74 REPORT — 1876. 



Seventh Report on Earthqualces in Scotland, drawn up by Dr. Bryce, 

 F.G.S., F.R.S.E. The Committee consists of Dr. Bryce, F.G.S., Sir 

 W. Thomson, F.R.S., J. Brough, G. Forbes, F.R.S.E., D. Milne- 

 Home, F.R.S.E., and P. Drummond. 



Tke state of quiescence alluded to in last year's Report has suffered 

 scarcely any interruption during the current year. No movement has oc- 

 curred of sufficient intensity to affect any of the instruments employed by 

 the Committee for testing the shocks. The Association wiU be aware that 

 these are the seismometer, constructed on the principle of the inverted pen- 

 dulum, which is placed in the tower of the parish church of Cpmrie, and two 

 sets of upright cylinders, described in last year's Report, Avhich stand on 

 boards on the sanded floor of a building erected two years ago by the Asso- 

 ciation upon a site, half a mile west of the Comrie church, kindly granted by 

 P. Drummond, Esq., of Dunearn, in the grounds surrounding his house. 

 This building stands in the Comrie valley, on a boss of rock of the same 

 kind of slate of which the adjacent hills and ridges arc composed, and which 

 can be traced into continuity with those on both sides of the valley. It Avas 

 therefore expected that cylinders so placed would readily respond to any 

 movement affecting the rocks on either side of the valley, more especially 

 as the centre or focus from which it has hitherto been considered that the 

 movements have emanated is at no great distance on the north side of the 

 valley. 



This expectation has not been realized, inasmuch as two slight shocks were 

 experienced on the 14th and 16th of January, in the morning and afternoon, 

 without affecting the seismometer or the cylinders, even those of smallest dia- 

 meter, which a very slight movement is sufficient to lay prostrate in the sand. 

 It is easy to see that a very extreme sensibility must be avoided in order to 

 guard against the effects of other disturbing causes — as a storm of wind, a 

 peal of thunder near at hand, or a heavy footfall on the rock outside ; and 

 hence that an undulation, propagated from a distant centre, might be so 

 retarded by the resistance of rocky masses as not to produce the required 

 amount of distui'bance. The evidence furnished by several most intelligent 

 and trustworthy persons leaves no doubt that on the day mentioned a very 

 slight shock was reaUy felt on the north side of the valley ; that the move- 

 ment seemed to come from the westward, and was attended by a slight 

 noise, which died gradually away towards the south-east. 



This somewhat disappointing result has led your Committee to add two 

 more cylinders of increased delicacy to each set, and to use every effort to 

 obtain suitable sites for other sets more to the west and north, and also 

 further down the valley, as near Dunira, the conjectured focus, and that 

 fixed on by Mr. Milne-Homo in the former inquiry, in Glen Lednoch near 

 the edge of the eruptive granite tract, whence the late disturbance seems 

 to have proceeded; and, if possible, also at Ardoch, Dunblane, and Bi-idge 

 of AUan, at all of which the shocks of 1873 were so severely felt. The 

 expense would be inconsiderable ; the difficulty to be encountered is the 

 procuring of a suitable and safe site and a competent observer. Your Com- 

 mittee earnestly hope that these obstacles will be overcome in the course of 

 the succeeding year. 



