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VIII. Account of a series of observations, made in the summer of 
the year 1825, for the purpose of determining the difference of 
meridians of the Royal Observatories of Greenwich and Paris ; 
drawn up by J. F. W. Herschel, Esq. M. A. Sec. R. S. 
Communicated by the Board of Longitude. 
Read January 12, 1826. 
Operations having been carried on to a considerable extent 
in France, and other countries on the continent, for the 
purpose of ascertaining differences of longitude by means of 
signals, simultaneously observed at different points along a 
chain of stations ; and the Royal Observatory at Paris, in 
particular, having been connected in this manner with a 
number of the most important stations, it was considered 
desirable by the French government that the Royal Observa- 
tory at Greenwich should be included in the general design. 
The British Board of Longitude was accordingly invited to 
lend its co-operation towards carrying into effect a plan for 
that purpose ; and the invitation being readily accepted on 
their part, I was deputed, in conjunction with Capt. Sabine, 
in the course of the last summer, to direct the practical 
details of the operation on the British side of the channel, and 
to make the necessary observations. Every facility was 
afforded us in making our dispositions, on the part of the 
different branches of His Majesty's government to which it 
was found necessary to apply. A detachment of artillery 
was placed, by his Grace the Duke of Wellington, Master 
