66 The Causes and Phenomena of Earthquakes. 



hydrodynamics of earthquakes. Nevertheless, the observation of 

 facts must be the foundation of our opinions as to the accuracy of 

 theoretical views. 



A catalogue of such facts has been made by Mr. Mallet, ex- 

 tending from 1606 B.C. to a.d. 1842, i. e., for 3448 years ; and 

 this is continued by Professor Perrey's annual register of earth- 

 quakes. The whole of the period up to 1850 has been discussed 

 by Mallet, and in these tables there is much to Tvhich the student 

 on earthquake literature may turn with advantage, for what is 

 more trustworthy than the usual gossip about such matters. I 

 find in the catalogues an observation of my own recorded of an 

 earthquake in 1834. 



Between 6000 and 7000 earthquakes bave thus heen brought 

 together, the area being co-extensive with land and ocean ; " and 

 nothing," says the compiler, " can be done better in this way till 

 observers shall have agreed to record facts observed on a general 

 plan, and referred to one central focus of collection for discus- 

 sion, taking advantage, for times of occurrence, of the means 

 offered by telegraphy." These records of distinct earthquakes 

 include numerous shocks at one time, as well as single shocks, 

 and in the case of the 2000 shocks said to have accompanied the 

 late volcanic outbreak of Mouna Loa, in the Sandwich Islands, 

 these 2000 would only be regarded as one. So that the docu- 

 mentary evidence is of greater value than at first appears. 



The discussion of so many as 6000 or 7000 odservations, or 

 10,000 as they are now, has led to some determinate opinions 

 which we must briefly pass in review. 



It may be submitted, that if earthquake shocks produce such 

 undulations as Hopkins describes ; and if they progress as the 

 Lisbon earthquake of 1755 proves they do, it is most certain that 

 the late shocks could not have come to us from southerly, north- 

 westerly, and north-easterly points at the same moment. They 

 ought, if the undulations were from one focus, to have diverged, 

 not converged. When explained the result is that the direction 

 was the same, from the north-east quarter. 



There are some results obtained from the discussion of Perrey's 

 catalogues, that almost startle the mind. This, for instance ; 

 that, allowing for the effect of closer observation in the more 

 recent periods, there is yet a presumption that observed earth- 

 quakes are and have been gradually increasing in number, and, 

 apparently, in intensity, from the beginning of our era to the 

 present time. 



Earthquakes. 

 Thus, up to the birth of our Lord, the total number 



recorded was . . ... ... ... ... ... 58 



From that to the end of 9th century, A.D. ... ... 197 



From 10th to end of loth 532 



