94 report — 1842. 



will now mention what additional instruments have been sent there, and to 

 whose charge they have been entrusted. 



The additional instruments for indioating earthquake shocks are seven in 

 number. 



Four of these arc on the principle of the watchmaker's noddy described in 

 last year's Report. 



Another instrument consists of four horizontal glass tubes, slightly turned 

 up at each end, and filled with mercury. These tubes are laid down on the 

 solid floor of a room, according to the different points of the compass; and 

 it is expected that, when a shock takes place, the mercury will flow out of 

 one or more of these tubes. If there is a horizontal movement of the earth's 

 surface, say in a direction from W. to E., the mercury will flow out of the 

 west end of the tube placed in that direction, and partially out of two 

 other tubes. If there is no horizontal movement, but an inclination of the 

 ground only, the mercury will flow out of the tube or tubes affected by the 

 inclination, and probably in a larger measure from the ends of the tubes to- 

 wards the dip. This instrument was made by Mr. Newman of London, under 

 the directions of Professor Wheatstone and Mr. Milne. 



The two remaining instruments are intended exclusively to indicate any 

 vertical movements of the ground. They consist of a horizontal bar, fixed 

 to a solid wall by means of a strong flat watch-spring, and loaded at the op- 

 posite end. If the wall suddenly rises or sinks, the loaded end of this hori- 

 zontal rod remains, from its vis inertia, nearly at rest, and thus can move any 

 light substance (as paper or a straw) brought against it by the vertical move- 

 ment of the ground, and which light substance is so adjusted as to stick 

 wherever the rod leaves it. 



One of this last mentioned class of instruments, and the one formed with 

 glass tubes, have been set at Comrie, in the upper story of a house occupied 

 by Mr. Macfarlane, post-master there, — a very intelligent person, and most 

 anxious to aid the Committee in their inquiries. He has kept an accurate 

 register of all the shocks felt at Comrie during the last three years. 



In regard to the instruments formed on the principle of the watchmaker's 

 noddy, one of them has been placed at Crieff (six and a half miles east of 

 Comrie), under the charge of the Rev. Mr. M'Alester. A second has been 

 placed at St. Fillans (a small village five and a half miles west of Comrie) 

 under the charge of the Rev. Mr. Logan. A third is placed at Invergel- 

 die, about five miles north of Comrie, under charge of the farm-overseer 

 there. A fourth instrument of this kind is about to be sent to Kinlochmoi- 

 dant, near Strontian in Argyleshire, where shocks are occasionally felt. It 

 is to be taken charge of there by Wm. Robertson, Esq., the proprietor of 

 Kinlochmoidart. To the same place there is to be sent one of the horizontal 

 bars intended to indicate vertical movements of the ground. 



Besides the foregoing instruments, others of a meteorological character 

 have been placed at Comrie, in order that the state of the atmosphere at the 

 moment of the shocks, and the nature of the weather generally during their 

 occurrence, may be as nearly as possible ascertained. These instruments 

 consist of a barometer, double thermometer, and a rain-gauge. They are 

 under the charge of Mr. Macfarlane of Comrie, by whom their indications 

 are regularly registered. 



III. The Committee will next notice any effects produced on the instru- 

 ments, during the course of last year, by earthquake shocks. The instru- 

 ments sent lately by the Committee have not yet been affected, having been 

 but a short time at their respective stations. Those which have been af- 

 fected, were the instruments sent last year. 



