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XX. Letter from Captain Basil Hall, R. N. to Captain Kater, 
communicating the details of experiments made by him and Mr. 
Henry Foster, with an Invariable Pendulum ; in London ; at 
the Galapagos Islands in the Pacific Ocean , near the Equator ; 
at San Bias de California on the N. IV. Coast of Mexico ; and 
at Rio de Janeiro in Brazil. With an Appendix, containing 
the Second Series of Experiments in London, on the Return. 
Read April 24, 1823. 
His Majesty's Ship Conway, 
My DEAR Sir, Spithead, 23rd February, 1823. 
X herewith transmit the details of the experiments which 
have been made with the invariable pendulum, placed in my 
hands by the Board of Longitude, at your suggestion. 
It is matter of regret to me, that I should have visited so 
many remote places, with such means in my hands, and have 
so few results to produce. The fact however is, that the ser- 
vice upon which I was sent had no connection with scientific 
research, and that it was only at casual intervals of active 
professional employment, that I had any leisure for enquiries 
of this nature. These occasional opportunies I owe to the 
generous indulgence of Sir Thomas Hardy, the Commander 
in Chief, to whose assistance, also, and encouragement in 
every pursuit having useful knowledge for its object, I stand 
essentially indebted. 
In drawing up the following account, care has been taken 
to state all the attendant circumstances, and to record in the 
Tables every observation in detail ; so that any person wishing 
to examine the work, may have the best means possible of 
estimating its value. 
