 because they were merely tentative in order to learn the details 

 <>f the kind of experimentation; and further, because in the 

 mi< roscope at the east end the power used was very low, and 

 the micrometer insufficiently delicate. 



In the left hand columns the individual experimental data 



given. The arithmetical means of the manometric 

 pressures and of the total micrometric expansions are taken for 

 each series. These mean results are then further developed on 

 the right hand side of the table. First the temperature is 

 given, T. This remains always very constant, as it was the 

 temperature of the room, which varied very little. It was 

 further controlled between each experiment by the reading of 

 the manometer when the pressure was reduced to that of the 

 itmosphere. The pressure in atmospheres (P) is obtained. AS 

 < \ pi. lined above, by multiplying the manometric pressure (A) 

 by 3-13. 



P = 3*i3 x^. 



linear compression (F) for pressure (P) is given by multi- 



;i Tnmrtiir -\p. iii-inn by the value of a di\ 

 or 0-0004 1 7", 



F = 0'<xx>4i7* x D, 



in 



//= F. 



75-05 



// H the linear compn --i.n in m< h< - <>t .1 rod one million n. 

 long for pressure P. 



