in the length of the pendulum vibrating seconds. 34,7 
carefully adjusted previously to every observation. The pre- 
ceding detail may serve, with very little difference, for each 
of the stations, and I have been thus minute in my description 
of the various adjustments necessary, in order that no diffi- 
culty may be experienced by any who may use the pendulum 
after me. 
In observing the time of the transits, the chronometer was 
used, and was found to be particularly convenient from its 
beating half seconds. As soon as possible after the passage 
of the star, the chronometer was carefully compared with the 
clock, and the difference being applied to the time of the 
transit shown by the chronometer, and also the computed 
gain or loss of the clock during the interval between the 
observation and the comparison ; the time shown by the clock 
at the instant of the transit was obtained. 
These comparisons, as well as the whole of the data neces- 
sary for the examination of the results given in this paper, 
will be found in the Appendix. 
The climate of Unst, at the season when I visited it, is such 
as to render the opportunities for celestial observations ex- 
tremely rare. I had been informed, that the months of July 
and August were the most favourable, but on the contrary, 
I learnt on my arrival that they were considered the least so 
of any of the year, the atmosphere being generally clearest 
in May and September. Dense fogs and light rains suc- 
ceeded each other, rarely permitting a sight of the sun; and 
it was not until the 22d of July, that I was able first to observe 
the transits of a few stars. 
The following table contains the observations for the rate 
of the clock at Unst, derived from the table of transits given 
in the Appendix. 
