288 SEE— THE CAUSE OF EARTHQUAKES. [October 19, 



After a careful inquiry by many experienced physicists the concki- 

 sion was reached that the water had been forced slowly but bodily 

 through the thick walls of the glass under a pressure of less than 

 1,000 atmospheres, in an interval of less than an hour's time. 



In the year 1661 a well-known experiment was made by the 

 Florentine academicians who forced water through the solid walls 

 of a sealed hollow sphere of gold, and other metals, by changing the 

 shape of the sphere under mechanical applications of pressure, so 

 as to diminish the volume. The present case of the porosity of glass 

 was thus verified from the opposite point of view, by the steady 

 application of external fluid pressure, on the spherical surfaces of 

 glass balls sent down in modern soundings of the ocean depths. 



The great porosity of all matter has of course long been recog- 

 nized by physicists, but we are so accustomed to dealing with small 

 forces and the resulting doctrine of the impenetrability of matter 

 that it is doubtful whether our appreciation of this fact has yet 

 passed beyond the academic stage. In his well-known " Properties 

 of Matter," fourth edition, p. 87, Tait says : 



" The porosity of wood, necessary for the circulation of sap, is beauti- 

 fully shown by the fact that, from microscopic examination of a thin slice 

 of fossil tree, a botanist can tell at once the species to which it belonged. 

 The greater part of the material of the wood has disappeared for it may 

 be millions of years, but its microscopic structure has been preserved by the 

 infiltration of silicious or calcareous materials which, hardening in the pores, 

 have thus preserved a perfect copy of the original. The rapid passage of 

 gases through unglazed pottery, iron and (hot) steel, etc., shows the porosity 

 of these bodies in a very remarkable manner. So does the strange absorp- 

 tion of hydrogen by a mass of palladium. The porosity of steel has recently 

 been shown in a most remarkable manner by Amagat, who forced mercury 

 through a thickness of more than three inches under a presure of at least 

 four thousand atmospheres. The metal was quite impervious to glycerine 

 under the same pressure." 



At the time this passage was written, some twenty years ago, 

 Tait remarked that decisive proof of the porosity of vitreous bodies, 

 such as glass, had not yet been obtained, but added " that they 

 form almost a solitary class of exceptions to an otherwise general 

 rule seems highly improbable." He then proceeded to show that all 

 bodies whatsoever must necessarily be porous and leaky when sub- 

 jected to great fluid pressure, and he pointed out that the penetra- 

 bility depended greatly on the character of the fluid, thus indicating 

 the great influence of molecular and atomic forces. 



