392 TEERESTKIAL MAGNETISM. 



Geographicul Society; one in LSTS by tiie late Cai)t. Sir Frederick 

 Ev^an.s, and another in 1897 by Sir Arthur Kiicker. And I would here 

 quote the opinion of Doctor Mill, when defining geography, in my sup- 

 port: '■'Geography i.s the science which deals with the forms of the 

 eartli's crust and with the influence which these forms exercise on the 

 distril)ution of other phenomena." 



We know now that the normal distribution of the earth's magnetism 

 for any epoch is in many localities seriously affected according as the 

 natuic of the country surveyed be mountainous, or generally a plain, 

 in the form of islands (or mountains standing out of the sea), and 

 from land under the sea. There is also reason to suspect that the mag- 

 netism of that portion of the earth covered by the oceans difiers in 

 intensity from that of the dry land we inhabit. A connection between 

 the disturbances of the elirtirs crust in earthcpiakes and disturbances 

 of th(^ magnetic needle also seems to exist, although, the evidence on 

 this point is not conclusive. 



MACXKTK" SURVEYS. 



Previously to the year LSSO there were two periods of exceptional 

 activity on the part of contril)utors to our knowledge of the earth's 

 magnetism, during which the scientific sailor in his ship on the track- 

 less ocean combined with his brethren on land in making a magnetic 

 surve}' of the globe. 



The first period was that of lcS-f8-l84l), during which not only were 

 fixed observatories established at Toronto, Saint Helena, Capetown, 

 and Hobart for hourly ol)servations of the movements of the magnetic 

 needle, but to use Sabine's words, "that great national undertaking, 

 the magnetic survey of the south polar regions of the glol^e,"' the fore- 

 '?r of our present antarctic expedition, was accomplished by Ross 

 and his companions almost entirely at sea. 



This antarctic survey was carried out during the years 1840-1845, 

 and the results given to the world as soon as possible by Sabine. The 

 results afterwards formed a valuable contribution when constructing 

 his maps of equal lines of magnetic declination, inclination, and inten- 

 sity for the whole world, a great work for the completion of which 

 Sabine employed every available ol)servation made up to the year 1870. 

 whether on land or at sea. 



Readers of these contributions can not fail to ])e struck with the 

 great number of observations made by such travelers as Hansteen and 

 Due, Erman and Wrangel, extending from wt^stern Europe to far 

 into Sil)eria. 



The second period was thjit of 1S70-1SSU, during which not only was 

 there nmcli activity among observers on land, but that expedition, so 

 fruitful to science, the voyage of II. M. S. ClidUenijir^ took place. 

 During the years 1872-1876 we find the sailor in the CJtalloKjcr doing 

 most valuable work in carrying out a magnetic surve}" of certain por- 



