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XVIII . — Experiments to determine the difference in the Number of Vibrations 
made by an Invariable Pendulum in the Royal Observatories of Greenwich 
and Altona. By Captain Edward Sabine of the Royal Artillery, Secretary 
to the Royal Society. 
Read March 25th, 1830. 
The invariable pendulum No. 12, with which these experiments were made, 
was vibrated in the Royal Observatory at Greenwich in July 1828 ; in the 
Royal Observatory at Altona in September and October of the same year ; 
and again at the Royal Observatory at Greenwich in August 1829. The mean 
of the results obtained at Greenwich, in July 1828 and in August 1829, give 
the rate of this pendulum at Greenwich, to be compared with its rate obtained 
at Altona. 
The experiments in July 1828 have been already printed in the Phil. Trans, 
for 1829, Part I. pp. 100-102 ; the result was as follows : 
Therm. Barom. Vibrations in Vacuo at 61°.5. 
61.50 . . . 29.446 . . . 85970.00 
In the experiments in August 1829 (Table A), the same barometer, thermo- 
meter, planes, and fixed support were used as in the preceding experiments. 
The rate of Graham’s clock employed in observing coincidences was supplied 
by Mr. Thomas Glanville Taylor by daily comparison with the Greenwich 
transit clock. The following is an abstract of the results in Table A. 
2 £ 
MDCCCXXX. 
