344 Capt. Kater's experiments for determining the variation 
Operations at Unst. 
I have remarked, that I selected for my experiments at 
Unst, an unfinished cottage, one of the walls of which was 
three feet thick. This was composed of irregular masses of 
serpentine, which I feared might be loosened by driving in 
the pickets to which the iron frame was to be screwed. 
Happily, however, I found the pickets act as wedges, and 
secure the stones more firmly in their places. The pickets 
driven into the wall were of oak, and were upwards of three 
inches in diameter, and more than a foot in length. To these 
the iron frame was firmly attached by its five screws, and on 
the evening of the 10th of July, I had the satisfaction of find- 
ing it as securely fixed as I could possibly desire. 
Two pieces of deal plank two inches and a half thick, were 
next fastened by long nails to the wall. To these the clock 
case was screwed at such a distance beneath the iron frame, 
as that the end of the brass pendulum might reach a little 
below the centre of the pendulum of the clock, and the clock 
was then put in heat , by moving the bottom of the case to the 
right or left, and when properly adjusted, the screws were 
tightened. The bell metal support was next put in its place 
and carefully levelled, and the pendulum lodged in the Ys 
elevated for that purpose. 
The triangular stand carrying the telescope, described in 
the paper on the seconds pendulum before referred to, was 
firmly screwed to pickets driven into the ground at about eight 
feet and a half in front of the clock ; and the Ys which sup- 
ported the pendulum being lowered till the knife edge rested 
on the agate planes, the diaphragm of the telescope was 
