144 Mr D. Milne on Earthquake-Shocks felt in Great Britain, 



a sto//;?^ direction ;" and he accordingly afterwards describes 

 it as '• the angular jolt or roll upwards." 



These differences in the direction in which, at different 

 places, the shock came upwards to the surface, are all quite 

 intelligible, on the hypothesis offered in a previous part of this 

 memoir,* that it is the effect of a vibration transmitted through 

 the crust of the earth, and they serve, therefore, to confirm 

 the correctness of that hypothesis. 



On the same hypothesis, an easy explanation is afforded of 

 a number of other facts, to be found in the reports before 

 quoted. Thus, the clattering of slates on house-roofs, w^ould 

 be produced by the transmission of vibrations upwards 

 through the earth's strata and the solid walls of the building. 

 The projection of m.asses of rock from the south slopes 

 of the Ochils, Damiat, and Castle Rock of Edinburgh (all of 

 these places being to the south of Comrie), is, on the same 

 principle, quite intelligible. For the same reason, at places 

 situated east of Comrie, the east gables of houses were neces- 

 sarily the most damaged, — whether by being rent horizontall}^ 

 or by being made to lean over towards the east : — the west 

 gables, by abutting against the front and back walls, were 

 much better able to withstand an impulse from the westward. 

 Hence, also, the general violence of the shocks was more felt 

 by people in the upper, than in the lower flats of houses. 



In a great number of the reports, it is remarked that the 

 undulations were most striking in carse or alluvial grounds, 

 though the accompanying noise was not so great there as in 

 rocky ground. If the noise alluded to, be that produced in the 

 earth, it is obvious that there would be none where there were 

 no materials capable by attrition of producing noise. With 

 regard to the undulations, they would obviously be more easily 

 formed in places where the ma,terials were flexible, and thus 

 capable of yielding to impulses from below. 



7. Among the accounts of the shocks which occurred in 

 October 1839, there will be found observations of some ano- 



♦ See Ed. Phil. Journ. vol. XXXI. p. 276. 



