54 
ME. A. W. RtiCKER AND DR. T. E. THORPE ON A MAGNETIC 
Page. Page. 
Method of obtaining Equations to Tsomagnetic Lines . . . 234, 235 
Objections to Method of Least Squares.236 
“ Central Stations ”.237 
Declinations calculated from the District Lines for Points 
Uniformly Distributed over the Area of the Survey (Table) 238, 239 
Formula for calculating Declinations.240 
Discussion of Isogouals on Borders of English and French 
Surveys . 241-244 
The Isoclinal Lines. 244-246 
Formula for calculating ditto.245 
The Isodynamic Lines. 247-250 
Necessity for Two Formulfe.243 
Eormulte for calculating Horizontal Force.250 
Summary of Elements and Disturbances. 251-258 
Scotland. 251, 252 
England and Wales. 253-256 
Ireland. 257, 258 
Sujiplementai’y Stations.258 
Discussion of Local and Regional Disturbances :— 
Methods of deducing Disturbances. 259-269 
Effect of Disturbing Centre on Isogonals. 261, 262 
,, „ ,, other Lines. 263,264 
“ Ridge ” and “ Valley ” liines.265 
Meaning of Vertical Force Disturbances Doubtful.266 
Results at Different Stations at Different Times .... 267-269 
Table of Disturbing Forces. 270-273 
Surveys of Selected Districts. 274-292 
The Malvern Hills. 274-276 
The Island of Canna. 276-279 
The E. and S.E. Counties. 280-286 
The Wash. 286-288 
The Leicestershire District. 288-292 
General Results of Investigation of Disturbances. 292-314 
Methods of Testing Conclusions. 292 
Comjjarison with Mr. Welsh’s Survey.293 
Declination at Stations common to the Surveys of 1857 
and 1886 294-296 
Disturbing Forces in Scotland (Welsh) - . 297-299 
The Highland District. 299-302 
The Scotch Coalfield District. 302, 303 
N.W. England, N. Wales, and Galloway. 304-306 
N.K England. 306-308 
The Southern District. 308, 309 
Ireland. 309, 310 
Magnetic Map of United Kingdom.310 
Relation between Magnetic and Geological Constitutions 
of Districts.310-314 
The Causes of Local and Regional Magnetic Forces . . .. 314-320 
Dr. Naumann’s Views.314 
Eai’th-currents.315 
Insufficiency of observed Earth-currents to Produce Effects 316-318 
In.sufficiency of Geological Faults. ... 318 
