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to be composed of an outer shell, having two magnetic poles, one in each hemisphere, and within the shell a solid nucleus or 'terrella,' having also two poles; and he further supposed that the terrella revolved round its axis, independently of the outer shell, and with a different velocity of rotation. By this arrangement a satisfactory explanation could be given of all the magnetic phenomena then known. Whatever value may attach to this conjecture as a physical theory, it undoubtedly possesses high merit as a recognition of the systematic and progressive character of the secular change, and as an assertion of the unquestionable truth that such effects must result from a cause equally systematic. In any case it was an earnest attempt to evolve law out of apparent confusion, and such attempts should, we imagine, meet at least with sympathy at our hands; certainly they deserve better treatment than to be dismissed contemptuously as geognostic dreams -a sneer unworthy of Humboldt. To Halley belongs the merit, most unquestionably, of having first recognised the fact that something more is necessary to explain the phenomena of terrestrial magnetism than the fixed magnetism of the globe itself.
In the absence of any evidence as to the existence of cosmical magnetic influences acting at the earth's surface, Halley naturally looked within the earth for a solution of his difficulties; but had he known what we know, that the position of the needle is influenced by the sun in his daily and annual courses, that it trembles in sympathy with every rent in his photosphere, and that the magnitude and frequency of these rents are connected with the configuration of the planetary system, it is scarcely possible to doubt that he would have recognised in cosmical action a machinery sufficient to account for all the phenomena of secular change. It is true we know not at present all the relations existing between the various parts of this complicated machine, nor the exact combination which finds its counterpart in the progressive magnetic changes at the earth's surface; still we have no doubt that here, as elsewhere, Nature will at length yield up her secrets to patient and honest inquiry. Forty years back, who dreamt of connecting the solar spots with magnetic disturbance ? and this discovery, important as it is, can yet only be considered as the first step towards the solution of the problem. The question still remains, what common cause is it which manifests itself simultaneously in such (apparently) very different forms, in bodies separated by an interval of nearly one hundred millions of miles? In its fipal shape the question will doubtless resolve itself into this, What is magnetism ? and here, possibly, we shall have reached the limit assigned to human inquiry in this direction. As the eloquent author of Modern Painters' has well observed, there is always a point where the cloud intervenes, and all beyond is shrouded in mystery.
But short of this ultimate form of the inquiry we see no reason to doubt that ail the laws and cosmical connexions which govern the magnetic phenomena on the surface of our globe will at length be completely unravelled, though many ages may elapse before the goal is finally reached. In the meantime it will be the duty of each succeeding generation to note carefully all the changes to which the magnetic elements are subject, by comparing their values with those which they had at former epochs. This is the object sought by the magnetic surveys, which of late years have been carried out over extensive portions of the earth's surface. The results of these surveys are made visible to the eye by charts, on which are traced the lines of equal declination, dip, and intensity. This mode of representation was first employed by Halley in his celebrated chart of the declination lines published in 1701, and has since been universally adopted. Such surveys,
when repeated at sufficient intervals of time, give the best means of tracing the march of the various lines over the earth's surface.
The first complete work of this kind was the survey of the British Isles, which was commenced in 1836 at the request of the British Association, and finished in 1838; the observations being reduced to the mean epoch 1837. The same Association, when assembled at Cheltenham in 1856, passed a resolution to the effect that it would be desirable to have the survey repeated, and appointed a committee to carry the resolution into effect.
This was done during the years 1858-61, so that 1860 became the middle epoch of the survey. The result has shown that even the comparatively short period of twenty: three years is quite sufficient to exhibit the changes which have taken place in the direction of the magnetic lines in these islands. The declination lines have moved towards the west, i.e. the westerly declination has diminished; the average annual rate of decrease at Kew being 7' 39" between 1858-62. The decrease, however, is being accelerated at the present time, and indications of this acceleration are shown during the four years in question, as the decrease was 6' 46" between 1858-9, and 8' 33" between 1861-2. The isoclinal lines were found to have increased the angle which they make with the geographical meridian by about 6° 17', having changed their direction from N. 65° 5' W. to N. 71° 22' W. ; showing that during the interval between the two surveys, the secular diminution of dip has been greater in the west than on the east side of the island. Thus at Lowestoft on the east coast, the average annual diminution had been 2:36, whilst at the Land's End it was 2:09. A similar change, but of smaller amount, was observed in the isodynamic lines, which had increased the angle which they make with the geographical meridian by about 2° 40', having varied in direction from N. 54° 54' E. to N. 57° 35':5 E. Hence we infer that in the northern parts of England the secular increase of the force had been greater than in the southern parts during the period in question.
It will be recollected that in the report presented to the British Association in 1838 special mention was made of the desirability of a magnetic survey of Canada. The establishment of an observatory at Toronto in 1840 afforded peculiar facilities for carrying out the recommendations of the committee. Accordingly in 1843–4 the survey was undertaken and successfully accomplished by Lieut. (now General) Lefroy, R.A. The interest attaching to this work arises from the fact that in the district surveyed is situated the North American Pole of greatest intensity. The position of this pole, as calculated from Lieut. Lefroy's observations, was found to be long. 260° 1' E., lat. 52° 10' N. The position of the Siberian Pole, as resulting from the survey of Northern Asia by Hansteen, Due, and Erman, is not so accurately determined. Its longitude in 1828–30 was probably about 115° E. Of its latitude we are still less certain, but at that time it lay probably somewhere between 63 and 70° north latitude.
Amongst the various surveys which have been made in recent times may be mentioned Captain Elliott's survey of the Eastern Archipelago in 1846–9, extending from 16° lat. N. to 12° lat. S., and from 80° to 120° long. E., Schlagintweit's survey of High Asia, extending from Galle in Ceylon, 6° 2' lat. Ñ. to the Karakorum pass, 35° 47' lat. N., and from Shikarpore, 68° 52' long. E., to Dibragarth, 94° 53' long. E., Dr. Lamont's surveys in France, Spain, and Bavaria, this latter, like the survey of the British Isles, being coextensive with the limits of the country, and complete in all the three elements. A survey of the West of France by the Rev. S. Perry, whence it appears that the mean annual secular decrease of declination between 1858–68 was 9'6, whilst from 1825–58 the mean annual decrease was only 5', showing a rapid diminution of declination, with a mean annual acceleraVOL. CXXXVI. NO. CCXXLVIII.
tion of .22. But of all works of this kind none can compete in importance with the great South Polar Survey (due to British enterprise alone), extending as it does from the South Pole to 40° lat. S. The results of this truly national undertaking have been discussed, and the positions of the magnetic lines for all the three elements laid down by Sir Edward Sabine in No. XI. of his invaluable series of Contributions ' to Terrestrial Magnetism,' a series forming by itself the most complete manual extant of the subject in its recent developments. We are glad to hear that an addition to the series has just been presented to the Royal Society in the shape of a similar survey of the Northern hemisphere, from the Pole to lat. 40° N., combining the results of all preceding partial surveys, and reduced to the same epoch 1842-5. The remaining space between lat. 40° N. and lat. 40° S. will doubtless in due time be filled up on the same plan—we trust by the same hand. We shall then possess, what has never been possible before, a complete representation of the magnetic state of our globe (as expressed by the lines of equal declination, dip, and intensity) corresponding to one and the same epoch. The basis will thus be laid for a revision of Gauss's
Allgemeine theorie des Erdmagnetismus,' which as originally applied entirely fails to give a correct delineation of the magnetic lines in the Southern hemisphere. This probably is the result of insufficient numerical data, which were for twelve meridional points on each of seven parallels of latitude, the greater part of which were in the Northern hemisphere, and of those in the Southern hemisphere none went beyond the twentieth parallel. It is not, therefore, to be wondered at, that fact and theory should be found so widely at variance in the middle and higher southern latitudes
. With an extension of the formula and corrected numerical elements, there seems no reason to doubt that the facts of both hemispheres will be given with equal accuracy. But, after all, we cannot disguise from ourselves that no theory can be accepted as final and satisfactory which does not contain within itself the means of adjustment to epoch, or, in mathematical language, which does not involve i explicitly. But to construct such a theory it will be necessary to know the cause or causes of the secular change; and to arrive at a knowledge of these causes, we must fully ascertain what are the experimental laws which govern the phenomenon; and as one of the first steps towards this is the determination of its period, the complete solution of the problem is probably reserved for a very remote future indeed.
ART. V.-1. Correspondence relative to the Fiji Islands.
Presented to Parliament. May, 1862. 2. Correspondence relative to the Deportation of South Sea
Islanders. August 10th, 1869; February, 1871 and 1872. 3. Correspondence and Documents relating to the Fiji Islands,
in so far as the same relate to their Annexation to the Colonial Empire of this country, or otherwise affording Protection to British Subjects resident in these Islands.
Presented to Parliament. August, 1871. During the past session of Parliament two questions con
nected with the islands of the Pacific Ocean, and especially with the Fiji group, have been prominently before the public, and have been more than once made the subject of legislative debate. The first and most pressing of these related to the practice entitled in Parliamentary Documents the Deportation of South Sea Islanders, which has been held by a large number of our fellow-countrymen to be nothing more or less than the polite phraseology to describe a system of entrapping and consigning to slavery these unfortunate creatures. Inasmuch as this system had, up to the present year, been mainly (though not exclusively) carried on by vessels sailing under British colours, the opinion had for some time been gaining ground that the honour of the British Empire was concerned in the suppression of a traffic which cannot be less nefarious in the Pacific than upon the west coast of Africa, or in other regions in which British blood and British money have been freely lavished for the same laudable purpose. It was therefore plain enough, during the session of 1871, that public opinion would support any attempt in this direction which might be initiated by Her Majesty's Government, and, indeed, the necessity of making such an attempt was earnestly urged upon them in the course of the debate upon a motion for papers upon the subject made by Mr. P. A. Taylor upon the 11th of August. În answer to the allegations made in the course of that debate, reflecting upon the conduct of the authorities of Queensland, the UnderSecretary of State for the Colonies, whilst defending the action of the Queensland Government, fully admitted the existence of the evils complained of, and announced the intention of Her Majesty's Government not only to present further papers upon the subject, but to invite legislation during the coming session of Parliament. The year, however, was not to terminate without an additional proof being afforded of the