C MR. A. W. RtTCKER AND DR. T. E. THORPE ON A MAGNETIC 
Organization and Staff. 
All the gentlemen who have aided us in the extension of our original survey have 
been selected either from among the Assistants in the Royal College of Science, 
London, or from among those who have gained the Associateship of the same 
College. 
In 1890 we appointed Messrs. A. E. Briscoe, B.Sc., and P. L. Gray, B.Sc., to aid 
us in the work of observation. ]\Ir. Briscoe resigned his appointment at the end of 
that year, and was succeeded by Mr, W. Watson, B.Sc., who, with Mr. Gray, worked 
in the field durino- the summers of 1891 and 1892. 
Each of these gentlemen, having been instructed in the use of the instruments and 
methods of reduction, made a series of test observations at Kew, and then undertook 
a short preliminary tour, the results obtained in which were at once completely 
reduced, so that their accuracy could be tested. Having passed satisfactorily through 
this course of training, the observers entered upon prolonged courses of field work, 
extending, in 1891 and 1892, over the six summer months. The figures given here¬ 
after prove that their observations were of the most trustworthy character, and 
attained a very high standard of accuracy. 
The work of reducing the observations made, generally in duplicate, and frequently 
in triplicate, at many hundreds of stations, was very heavy. The observers took a 
leading part in this, but we also organized a small body of computers, by whose aid 
the task of reduction was as far as possible completed very shortly after the observa¬ 
tions were made. The method adopted was as follows :— 
The observers always reduced their observations within a day or two, and forwarded 
them to one of the staff of computers, wdio verified the calculations and made a fair 
copy. In the autumn, when the field work for the season was completed, the observers 
checked the accuracy of any alterations which had been made in their original calcu¬ 
lations by the computers, and the observations made at some of the stations were 
reduced, de novo, either by Professor PtfiCKER or by Messrs. Gray and Watson, to 
make sure that no error affected a whole series of reductions. 
The value of “P” in the formula for the horizontal force was then found, and the 
corrections for magnetic disturbances were applied by means of the curves obtained 
from the Kew self-registering instruments. 
Every step in the calculations was checked by an independent computer, and we 
believe that no errors of any importance have escaped detection. The equations to 
the iso-magnetic lines were determined by Professor Bucker, but the heavy work of 
testing and applying them was performed entirely by Messrs. Gray and Watson. 
These gentlemen have done the work assigned to them, both as observers and as 
computers, with great ability, energy, and zeal, and our hearty thanks are clue to 
them for the faithfulness, patience, and scientific skill with which they have 
assisted us. 
