246 



THE GEOLOGIST. 



that the particular spot from which the earthquakes emanate, 

 is situated about one mile N.E. of Duniva House, and one 

 and a half or two miles N.W. of Comrie ; and it is consi- 

 dered desirable to place additional instruments at Duniva, 

 and in the neighbourhood, with the view of approximating 

 still nearer to the exact spot of emanation. 



The additional instruments for indicating earthquake 

 shocks, lately sent out, are seven in number. 



1 . Four of these are on the principle of the watchmaker's 

 noddy, explained in the last year's Report. 



2. Another instrument consists of four horizontal glass 

 tubes slightly turned up at each end, and filled with mer- 

 cury. These tubes are laid down on the solid floor of a 

 room, according to the 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 no hori- 

 zontal movement, but an inclination of the ground only, the 

 mercury will flow out of the tube or tubes affected by the 

 incUnation. This instrument was made by Mr. Newman, 

 of London, under the directions of Professor Wheatstone 

 and Mr. D. Milne. 



3. The two remaining instruments are intended exclu- 

 sively to indicate vertical movements of the ground. They 

 consist of a horizontal bar, fixed to a soHd wall, by means 

 of a strong flat watch-spring, and are loaded at the opposite 

 end. If the wall suddenly rises or sinks, the loaded end of 

 this horizontal rod remains from its vis inertice nearly at 

 rest, and thus can move any light substance (as paper or a 

 straw) brought against it by the vertical movement of the 

 ground; the light substance being so adjusted as to remain 

 fixed wherever the rod moves it. 



Beside the above instruments, a barometer, a double ther- 

 mometer, and a rain-gauge, have been sent to Mr. Macfar- 

 lane, of Comrie, in order that the state of the atmospliere 



