28 
MR. A. W. RUCKER AKD DR. T. E. THORPE OX A MAGXETIC 
the Admiralt}^ for the loan of chronometers, and Mr. Peeece, F.R.S., Chief Engineer 
to the Post Office, and Mr. J. C. Lamb, the Head of the Telegraph Department, for 
the facilities afforded us for checking the chronometers by means of the telegraphic 
time signals which are daily sent to all jDOst offices in the kingdom. In spite of the 
very large number of places at which it was desirable to receive the signal, the 
officials were warned when to expect the request for “ time,” as well as instructed to 
comply with it. As the rules ordinarily in force against the admission of unauthorised 
persons to the telegraph offices are, very properly, stringent, the hearty support 
we received from the Heads of the Department was essential and of great service. 
Selection of Stations. 
As we intended to increa,se the number of stations very largely, it was of course 
desirable that the new observations should be used in determining the terrestrial 
iso-magnetics. 
We therefore decided that in 1890 and 1891 the country should be covered with a 
new network of stations fairly uniformly distributed over it, and that the results 
should all be reduced to January 1, 1891, so that the secular correction, being applied 
for a few months only, should be relatively unimportant. 
From these observations, the terrestrial iso-magnetics for January 1, 1891, were 
determined, and the Disturbances and Disturbing Forces calculated and mapped. 
This wmrk wms completed by March, 1892, so that we were able to select the j^laces 
at wdiich observations were to be made in that year, with a full knowledge of the 
results which had already been obtained, and therefore in such positions as were 
likely to afford the most valuable information. 
The work of observing was divided as follows :— 
In 1890 Messrs. Gray and Briscoe observed in England and Wales; 
In 1891 Mr. Gray travelled in Ireland and Mr. Watson in Scotland; and 
In 1892 Mr. Watson w'ent to Ireland and Mr. Gray to Scotland. 
In both 1891 and 1892 a number of additional observations were made in England 
as the observers went to or returned from their more distant stations. 
By interchanging observers and instruments we have aimed at preventing any 
systematic error, however small, affecting any part of the area of the survey. 
In 1889 we ourselves made the two supplementary surveys in the West of 
Scotland and in Yorkshire and Lincolnshire, to which reference has already been 
made. Our thanks are due to Professor Beinold, F.B.S., who accompanied 
Professor Bucker during part of this tour, and made a number of Dip observations. 
In 1890 we worked together and ran a chain of stations across the country from 
London to Penrith. 
In 1891 and 1892 Dr. Thorpe observed in Scotland and the Western Isles, and in 
1892 Professor Rucker added some stations in the Midlands. 
