368 



Preliminary Note on the 



is the same per atmosphere or the linear compressibility of 

 the glass. 



is the cubical compressibility of the same glass. 

 These results are summarised in Table III. 



TABLE III. Summary of Experiments made on the yd, 41/1, 

 and jth June 1880, on the Compression produced on a 

 Glass Rod by Pressures up to 240 Atmospheres. 



Two columns Q and 7? are added. Q gives the greatest 

 absolute deviation from the mean total expansion in any series, 

 R gives the deviation per cent. 



In the observations recorded I made no attempt to sub- 

 divide the micrometer divisions further than to estimate a 

 half. As the micrometer readings are not affected directly 

 by the pressure, the deviation per cent, should be, as it is, less 



