On the Vorticose Movement accompanying Earthquakes. 537 



intense. But if such be the received notion, what then is left 

 in the aether but force or centres of force?" To this I reply, 

 that almost infinitely has no meaning but finitely, and there- 

 fore that the supposed aether, under this description, is pre- 

 cisely in the same category as all other fluids. But I add, in 

 regard to the latter sentence, that the mathematical considera- 

 tions which I have detailed above, show that there is some- 

 thing in the aether besides force or centres of force, namely 

 inertia. And I repeat the expression of my own opinion, 

 that it is easier to conceive this as indicating substance (how- 

 ever obscure the idea may be), than to frame a system of laws 

 applying to centres of force which shall represent its effects 

 equally well. 



I am, Gentlemen, 

 Royal Observatory, Greenwich, Your obedient Servant, 



May 12, 1846. G. B. AlRY. 



LXXXII. Explanation of the Vorticose Movement, assumed 

 to accompany Earthquakes. By Robert Mallet, C.E., 

 M.R.I. A., Ph.D., fyc, Secretary of the Geological Society of 

 Dublin *. 



TN our progress to the ascertainment of physical knowledge, 

 *■ the removal of error is next in importance to the discovery 

 of that which is true, inasmuch as by the former the road is 

 cleared, by which the difficult journey towards truth is to be 

 accomplished. The substitution, therefore, of a true for a 

 false explication of phaenomena, however in themselves unim- 

 portant, is never to be neglected ; and with this view it was 

 that I some time since addressed myself to the discovery of 

 what I believe to be the true explanation of a somewhat sin- 

 gular and heretofore puzzling circumstance attendant upon 

 the effects of earthquakes upon buildings, which has been 

 frequently observed, and has been hitherto explained, so far 

 as it has been attempted to be explained at all, by the assump- 

 tion of a vorticose or gyratory movement having been in some 

 inexplicable way given to the ground. The phaenomenon 

 alluded to, is the displacement of the separate stones of pe- 

 destals or pinnacles, or of portions of masonry of buildings by 

 the motion of earthquakes, in such a manner that the part 

 moved presents evidence of having been twisted in its bed 

 round a vertical axis. 



The first notice I find recorded of such a peculiar motion, 

 is in the Philosophical Transactions, in an account of the 



* Communicated by the Author. 

 Phil. Mag. S. 3. No. 1 90. SuppL Vol. 28. 2 O 



