Contents xlix 



PAGE 



Appearance of brass tube after the experiment . 351 

 The conditions of the experiment with the copper 

 sphere were different and the destructive effect of the 

 collapse of the internal glass sphere was less serious 352 



Appearance of the copper sphere on returning from 

 a depth of 6000 metres ...... 353 



Discussion of the experiment in the tube . . 354 

 Discussion of the experiment in the sphere . . 355 

 Analogy with earthquakes ..... 356 



Resemblance to the case of a gun bursting when 

 fired with even the lightest plug of snow in the muzzle 357 

 Importance of time in physical considerations. 







25. PRELIMINARY NOTE ON THE COMPRESSIBILITY OF 

 GLASS. [From Trans. Roy. Soc. Edin. 1880, Vol. xxix. 

 P- 589] 358 



The instrument described in this paper with which 

 the absolute compressibility of glass was determined 

 was designed by myself and constructed by Messrs 

 Milne of Milton House, Edinburgh. It was an elabora- 

 tion of the principle of the instrument which I con- 

 : acted and used for the same purpose on board the 

 "Challenger," using a column of sea- water both as the 

 means and the measure of the pressure. 



Description of the instrument .... 358 



The substance of which the compressibility is sought 



must be in the form of rod or wire. 



It lies in a metal tube with glass ends through which 



the two extremities of the rod or wire can be observed 

 1 exactly fixed by micromet- 

 When ] ed in the envelope it reduces 



the length of the rod or wire by an amount which de- 

 Ms on its c.impn-^ibiht v. 



The displacements of the ends caused by the pres- 

 ;re are measured with the micrometer^ and the shoit 

 ol tin- rod is thus directly determined Th- 



sure brm- known tin- linear ( ompressibiht v "I the 

 .1 from it the cubical < ompr8M- 



bihtv. in the ordinary wav. both c oinpressibiht les being 



absolute 



: T 



is of glass rod the < imiprrssibilitv <>l \vhuli 



