440 Different “ Rates” of Pennington’s Astronomical Clock, 
to the way in which he should wish the business to be conducted, 
or any detailed account of the state of the apparatus. He quitted 
Leith on his way home, the next morning; and on June 30th, I 
travelled from Leith to the Seadley Hills near Dundee, in order 
to acquaint Captain Colby with the state of affairs, and request 
him to suspend the operations in which he was there engaged, 
and accompany us to Zetland. To this he assented with that 
eagerness to promote the cause of science which has uniformly 
marked his character*. 
On cur arrival at the north of Zetland, as soon as the removal 
of M. Biot to Unst rendered it necessary for Captain Colby and 
myself to carry on our operations apart from that philosopher, 
we agreed that the captain with his assistant should undertake 
the observations with the zenith sector and the great theodolite, 
while I carried on those with the transit instrument and deter- 
mined the rate of the clock ; each, however, assisting the other 
in setting up the apparatus. Neither of us was at all aware that 
when the “ rate” of the clock was determined at Woolwich, the 
nut ab alone was screwed beneath the ball of the pendulum, and 
that the smaller nut ¢ d ¢’ d’, was simply applied during the voy- 
age, under the idea that it would serve to give steadiness to the 
former. This smaller nut has a neat milled-head which gives it 
every appearance of an ornamental finish to a constant part of 
the apparatus; and as such I continued to use it during the go- 
ing of the clock at Balta, simply taking care that it was brought 
up close to the nut a J, while 2¢ stood in its proper position, as 
ascertained by the indices I and I’. I made no computations of 
what might be the expected acceleration in latitude 60° 45’, lest 
their result should unconsciously bias my judgement in refer- 
ence to the experiment; but I knew very well, from my general 
recollections of the theory, that a clock which went truly at 
Woolwich, ought to gain from 35” to 40” per diem at Balta.. 
An acceleration, therefore, which fell short of my expectations, 
not merely by two or three seconds, but by from fifteen to twenty, 
could not but excite my astonishment. The observations of each 
succeeding day and night, convinced me that the rate was at least 
nearly correct ; so that, as I could neither detect nor conjecture 
any cause of variation in the clock, I began to suspect that there 
might be some latent cause in the geological structure of the 
* It is with reluctance I advert to such a trifle; but as it may serve to 
show the injustice of animadyersions which have been fre<ly indulged re- 
specting the dispositions with which we met M. Biot, I shall be excused for 
stating that while we were at Aberdeen in our way to Zetland, Captain Colby 
and myself procured for M. Biot’s use from our friends among the Professors 
at Marischal College, such magnetical and eudiometrical apparatus, as he 
thought himself likely to want when he arrived at the place of our ultimate 
destination. 
island. 
