May 1 8, 1882] 



NATURE 



55 



The second part is taken up with a visit to Lemuria, 

 thereby meaning Madagascar and the Mascarene Islands 

 of Bourbon and Mauritius. This visit was made in 1862. 

 The Seychelles were not visited. Some noteworthy details 

 are given of a visit to Madagascar. The home of the 

 Ouvirandra fenestrate is well described, and the account 

 of a Mauritius hurricane is true to the life. It is men- 

 tioned that in the hurricane of March 12, 1868, the iron 

 girders, 200 feet in length, and weighing over 300 tons, 

 were blown from the railway bridge over Grande Riviere, 

 when a force of 100 pounds to the square foot must have 

 been exerted by the wind down the ravine. 



In an appendix to the second part, there is a chapter on 

 the natural history of Madagascar, contributed by Mr. J. 

 G. Baker, F.R.S., of Kew. 



The third part of the volume describes a visit to Colum- 

 bia along with Capt. Pirn and Mr. John Collinson, for the 

 promotion of a transit railway route through Mosquitia 

 and Nicaragua. 



The volume will commend itself to the general reader, 

 and the scientific notices mentioned therein will be found 

 very generally interesting and correct. 



Modern Metrology. By Lowis D' A. Jackson. (London : 



Crosby Lockwood, 18S2.) 

 It is no easy task to give an account of the various 

 systems of weights and measures in use throughout the 

 world, to trace their origin, and to express their equi- 

 valents in English and French weight and measure, but 

 this the author has undertaken in one part of his book, 

 and has brought together much valuable and interesting 

 information. This work is so far a cambist or dictionary 

 of weights and measures, both the scientific and commer- 

 cial equivalents of all foreign units being given. It would 

 have been well, perhaps, if the author had stated for each 

 country the precise authority from which he obtained his 

 equivalent, as works of this kind should as far as possible 

 contain within themselves means for verifying the accu- 

 racy of the figures given. 



The main object of the work appears, however, to be 

 the discussion of a remedy for the evils of the complex 

 systems of weights and measures which are unfortu- 

 nately still in use in this country. To provide such a 

 remedy is a serious task, and one well worthy of the 

 attention of a great statesman such as Mr. Gladstone, to 

 whom this work is inscribed. 



The author discusses the vexed question of the relative 

 values of standard temperatures at 32° and at 62 , and 

 proposes a new English system based on a cubic foot of 

 1000 "fluid ounces," at the temperature of the maximum 

 density of distilled water. 



The "fluid ounce" is taken as equal to the weight of 

 distilled water contained in a cubical vessel whose dimen- 

 sions are equal to a "tithe," or tenth part of the linear 

 foot, when weighed and measured also at the temperature 

 of the maximum density of distilled water. The various 

 parts and multiples of the cubic-foot and " foot- weight " 

 would be built up by decimal progression, so that a strict 

 correspondence would be always maintained between 

 capacity, linear dimension, and weight. The effect of 

 reducing the temperature of the cubic foot from 62° F. 

 (the present legal temperature) to yf-\ F. (the temperature 

 of the maximum density of water), would bring the weight 

 of the cubic foot more into accordance with modern re- 

 search, as it would raise its weight from 62321 lb. to 

 62-424 lb. 



Although we have faint hope of present success in dis- 

 turbing the deeply-rooted systems of measures now in use 

 by this great commercial nation, or of substituting for 

 the purposes of international science a more acceptable 

 metrology than that based on the metre and gramme, we 

 cannot but recommend this work to the consideration of 

 all interested in the practical reform of our weights and 

 measures. 



LETTERS TO THE EDITOR 



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 No notice is taken of anonymous communications. 



[ The Editor urgently requests correspondents to keep their letters 

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 that it is impossible ot/n noise to ensure the appearance ezen 

 of communications containing interesting and nozel facts.] 



Sun-Spots and Magnetic Storms 



Some particulars of the remarkable double outburst of sun- 

 spots in the latter part of April and of tbe magnetic disturbances 

 which appear to have been connected « ith them, as recorded at 

 Greenwich, may be of interest to your readers. It is in itself a 

 noteworthy fact that there should be on the sun at the same time 

 two spots, one of them double, sufficiently large to be visible to 

 the naked eye, and this is made still more interesting by the 

 occurrence of a violent magnetic storm a few days after the 

 appearance of each of these large spots. 



The larger of the two spots would seem to have first made its 

 appearance at the east limb on April It at about 15I1 G.M.T., 

 though no photograph of it was obtained till April 14. It must 

 have passed off the disk about April 25 8h., being well shown on 

 a photograph on April 24. It extended over io° of heliographic 

 longitude, and measured more than 2' of arc in length and 

 breadth. 



The group preceding it, consisting of two spots, was first pho- 

 tographed near the east limb on April 1 1, and was then com- 

 paratively small. Between April 16 and 17 it increased suddenly 

 in size, becoming nearly as large as the other spot group, and 

 far exceeding in area any of the spots previously recorded at 

 Greenwich. 



The areas of these groups on the photographs, expressed n 

 million! hs of the sun's visible hemis| here, and correct :d for fore- 

 shoitening were as follows : — 



Preceding Gr.up. 



Nucleus. Whole Spct. 



17 ... 141 



40 ... 270 



24 ... 156 



204 ... S80 



244 ... 1370 



294 ... 1813 



440 ... 2360 



167 ... 1054 



April 1 1 



14 ■.. 35' 



16 ... 239 



17 - 391 



18 ... 465 



20 ... 340 



21 ... 427 



23 .. 267 



24 ... 316 



The total spotted area 



Great Spot 



Nucleus. Whole Spot. 



2218 

 2086 

 '979 

 2030 

 1916 

 2105 

 1786 

 1727 



1SS2, April 17, was 881 for the 

 nuclei, and 4668 for the whole -pots, being abjut double of the 

 greatest spotted area shown on any of the Greenwich photographs 

 previous to this outburst. 



On April 16 and 19 violent magnetic disturbances occurred. 

 At Greenwich the declination, horizontal force, and vertical 

 force magnets became violently disturbed on April 16 at Iih. 

 30m. G.M.T., the first movement for all three being simultaneous 

 and sudden, and the storm movements continued till April 17, 

 7h. 30m. G.M.T. The magnets remained quiet till April 19, 

 shortly after 15I1. 30m. G.M.T., when another sudden and 

 very sharp disturbance commenced, lasting till April 20, 

 20b. G.M.T. 



In the magnetic storm of April 16-17, there were lage oscil- 

 lations of declination till April 17 oh., the greatest recorded 

 motion being about i°, from a diminished declination at 19I1. + 

 to an increased declination at igjh. Then until 4I]. the register 

 cannot be traced, the motions being either unusually rapid, or 

 the magnet being disturbed by workmen in the upper room. 

 About 7I1. there were some sharp motions, after which time the 

 magnet became quiet. The principal feature of the disturbance 

 of horizontal force was at first an increase, followed by a much 

 larger diminution, amounting to about 1.50th of the whole force 

 at l6h., when tbe trace went off the sheet, and was lost until 

 April 17 oh. There was then a great and rapid increase (in 

 about 40m.) of about i-40th part. Rapid motions were 

 then shown till 7I1. 3cm. The whole range of these disturb- 

 ances probably exceeded I -25th part of the whole force. The 

 vertical force at first decreased somewhat till April 16, i6h.,and 

 afterwards very considerably till al« ut iSh., when it was din unshed 

 by about I- tooth part, then with the horizontal force it increased 

 till about lb., when the trace went off the sheet, its value being then 



