442 Different “ Rates” of Pennington’s Astronomical Clock, 
here spoken of the clock had been put up and taken down several 
times, and its different parts packed up in separate cases; 
that they had been exposed to the tossings of three rough and 
tedious voyages; and that the apparatus ‘had been subjected to 
experiment in summer’s heat and winter’s cold; the agreement 
of results at Woolwich before and after the expedition, and with 
the smaller nut on and off, is so great, as, in my mind, to pre- 
clude all doubt as to the accuracy of the compensation, or 
the general correctness of the ratio of lengths furnished by the 
pendulum, I have only tu add further, with regard to it, that 
during four months of the year 1818, and more than two soMnihs 
of the present year, in which [ have taken account of the rate of 
this clock, I have never found it to vary so much as half a second. 
If compensation pendulums could be always so constructed 
that the variations in their rate should be confined within as var- 
row limits as those which are recorded in this memoir; they 
would, I conceive, demaud the preference in all cases where com- 
modious and accurate comparison of the force of gravity in dif- 
ferent regions was the experimenter’s object. 
Having thus presented every fact that can possibly serve to as- 
sist the public in estimating how much or how little credit is due 
to the results furnished by Pennington’s clock in this inquiry, I 
most: positively disclaim ‘all uncandid sentiments while I point 
out concisely some defects, which in my Judgement attend the cor- 
responding experiments with the French apparatus, with which 
they have been so invidiously contrasteg. 
The apparatus employed by M. Biot is a slight modification 
of that which was contrived originally (I believ e) by Borda, and 
consists (besides the clock which serves to determine the oscilla- 
tions of the pended used in the experiment, by the method of 
coincidences) of four distinct parts. 1. A ‘knife-edge”’ suspen- 
sion which is supported by a horizontal plane having a longitu- 
dinal aperture. The knife is crossed in its middle, perpendicular 
to its edge, by a athall stem, at the top of which is a nut or but- 
jon, capable of being fixed higher or lower by the threads of the 
screw to which it is fitted; and thus of adjusting this part of the 
pendulum, when detarhed from the rest, to the same interval of 
oscillation as the entire apparatus. This is shown at fig. 2. 
where KE is the ‘* knife edge,” SB the stem projecting both 
above and helow it, S the screw, and N the nut which by work- 
ing upon it serves to regulate the time of oscillation. 2. A very 
fine metallic thread, of "equal diameter in the whole of its length, 
which is attached by its upper extremity to the extremity B of 
the stem, by a small screw. 8. A small hollow segment or cup, 
to the interior of which a ball of platina or other ‘metal adheres 
by means of a thin coating of a greasy substance; the cup being 
attached 
