42 On the Constitution and Construction of the 



as the mercury ascends in the thermometrical tube. Fourthly, 

 limited and local deposits of fused matter best account for 

 limited and local movements — for certain portions of the earth's 

 surface being repeatedly ruptured or disturbed, while others 

 appear to be in a state of complete repose. 



While it was supposed that the source of subterranean ac- 

 tion was at a vast depth under the surface, it was natural to 

 infer that the effects of one movement might extend over a 

 vast space. In common with many others, I was accustomed 

 to consider it as probable that earthquake shocks which syn- 

 chronised within a few hours, though happening in distant 

 countries, might proceed from one and the same effort of the 

 plutonic force. This was merely a conjecture, favoured by 

 some facts, and opposed by others. A dditional light has lately 

 been thrown on the subject by the researches of Mr David 

 Milne. The register of the shocks at Comrie for some years 

 past which he has published, and the record which he has col- 

 lected of those occurring abroad, shew that the synchronism 

 of shocks at distant localities, when carefully examined, wants 

 the accuracy and consistency necessary to prove a common 

 origin. Two well-known foci of disturbance are St Jean de 

 Maurienne in Savoy, and Comrie in Scotland, separated by 

 an interval of 1100 miles. It happens sometimes that an 

 earthquake occurs at both on the same day, and the coinci- 

 dence is thought remarkable. But on comparing a register of 

 the shocks at each for the five months from October 1839 to 

 March 1840, Mr Milne found that while no less than 150 were 

 observed at Comrie, and 58 at St Jean de Maurienne, there 

 was a complete want of that general agreement which a com- 

 mon origin would have produced.* Indeed, when we are ap- 

 prised of the frequency of the shocks at each locality, we na- 

 turally infer that an accidental coincidence within the limits 

 of a day must occur at times. Mr Milne, therefore, considers 

 the evidence he has collected as irreconcileable with the idea 

 that any connection exists betwixt the sources of subterranean 

 movement at these localities. Other observations have led 

 him to conclude, that even in cases where the seats of disturb- 



* Edinburgh New Philosophical Journal. No. 12, p 363. 



