III. The Bakerian Lecture.— A Magnetic Survey of the British Isles for the Epoch 
January 1, 1886. 
By A. W. Rucker, M.A., F.R.S., cmd T. E. Thorpe, B.Sc., Ph.D., F.R.S. 
Lecture delivered April 11,—MS. I’eceived June 0, 1889. 
[Plates 1-14,] 
Contents. 
Page. 
Introduction—References to Former Surveys.5.5 
Defects of Former Surveys.55 
Scope of the Survey; Choice of Stations. .56 
Epoch.56 
Instruments used.56 
Eew as Base Station.57 
Comparison of Kew and Survey Instruments.58, 59 
Units employed.59 
Comparison of Survey Instruments under N’ormal Conditions in Fiel l.60 
Chronometers and Method of Determining Rates. 61 
Number of Stations; Average distance apart.62 
IMethod of Taking the Observations (Adjustment of Mirror, &c.).6.3, 64 
Discussion of Diurnal Variation and Disturbance.64-69 
IMetbod of Tabulating the Observations.69-76 
Meaning of Symbols used. 70 
Example of Declination Form. 71 
Horizontal Force : Indejjendent Results. 72, 73 
,, ,, Specimen Form. . 74 
Inclination. 76 
Errors of Experimenl.76-80 
Declination. 78 
Horizontal Force. . . 78 
Inclination.79,80 
Secular Corrections.81-9.3 
In Dip.81-87 
In Declination.87-91 
In Horizontal Force. 91-93 
Form of Pi’esenting Results of Observations.9.3-95 
Description of, and Results at, each Individual Station . . '. 95-232 
Calculation of the Isomagnetic Lines :— 
The Isogonal Lines. 23.3-244 
Terrestrial and Tine Isomagnetics. . 233 
Three Classes of Disturbances. 23.3 
MDCCCXC.—A. 
5.7.90 
