48 BEPORT 1841. 



marking down all the shocks which had occurred since October 1839, and 

 who had himself contrived and constructed several ingenious instruments for 

 indicating the shocks. 



The three instruments were erected in Comrie and the immediate neigh- 

 bourhood. The largest of those on the principle of the inverted pendulum 

 is in the town of Comrie, and is fixed inside the steeple of the parish church. 

 The other instrument on the same principle is at Comrie House, situated about 

 a quarter of a mile to the north of Comrie, and taken care of by Colonel 

 Simpson, who resides there. The remaining instrument is at a place called 

 Garriechrow, close to Cluan Hill, about two miles west of Comrie, and is under 

 the immediate charge of the overseer of Sir David Dundas, Bart., of Duneira. 



These instruments were erected a few days before the 1st of January 1841. 

 They have been affected only twice, viz. on the 10th and 22nd of March 184'1. 

 On the first occasion both of the inverted pendulums had their upper extremi- 

 ties thrown to the west half an inch, where they remained till examined. On 

 the other occasion they were again thrown to the west, but scarcely half an 

 inch. The simple pendulum at Garriechrow has not been affected, and is 

 thought to be not sufficiently sensitive. 



The following inferences seem deducible from the way in which the in- 

 struments were affected on these two occasions: — (1.) There was, on both 

 occasions, a sudden horizontal movement of the ground where both instru- 

 ments were placed, indicated by the extremities of them being thrown off 

 their centres. (2.) This horizontal movement, on both occasions, was to- 

 wards the east. (3.) The amount of this displacement of the ground was, on 

 the first occasion, half an inch ; on the second, less than half an inch. 



This last-mentioned inference vvas confirmed by the feelings of those who 

 perceived both shocks, as they considered that the first was the most severe, 

 though neither was nearly half so severe as the shock of October 1839. 



Mr. Macfarlane states, however, that on both occasions there was a move- 

 ment of the earth's crust not indicated by the instruments. He alludes to a 

 vertical movement that was sensibly felt, and which on the last occasion was 

 indicated by one of his own instruments. 



This circumstance has been alluded to, to show the propriety of having 

 instruments of a different kind from the above. Several have occurred to 

 members of the Committee calculated for vertical movements ; and these 

 movements it is of some consequence to have marked and measured, as it is 

 believed they are always produced at Comrie when a shock occurs, and even 

 in cases when there may be little or no horizontal movement. 



It is also to be observed, that there is strong reason to believe that the 

 Comrie shocks emanate from a particular spot, the exact position of which 

 can only be ascertained by a number of instruments placed around the sup- 

 posed locality. 



It is hoped, therefore, that the Association will continue the appointment 

 of a Committee, and give a renewed grant of money for procuring instru- 

 ments and registers. From what has been said, it must be evident that the 

 object which was last year thought worthy of being prosecuted cannot be 

 properly attained without a greater number of instruments, and some of them 

 calculated to indicate vertical movements of the ground. It is also necessary 

 that they should be much more sensitive than those now used ; for, though 

 there were only two shocks indicated by the instruments, Mr. Macfarlane 

 reports, that from the 1st January 1841, when they were in operation, to the 1st 

 July, there were no less than twenty-seven shocks distinctly felt at Comrie. 



It is unnecessary to refer, in this Report, to the reasons which induced the 

 Association last year to have a regular register of the earthquake shocks oc- 



