A Magnetic Sur vey of the British Isles for the Epoch January 1, 1891. 
By A. W. Rucker, M.A., E'.R.S., and T. E. Tiiorpe, D.Sc.. LL.D., E\R.S. 
Ivcceivccl June 21,—Read June 21, 1&94. 
[Plates 1-14.] 
Contents. 
Introduction . .. 
Organization and Staff. 
Observers. . 
Computers. 
Epoch of Survey. 
Magnetic Units Employed. 
Instruments. 
Base Station—Kew. 
Survey Standard, 1886 . 
Discrepancies of Standard Instruments. 
Reasons for assuming the Kew Standards to be Constant. 
Methods of Coi'recting for Diurnal Vai-iation and Distnibance used in 1886 
and 1891 . 
Comparison of Kew and Survey Insti’uments. 
Declination.. 
Table of Corrections to Declinometers. 
Magnitude of the Cori’ections. 
Horizontal Force. 
Table of Corrections to IMagnetometers. 
Dip. 
Reasons why Coriectioiis are Unnecessary. 
Summary of Differences between Kew and Survey Standards. 
d'ime Signals. 
Selection of Stations. 
Work of the Different Observei-s. 
Total Number of Stations. 
Total Number of Observations.. 
Positions of Stations. 
IMethod of Taking the Observations.. 
Correction and Tabulation of the Observations. 
Table of Values of “ P ”. 
Errors of Experiment. . 
Secular Coi-rections for the Reduction of the 1891 Survey to Epoch. 
MDCCCXCVI.—A. h 
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