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XIX. On the difference of Meridians of the Royal Observatories 
of Greenwich and Paris. By Thomas Henderson, Esq. 
Communicated by J. F. W. Herschel, Esq. Sec. R. S. 
Read May 17, 1827. 
In the Philosophical Transactions for 1826, Part II. Mr. 
Herschel has given a detailed account of observations, which 
were made in the month of July, 1825, for the purpose of 
ascertaining the difference of the meridians of the Royal 
Observatories of Greenwich and Paris, with a computation of 
these observations, from which the most probable value of 
the difference of longitude appears to be p m 2i‘*6. But I 
have perceived that in the copy of the observations delivered 
to him from the Royal Observatory of Greenwich, an error 
of one second has been committed ; as the true sidereal time 
of the observation made there on 21st July, ought to be 
i7 h 38 ra 5712 in place of i7 h 38™ 56 s - 10, set down in the 
Table p. 104, which he informs me was computed at the 
Observatory, and officially communicated to him from the 
Astronomer Royal. This error seems to have had its origin 
in the little Table at the bottom of page 103 ; for, on sub- 
tracting the error of the clock, 47 s ’37, from the time 
i8 h 8 ra 30 s *40, the true sidereal time is i8 h 7 m 43 8 '03, instead 
of i8 h 7 ra 42 s, 03, there given. The error in the result of that 
day's observations, arising from this cause, has been partly 
compensated by a mistake of three tenths of a second, which 
