8o 



NATURE 



\_May 1 6, 187 



appeared to them to have at bottom no vahie. In their inmost 

 heart they always guarded the firm persuasion that liberty alone 

 is able to remedy the abuses of liberty, and that a more mature 

 science would rectify the errors of an incomplete science. The 

 sentiment which urged them to shake off the yoke of the Roman 

 Church is also that under the SMay of which the German 

 universities have been organised. 



But every institution founded on liberty is obliged to count on 

 the intelligence and judgment of those who use the liberty. In- 

 dependently of what has been said above on the subject of the 

 decisions which the students have to take for themselves in what 

 concerns the direction of their studies and the choice of their 

 masters, the reflections which precede show also the influence 

 which they may exercise on the masters themselves. It is a 

 difficult thing to have to continue the ccurse commenced by a 

 colleague, and that difficulty is presented at the outset of every 

 semester. At every moment the progress of the coune obliges 

 us to fall back upon what has been previously said, to consider 

 the same questions from other points of view and in another 

 order. The master would soon tire of this ungrateful task, if 

 he did not find support in the zeal of his audience. In order to 

 be at the height of his mission, he must feel himself sustained 

 and understood by a sufficient number of intelligent pupils. 

 The flocking of an audience to the lessons of a master has no 

 little influence on his nomination or his advancement ; and it has 

 an influence also upon the whole of the teaching body. All this 

 system rests upon the idea that the general current of the opinion 

 of the students cannot long be at fault. The majority among 

 them come to us with a reason sufficiently formed by logic, with 

 a sufficient habit of intellectual effort, with a judgment so con- 

 siderably developed by a knowledge of the best models, to be 

 able to discern the truth from a phraseology which has only the 

 appearance of truth. Among students we may already distin- 

 guish the elite ^^•ho will be the intellectual guides of the new 

 generation, and who, in a few years, may perhaps attract the 

 attention of the world. They are those who, especially, in 

 scientific matters, determine the opinion of their comrades ; 

 the others involuntarily allow themselves to be guided by them. 

 Naturally, young spirits, inexperienced and impressionable, are 

 liable to fall momentarily into error ; but, in short, we may be 

 sure that they will always return soon to just ideas. 



Such are, at least, those ^^ horn the ly-^eums have sent to us 

 hitherto. It would be dangerous for the universities to see 

 arriving in great numbers, students less cultivated. It is neces- 

 sary that the general spirit of the students should not decline. 

 If that happened, the dangers of academic liberty would sur- 

 pass its advantages. We ought not then to accuse the univer- 

 sities of pride or pedantry, when they admit only with circum- 

 spection students educated outside the lyceums. It would be 

 more dangerous still for a foreign pressure to introduce into the 

 faculties masters who would not be fully qualified for having the 

 scientific independence of an academic professor. 



Do not forget, then, dear comrades, that you have a great 

 responsibility. This glorious legacy of the past, of which I 

 have already spoken, you have to preserve, not only for our own 

 nation, but also to serve for example to a great portion of 

 humanity. You are bound also to prove that youth is capable 

 of enthusiasm for the independence of convictions and of 

 working for it. I say working. In fact, the independence of 

 convictions does not consist in lightly accepting hypotheses with- 

 out proofs; it can only be the fruit of experiments and of 

 persevering labours. It is your duty to show that the convic- 

 tions, founded on personal researches, are germs most fruitful of 

 new ideas, and furnish better rules of cond\ict than the direction 

 of the best-intentioned authority. Germany, who, in the 

 sixteenth century was the first to strive for the liberty of convic- 

 tions, who suffered and was martyred for them, is yet in the van 

 of the fight. A noble mission is allotted to her in the history of 

 the world, and you are called to contribute to its triumph. 



REMARKABLE CHANGES IN THE EARTH'S 

 MAGNETISM^ 



QNE of the most important, scientifically, of the special lec- 

 tures at the Geographical Society, was that by Capt. Evans, 

 m March last, on the subject of terrestrial magnetism. The 



' From Lecture at the Royal Gecgraphxal Society, March ii, by Captain 

 F J. Evans, C.B. F.R.S, Hydrcgrapher to the Admiralty. 



concluding portion, especially, is of high scientific importance, 

 Capt. Evans gave a historical sketch of the subject of terrestrial 

 magnetism from the time of the discovery of the dip of the 

 magnetic needle. After speaking further on various depart- 

 ments of his subject, Capt. Evans went on to say : — 



" We have now passed in review the successive stages of de- 

 velopment of our branch of knowledge, from the pregnant 

 epoch when its principles were enunciated by Gilbert, till the 

 period when the well-directed munificence of his own and other 

 Governments dotted the earth's surface with observatories, and 

 despatched land and sea expeditions, specially equipped, for the 

 determination of the magnetic elements. We have seen how a 

 few earnest and gifted men have, by long and patient analysis, 

 laid the foundations for future generations to build upon as re- 

 gards theory, and unravelled the apparently inextricable web 

 surrounding the needle's daily and yearly movements ; tracing 

 these movements to their primary source, the sun : and how by 

 the perseverance of states and of individuals, we are now in 

 possession of accurate knowledge as to the distribution of 

 magnetism over the surface of our globe, as represented by the 

 variation and dip of the needle, and by the measure of the force 

 connected with those component elements. But the task, from 

 a scientific point of view, is far from completed while we remain 

 in ignorance of the causes of greater changes in the earth's 

 magnetism going on from year to year, and so on, possibly.through 

 aeons of time. From a practical point of view, so far as the 

 interests of men are concerned, the collection of records will be 

 a never-ending task, for every generation must observe and chart 

 the magnetic elements of its time. 



"The subject of secular change is thus one of such great 

 interest that the remaining portion of my lecture must be chiefly 

 devoted to it. The active mind of Ilalley was drawn, as one of 

 the first, to the probable nature of the causes : collecting such 

 observations of the variation of the compass as had then been 

 made, and projecting them on polar maps, he found that the 

 convergence of the several directions of the needle led to two 

 points in each hemisphere. On this he enunciated the proposi- 

 tion ' that the whole globe of the earth is one great magnet, 

 having four magnetical poles or points of attraction ; near each 

 pole of the equator two ; and that in those parts of the world 

 which lie near adjacent to any of these magnetic poles the needle 

 is governed thereby, the nearest pole always being predominant 

 over the more remote.' Ilalley saw, as he confessed with 

 despair, the difficulties attending the proposition, *as never 

 having heard of a magnet having four poles,' but there were 

 the facts manifested by the earth, and he was too sagacious and 

 sound a philosopher to pass them by. He accordingly propounded 

 a theory which, however fantastic it may now appear, and 

 perhaps did at the time he wrote, has nevertheless within it the 

 fire of genius, and may probably be found yet to contain some 

 sparks of truth. To account for the four poles, and at the 

 same time for the secular change of the variation, he conceived 

 that the earth itself might be a shell, containing within a solid 

 globe, or terella, which rotated independently of the external 

 shell : each globe having its own magnetic axis passing through 

 the common centre ; but the two axes inclined to each other and 

 to that of the earth's diurnal rotation. It is not difficult to follow 

 the movements of the consequent four imaginary poles in solu- 

 tion of the problem. 



" Ilansteen working at the same problem a century after Halley 

 [181 1- 19], and much on the same lines, came nearly to the same 

 conclusion with regard to the four poles of attraction : and he 

 rendered justice to Halley by recognising him as the first who 

 had discovered the true magnetic attraction of the globe. Han- 

 steen, with the material at his command, went however a step 

 further, and computed both the geographical positions and the 

 probable period of the revolution of this dual system of poles 

 or points of attraction round the terrestrial pole. From these 

 computations he found that the North American point or pole 

 required 1,740 years to complete its grand circle round the 

 terrestrial pole, the Siberian 860 years; the pole in the Antarctic 

 regions south of Australia, 4,609 years ; and a secondary pole 

 near Cape Horn, 1,304 years.^ The influence of these laborious 

 investigations on the minds of subsequent inquirers may easily 

 be imagined. 



"The matured views of Sir Edward Sabine on the secular 

 changes — enunciated in the clearest manner in 1864-72 — are 

 deserving of the highest consideration. An ardent admirer of 



' Unieniichjingeii Tiber de7i Mag7i.etismus det Erde. Chrlst'ania,'i8ig. 



