so, the magnetic force diminished as the latitude increased; showing that even the most southerly of the stations (between the parallels 60° and 70°) was north of the point of greatest intensity. But the dip in the same localities increased with the latitude between these same parallels. Hence it was evident that the points of maximum dip and maximum force were not coincident. This discovery may be regarded as the first fruits of England's renewed interest in magnetic research. Of course it involves the fate of supposition No. (1.), even if there were no direct evidence on the point. But, in fact, we have very accurate determinations of both the line of no dip and the line of least intensity, and a single glance is sufficient to show that their courses are systematically discordant. In one part (to the west of Africa) they are separated by 20° of latitude, or about 1,200 geographical miles!

The next magnetic discovery in the north polar regions, due to the same series of British expeditions, was that of the point where the dip-angle=90°, or, as it is usually called, the Magnetic Pole. This discovery was made in 1831 by Sir James Ross, and the position of the point in question, according to his determination, is Lat. 70° 5' 17" N. and Long. 96° 45' 48" W. We must here state, in passing, that the term magnetic pole seems to us objectionable, as being connected with the untenable hypothesis of a single magnetic axis of the earth. It has been sometimes proposed to use the term pole of verticity, to distinguish it from the points of greatest intensity. This would be undoubtedly a better name for a point which has nothing very remarkable about it, except as being the point where the direction of the earth's magnetic force coincides with that of gravity; and as there is no known connexion between these two forces, it is difficult to understand why, in the present state of the science, so much importance should be attached to it. In the early days of science, if science it could be called, before the period of inductive research, when speculation ran riot, and fancy piled up huge masses of magnetic rock round the geographical poles, it was naturally supposed that here all the difficulties of the subject would receive their solution; and we can understand the term 'magnetic pole,' and the interest attaching to these regions. Even after the 'rock' theory was exploded, which for the credit of science, we are happy to add, was at a very early date (Gilbert, in his work De Magnete,' in 1633, ridicules the idea as utterly unphilosophical), the interest attaching to these points was revived, by their supposed coincidence with the points where the magnetic force is the greatest. But now, when this illusion also has been dispelled,

and they are known to coincide neither with the geographical poles, nor with the points of maximum intensity, it really does seem strange to meet with writers who, in works of a professedly scientific character, still speak of the two magnetic 'poles, and that without a word to limit the meaning and application of the term. If it be used in its original sense, it can only mislead; and if it be used merely as a term, this should be stated, and then it may take its place by the side of vis-viva,' and many other terms in our scientific vocabulary, which still do good service as such, having long survived the fallacies which gave them birth.

In the year 1819 a fresh impetus was given to the study of terrestrial magnetism by the publication of Hansteen's remarkable work, Magnetismus der Erde,' in which from the facts of the declination he showed the impossibility of reconciling these facts with the then universally accepted doctrine of a single magnetic axis of the earth, having two poles, one in each hemisphere. But in truth this discovery really dates from 1683, and is due to our own countryman, Halley, who, notwithstanding the limited number of observations then available (and these confined solely to the declination), was able to detect the true features of terrestrial magnetism, and showed that the facts before him clearly implied the existence of four poles or centres of maximum force on the earth's surface. So much interest did the revival of this theory by Hansteen excite in his own country, that the Norwegian Storthing fitted out an expedition in 1828 for the purpose of testing by actual observation the conclusions he had arrived at as to the existence of a pole of intensity in Siberia. This expedition, under Hansteen and Due, traversed the whole of Northern Europe and Asia as far as Irkutsk, descending the Obi and Jenesei to the Arctic circle. Another well-known explorer, Erman, was traversing the same region at the same time, and the result of their combined labours was to establish fully the truth of Hansteen's anticipations as to the existence of a Siberian Pole of intensity.

The year 1828 was also memorable as the commencement of what may be called a new era in the history of magnetic investigation, and its hero was the Baron Alexander Von Humboldt. As far back as the beginning of the present century he had become convinced, as he tells us, that continuous observations at short intervals for several days and nights would yield a richer harvest than the single observations of many months. He, therefore, in 1806-7, in conjunction with his friend Oltmanns, commenced at Berlin a series of hourly, and often half-hourly,

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observations on the movement of the needle for five or six days and nights in succession, principally at the times of the equinoxes and solstices. It was not long before he observed the recurrence, often at the same hour, for several nights together, of irregular perturbations of the needle, to which he gave the name of magnetic storms. In the absence of any previous observations on this class of phenomena, being uncertain whether or no these storms' were of a purely local character, he was led to desire the establishment of stations east and west of Berlin, where similar observations might be carried on simultaneously. The disturbed state of Europe prevented the fulfilment of his wishes at the time, and it was not till his return to Berlin, after an absence of eighteen years, that he found means to accomplish his long-deferred project by carrying on a series of continuous horary observations on the declination at the times of the equinoxes and solstices, in conjunction with Arago and Reich, at Paris and in the mines of Freyburg respectively. The notion of a purely local origin of these storms, or disturbances, as they are usually termed, was soon dispelled by the fact that they would sometimes be felt simultaneously at each of the three stations, whilst at other times a disturbance at one of the stations would not be accompanied by a similar disturbance at the others. A magnetic expedition into Northern Asia, undertaken soon afterwards at the command of the Emperor of Russia, gave Humboldt the opportunity of laying his views before the Imperial Academy of Sciences at St. Petersburgh, who at once acceded to his request, and a chain of magnetic and meteorological stations was formed throughout the Russian empire, under the superintendence of Professor Kupffer. Such was the origin of the first Magnetic Association. The results obtained from the various affiliated stations were quite in accordance with the previous experiences of Humboldt, as showing the recurrence for each particular station of perturbations at the same hour, often for several days and nights in succession, whilst a comparison of distant stations showed, that with so much of general synchronism as precluded the idea of their being accidental or due to merely local causes, they nevertheless appeared to present special features depending on the place of observation.

The labours of this which we may call the Berlin Association were taken up and extended, in 1834, by one still more widely known, which, under the able direction of Gauss and Weber, had its centre of operations at Göttingen. The work so happily commenced by the older association was energetically carried on, and the methods of procedure were improved in

several important particulars. It had become evident that the instrumental means hitherto employed were inadequate to the accurate determination of the minute changes now under consideration, and in particular no means existed for detecting the variations in the intensity; and yet it was extremely improbable that this element should be unaffected by the irregularities which manifested themselves in the declination. The first improvement, which we owe to Gauss, was the introduction of a new class of instruments, capable of a precision hitherto supposed unattainable; whilst the bifilar magnetometer, also the invention of Gauss, rendered possible a corresponding record of the changes in the horizontal force. The number of term-days (i.e. set days for continuous observation at each of the associated stations) was at first six in the year, though afterwards reduced to four; and the interval between the observations was five-minutely instead of hourly. The term-days of the Association, which were limited to the observations of the declination only, commenced in 1834, and were kept regularly till 1841, when they were discontinued. Enough, however, had been done already to show that whilst previous results were fully confirmed, a still more extensive and complete organisation was necessary before we could hope to disentangle the manifold intricacies of the phenomena. That organisation was not long wanting. For some time, strange to say, England had taken no part in the labours of the Göttingen Association; but in 1836 the national interest was awakened by an appeal from Humboldt to H.R.H. the Duke of Sussex, who was then President of the Royal Society, and in 1837 the subject was formally brought before the British Association, at their meeting at Liverpool, by the masterly report of General Sabine, justly characterised by Humboldt as the most complete work of the kind. The author passed in review the observations already made, stating the conclusions to which they lead, and pointing out what still remained to be accomplished. The most important of the conclusions arrived at, and which, it must be remembered, were deduced mainly from observations in the Northern hemisphere, so far as the higher latitudes were concerned-may be summed up as follows::

(1.) The systematic non-parallelism of the lines of equal force and equal dip; these lines everywhere indicating the existence of two centres of unequal force, not situated on opposite meridians; i.e. not differing by 180° in longitude.

(2.) The unsymmetrical distribution of the intensity. If

the globe be divided into Eastern and Western hemispheres by a plane coinciding with the meridians of 100° and 280°, the Western hemisphere, or that containing the Americas and Pacific Ocean, has a much higher intensity generally distributed over its surface. than the Eastern, or that containing Europe, Africa, and the adjacent parts of the Atlantic Ocean.

(3.) The position of the maximum of intensity in the North American quarter does not coincide with that of maximum dip.

(4.) The arrangement of the lines of intensity in the Southern hemisphere seems, so far as observation has gone, to support the conclusions arrived at for the Northern hemisphere. Foremost among the matters which still awaited accomplishment were placed the complete survey of that part of Canada which was known to contain the maximum of intensity in the North American quarter, and the filling up of the void existing in the Southern hemisphere, particularly in the vicinity of the parts of this hemisphere which are of principal magnetic interest. This could only be done by a naval expedition, for ⚫ which it was natural that all countries should look to England." This report met with the warm approval of the Association, which body, in conjunction with the Royal Society, represented to Her Majesty's Government the desirability of a Southern magnetic survey, as well as the establishment of magnetic observatories in various parts of the British Empire, to take part in the Göttingen system of simultaneous observation. The result was the formation by the Government of magnetic observatories at Toronto, St. Helena, Cape of Good Hope, and Hobarton, and the despatch of the Antarctic expedition, consisting of the Erebus' and Terror,' the former of which was under the command of Capt. James Ross, and the latter under that of Commander Crozier. The expedition started in September 1839, and returned to England in 1843, having successfully accomplished what we have no hesitation in describing as the most extensive, most important, and most perilous survey ever undertaken. The observations extended over nearly two-thirds of the globe in the Antarctic regions, and were carried as far South as 74° 4′, further progress being prevented by difficulties absolutely insuperable. When the records of the expedition were examined, it was found that a portion of the Southern hemisphere, between the latitudes of 60° and 65° and longitudes 0° and 130°, was not included in the survey. To supply this hiatus the Pagoda was hired at

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