June 15, 1876] 



NATURE 



147 



filling in the depressions and old valleys of the Mesozoic 

 and Palaeozoic rocks, and often containing valuable beds 

 of lignite resulting from the decay of the vegetation which 

 found a congenial soil and climate amongst the lakes and 

 lagoons of the period. 



Mr. Hutton considers that there was a " Glacier 

 period" during older Pliocene times, and another of less 

 importance just before the Pleistocene epoch. Both of 

 these are of earlier date than " The Glacial period " of the 

 northern hemisphere, and in the view of the author, as 

 well as of Dr. von Hochstetter and Dr. Haast,* were due 

 not to climatical influences extending over the southern 

 hemisphere and differing from those of the present day, 

 but solely to the greater elevation of the land in New Zea- 

 land at those periods, and the consequent extension of 

 snow and ice over a larger area than at present. 



In Mr. Hutton, "The Theory of the Glacial Origin of 

 Lakes," at least as far as it applies to the province of 

 Otago, finds a new and welcome advocate; and his 

 observations on this question are opportune at this time, 

 as Prof. Ramsay's theory has been challenged by an able 

 writer in the pages of the Geological Magazine} Mr. 

 Hutton first examines the views of those who have re- 

 ferred the origin of these lakes in Otago to subsidences? 

 or terrestrial movements, and considering them inade- 

 quate, falls back on that of glacial erosion, in support of 

 which he can appeal to the evidence of former glacial 

 action along the shores of the lakes themselves. 



The latter portion of the volume before us is taken up 

 with the report of Mr. Ulrich upon the gold-fields of 

 Otago, which is of much local interest, and will doubtless 

 prove of value in guiding future adventurers, but does 

 not appear to call for special observation in a short 

 review. 



OUR BOOKSHELF 



Elementary Algebra, with Numerous Exercises, for Use 

 in Higher and Middle- class Schools. By David Munn, 

 F.R.S.E, (Collins' School Series, 1876.) 



The chief justification, perhaps, for the production of 

 this work is that the exigencies of a " school series " 

 demanded the publication of an elementary algebra. 

 There is not much more in it than is to be found in a 

 half-dozen similar works, and the explanations of rules 

 seem to us to fall short of those given elsewhere. We 

 do not like the frequent use oi evidently in an elementary 

 work ; our own extended experience with English school- 

 boys is that these elementary details are by no means 

 evident to the ordinary schoolboy mind. On p. 70 " the 

 L.C.M. of d"b'C and aH^c^ will evidently be d-^b'^c'-^" is evi- 

 dently wrong, for it evidently ought to be d^/?^c^. Art. 8 

 on p. 45 (to show that when a certain algebraical polyno- 

 mial is divided by {x — a), the remainder is what the 

 polynomial becomes when in it x is changed to a) is 

 useful, and we teach it to advanced pupils, but we are 

 disposed to think that few beginners could grasp the 

 truth and apply it. On pp. 173 to 176 we have some 

 interesting Miscellaneous Propositions on the progressions 

 which we do not remember to have seen in previous text- 

 books. The most important mistakes we have found are 

 on pp. 66, 96, 107, 151, 153. Here we may remark that 

 there is a very plentiful crop of typographical blunders ; 

 many of these we are disposed to attribute to a hasty 



' See Hochstetter's " New Zealand," English translaiion, p. 504. 

 ' No. 139, January 1867. The statements of Mr. Judd have called forth 

 several rejoinders in the ensuing number of the Magazine for February. 



examination of the "proofs;" frequent instances, too, 

 occur in which 2, 3, or 5 have got interchanged. There 

 is a large collection of exercises, but happily no answers 

 are given at the end, or the list of errata would doubt- 

 less have been greatly enlarged. From the fact that 

 (<2»«)« = (rt«)'» for positive integers, "it follows that 



{aq)'} =aPy This, we think, will hardly be admitted; 

 we should prefer to assume that the result holds, 



P 

 and thence derive an interpretation of aq . The book 

 takes in Indeterminate Equations, Permutations, Ratio, 

 Proportion, Variation, and the Binomial Theorem, The 

 only Scoticism we have noticed is one that frequently 

 occurs : it is, " we will find," &c. 



LETTERS TO THE EDITOR 



\The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. '\ 



The Early History of Magnetism 



Permit me to supplement "K.'s" excellent sketch of the 

 " History of Magnetism " (Naturf, vol. xiii. p. 523) by two 

 notices of the "Mariner's Compass," which seem to beef earlier 

 date than any hitherto found in Europe. They possess particular 

 interest from showing the compass in so rude a state as to lead 

 to the inference that we owe it to a re-discovery rather than to 

 an importation from China. The author of the notices is 

 Alexander Neckam, an English writer of the twelfth century, 

 and they are now included in a book which was privately printed 

 in 1857, entitled "A Volume of Vocabularies," illustrating the 

 condition and manners of our forefathers from the tenth to the 

 fifteenth century, edited from MSS. in public and private collec- 

 tions, by Thomas Wright, M.A., F.S.A., Hon. M.R.S.L., &c. 

 It was through the zeal and the liberality of Joseph Mayer, 

 F.R. A.S., F.S.A., of Bebington, that thesenotices were brought to 

 light, and a most useful volume was produced, of which he bore 

 the charge. 



As the discovery was made by Mr, Wright, it shall be reported 

 in his own words. In referring to the many points of interest 

 upon which new light is thrown by the vocabularies, he says : — 



"None of these, perhaps, is cf more importance than the 

 curious early allusion to the use of the mariner's compass by the 

 navigators of the western seas. It is well known to all readers 

 that this invaluable invention has been formerly supposed to 

 have been brought from the East, and not to have been known 

 in the West until the fourteenth century, when it was used by 

 the Italian mariners. Allusions to it have, however, been dis- 

 coveie 1 by the students of medireval literature in works which 

 date as far back as the thirteenth century. In the following 

 pages we find this invention not only alluded to in the twelith 

 century, but described in such a manner as to show that it was 

 then absolutely in its infancy, and to leave little doubt of its 

 having originated in the West, Alexander Neckam, in his 

 tieatise ' De Utensilibus,' enumerates among the ship's stores 

 a needle which was placed on a pivot, and when turned round 

 and left to take its own position in repose, taught the sailors 

 their way when the polar star was concealed from them by 

 clouds or tempest. I have discovered and printed in the note to 

 this passage, a passage in another of Neckam's works, the in- 

 edited treatise ' De Naturis Rerum,' which gives a more distinct 

 account of this invention. ' Mariners at sea,' he says, ' when 

 through cloudy weather in the day which hides the sun, or 

 through the darkness of the night, they lose the knowledge of 

 the quarter of the world to which they are sailing, touch a needle 

 with the magnet, which will turn round till, on its motion ceasing, 

 its point will be directed towards the north.' A comparison of these 

 two passages seems to show pretty clearly that at this time the 

 navigators had no regular box for the compass, but that they 

 merely carried with them a needle which had been touched with 

 the magnet (perhaps sometimes they carried the magnet also, 

 and touched the needle for the occasion), and that when they 

 had to use it they merely placed it upon some point, or pivot, 

 on which it could turn with tolerable freedom, and then gave it 

 a motion, and waited until it ceased moving. This mode of 



