542 Mr. R. Mallet on the Vorticose Movement, 



elegant statement of words ; and to render the matter quite 

 familiar, have prepared a model of one of the Calabrian pe- 

 destals, figured by Mr. Lyell, which will exhibit to the eye all 

 the phasnomena already adverted to, by giving by the hand 

 a rectilineal horizontal motion to the base*. 



I have now proved that no vorticose motion is requisite to 

 account for the twisting of obelisks, &c, as observed in earth- 

 quakes, and that nothing more than a simple horizontal rec- 

 tilineal motion is demanded ; but, it may be asked, if this rec- 

 tilineal horizontal motion in earthquakes be an alternate one 

 also — if the earth shake both back and forwards — how is it 

 that these and other displaced bodies are not moved back into 

 their places again by the reverse motion, by the same sort of 

 motion, acting in the contrary direction? 



This question is, I believe, fertile in consequences, and its 

 consideration has led me to some further conclusions as to the 

 nature of earthquake motions. The first reason obviously is, 

 that as the forward movement has by displacement produced 

 a new set of conditions as to the centres of gravity and of ad- 

 herence of the stone and base, so it can scarcely by possibility 

 ever occur that there shall be precisely such as to give rise to 

 such a new form of twisting motion as shall neutralize that 

 first produced, although it is quite probable that some second 

 twisting may be produced by the backward stroke or motion ; 

 for this view I am indebted to my friend Dr. Apjohn. But 

 this alone is not sufficient. After looking through a great 

 number of authors, on earthquakes, I have not been able to 

 find one that has endeavoured, far less succeeded, in shaping 

 to himself any distinct notion as to what the precise nature of 

 the earthquake movement is. The ancients, appealing to their 

 senses, so far as these could guide them, thought that it was 

 like the shaking of a sieve, as the word a-evafio 9 tells us. The 

 moderns in general are not more exact in their notions : a 

 trembling, a vibration, a concussion, a movement, and so forth, 

 are the words we find scattered through even scientific authors. 

 Mitchell, Lyell and Darwin, with some others, although they 

 obviously have formed no distinct idea on the subject, use the 

 word " undulation," and in so far, have come nearer to the 

 truth ; for it appears to me, that the fact, that displaced bodies 

 are not occasionally replaced, in earthquakes, is conclusive 

 evidence of either one of two things : either the motion is 

 limited to horizontal direct movement, in one or more direc- 

 tions ; and, if so, the whole mass of the disturbed country 

 must be pushed bodily forward, and remain so, of which there 



* Exhibited at the Geological Society of Dublin, from whose Transac- 

 tions this paper is extracted. — Read 8th December 1845. 



