340 
MAJOR SABINE ON TERRESTRIAL MAGNETISM. 
southern to the northern hemisphere, his observation of the weakest intensity was 
made in — 22^° in the meridian of 325°. In Mr. Dunlop’s passage from the North 
to the South Atlantic he observed the weakest intensity in — 27°, in the more easterly 
meridian of 339°. The three geographical positions in which these gentlemen must 
have crossed the line of least intensity will be found, on examination, in very near ac- 
cordance with my delineation of that line in the Philosophical Magazine for Fe- 
bruary 1839, which is repeated in the present map. 
Lieut. Suljvan crossed the line of no dip , as indicated by his observations, between 
the latitudes — 13° 50' and — 16° O', about the meridian of 324°, in his outward pas- 
sage; and between the latitudes — 15° 10' and — 15° 44', near the same meridian, in his 
homeward passage. Mr. Dunlop’s observations place that line in about — 13° lati- 
tude, in the meridian of 335° or thereabouts. These observations are also closely ac- 
cordant with the representation of the line of no dip laid down in the map referred 
to in the Philosophical Magazine, and repeated in Plate III. They add confirmation, 
if any were needed, to the non-identity of the lines of no dip and of least intensity, 
and to their wide separation in the part of the globe under consideration. This is a 
marked feature in the system of the magnetic lines at the present epoch, known for 
some years to those who have carefully attended to the progress of experiment, but 
not generally recognised till very recently. 
In addition to the observations of Messrs. Dunlop and Sulivan I have inserted in 
Plate V., in upright figures, the results of a series of intensity results obtained by 
Robert Were Fox, Esq., on the continent of Europe in 1838, by his own method of 
experimenting. The details of this series are given in the Appendix L. 
§ 2. Between the Cape of Good Hope and New South Wales. 
Mr. Dunlop’s observations (Appendix B.) furnish us with a series of dip and in- 
tensity results obtained at sea between the meridian of the Cape of Good Hope and 
New South Wales, and between the parallels of —35° and —41°; a part of the globe 
from whence no recent data at least have been obtained for the lines of dip, and where 
materials for the lines of intensity were previously wholly wanting. The form which 
the isodynamic lines assume in that quarter will admit of the connection being ap- 
proximately traced, between Mr. Dunlop’s intensity results and the positions of the 
lines in New South Wales as determined at several points of the coast by observa- 
tions already published, or which will be now communicated. This connection is 
shown in Plate VI., in which the intensity results are inserted in upright figures. 
The materials are too few, and too widely scattered, for the lines thus traced to be 
regarded as more than a first approximation ; but as such they may be useful. The 
form of the isoclinal lines in this part of the globe being less simple than that of the 
isodynamics, the materials are yet insufficient to admit of their being represented in 
any satisfactory manner; but the results themselves are inserted in the Plate in 
inclined figures in their respective localities. 
