;i8 



NA TURE 



[August 2. 1694 



monary complaints. Tourists who like to leave the 

 beaten' track, and seekers after a refuge from an English 

 winter, will be attracted to Biskra if they read Mr. 

 Pease's little book. 



Practical Photo-Micrography. By Andrew Pringle. 



(London : Iliffe and Son, 1S94.) 

 Workers in this fascinating branch of science will no 

 doubt be well acquainted with the author's large treatise, 

 a book which is suitable, more especially, for those who 

 wish to devote themselves very considerably to this kind 

 of work, and to enter into all the details connected with 

 it. The publication of the present book will not appeal 

 so much to the interest of this class of readers, but will 

 be welcomed more by those who wish to get a good 

 working idea of photo-micrography. With this intention 

 this manual has been kept within very reasonable limits, 

 is decidedly explicit, and thoroughly practical. In the 

 seventeen chapters the reader is led through all the 

 manipulations, from the choice of instruments to suit 

 his purse, kinds of plates to use, colour treatment of 

 objects, and general photographic procedure, Sec, to 

 those dealing with good hints on lantern-slides, cover- 

 glass preparations, and section cutting and staining. 

 The text is accompanied with numerous well-chosen 

 illustrations, and the get-up of the book is all that could 

 be desired. It may interest our readers to know that in 

 the above pages we are informed that no apparatus is 

 recommended on hearsay, or is any statement made or 

 step suggested "outside the knowledge and practice of 

 the writer." 



Twelve Charts of the Tidal Streams on the West Coast 

 of Scotland. By F. Howard Collins. Small folio. 

 (London: J. D. Potter, 1S94.) 

 Mr. Collins has elaborated the work of the Hydro- 

 graphic Office by producing a set of charts showing the 

 direction of the tidal streams on the west coast of Scot- 

 land at intervals of one hour from the time of high water 

 at Greenock. The twelve charts arc prefaced by a note 

 describing how they should be used, and a tide-table. 

 The sources of his information are duly acknowledged, 

 and the work was carried out with the assistance of 

 Captain Wharton, the hydrographer. The work is 

 similar in scope and method to the atlas of tides in the 

 North Sea by the same author. It is a serious defect 

 that no method has been adopted for distinguishing the 

 velocity of the tidal streams, or at least of indicating the 

 furious tidal races which occur in many channels and off 

 many headlands. So far as the direction of the streams 

 is concerned, this compact set of charts should be 

 useful to yachtsmen, and is not without interest for 

 oceanographers. 



LETTERS TO THE EDITOR. 



[7ke BJi/or doti not hold himtelj responsible for opinions tx- 

 frtsttd by his correspondents. Neither can he underlaie 

 to return, or to correspond -.vith the writers oj, rejected 

 minuicripts intended for this or any other part o/"NatuRK. 

 No notice is taken of anonymous communications. ] 



On Some Methods in Meteorology. 



Is it not a desideratum in our rainfall records that ihey should 

 give, with the amount of rain, not mere rain day.? (or days' rain), 

 but the exact time (or as near an approximation to that as 

 possible), during which rain has fallen? This might at Icist, 

 lureljr, be expected from our observatories and better equipped 

 ^omc of our continental neighbours are before us in 

 Thus, the Geneva record, for more than thirty 

 )- , -jntained at one of its items, " hours of rain. " .May 



we not then ask why an institution like that at Greenwich, goes 

 on giving the number of days on which rain fell ; a momentary 

 sprinkle being thus put in the same category with an incessant 

 dowapour of twenty -four hours? 



NO. 1292, VOL. .so] 



One might here remark on the great fulness of detail and 

 excellence of arrangement in records of the weather at various 

 continental stations (e.g. Pola) ; which are apt to lead us into' 

 invidious comparisons. 



With regard to measurement of bright sunshine, the burning- 

 glass method leaves much to be desired from a scientific point of 

 view, and the photographic method seems likely to supplant it 

 increasingly. But might not the concentrated r.ays be got to 

 produce some other physical effect (metal-expansion ?) thai» 

 burning paper, yielding a more exact record of the amount of 

 sunshine ? 



.\gain, may it not be said that the graphic method is far too 

 little utilised in meteorology ? Prob,ably nine persons out often 

 would agree that they apprehend a truth of statislical nature, a 

 numerical variation, much belter every way — more quickly, 

 more clearly, more retentively — through a gr.iphic curve, than 

 through a column of figures, or a verbal description. Yet we 

 have only to turn over the p.ages of our meteorological publica- 

 tions (and others dealing with figures) to see that this method 

 is used very sparingly. .\nd it is easy to pick out cases where 

 the want of it is felt very plainly. I can recall one such case 

 in a valuable paper by one of our able-t meteorologists ^Dr. 

 Huchan), published a short time ago in the .Scottish Society's 

 Journal, on mean temper.iture in the neighbourhood of London 

 during 130 ye.trs. Here we find paragraph after paragraph, 

 over several pages, describing how certain smoothed v,alues of 

 temperature had varied, now above, now below the line of 

 average. This imposes a considerable strain on the imagina- 

 tion, proves, 1 am afraid, somewhat tedious reading, and leaves, 

 perhaps, no very distinct impression after all. .\ simple dia- 

 gram, giving the curves themselves, would here be an ertective 

 labour-saving contrivance, both to the author and his readers. 



But to multiply diagrams means great expense, it will natur- 

 ally be urged. Now the cost of a well-finished diagram (and 

 we all like such) is no douht considerable. But with the aid 

 of photography diagrams can now be reproduced very cheaply; 

 and it seems to me oprn to consideration whether we might not 

 do well to sacrifice a little fineness and finish, for the sake of 

 a freer and more frequent use of the method, and the greater 

 clearness of comprehension which th.at would ensure. More- 

 over, such diagrams are not to be regarded as a mere addition, 

 and therefore requiring more space ; they may even mean an 

 economy of words and space. There are frequent cases \a 

 which it is not necessary to give all the figures involved ; the 

 object being merely to point out a relation, the salient features 

 of a curve. And if ihe diagram can be relied upon for accuracy, 

 little need be said about it, in some cases ; it tells its own tale. 

 Then again, the photographic reproduction of an author's dia- 

 gram may even prove a gain in accuracy ; some intermediate 

 perils are avoided. I believe, in fine, that the graphic method 

 has a great future before it, not only in science, but in other 

 domains ; and thesooner we set about developing its capabilities 

 to the utmost, the belter. .\. I!. M. 



Magnetism of Rock Pinnacles. 



It is well known that the RilTelhorn powerfully affects the 

 comp.ass, and the like has been observed on other peaks in 

 Switzerland ; but I have never seen any record of similar obser- 

 vations in this country. 



Kour years ago, on a visit to the Lizard, accident drew at- 

 tention to a strong influence on the compass exhibited by a crag 

 on the moors near Kynance. I have taken the opporuinity of 

 a visit this year to ascertain whether that were a solitary case. 

 I find that such influence, though not general, is by no means 

 uncommon. Most of the rocks in which it was observed were 

 serpentine ; it occurred also in hornblende schist ; there were 

 no sulhcient opportunities of testing the other rocks of the 

 district. The influence was exhibited only in rather prominent 

 crags, but among them often in lower .adjacent blocks, as well 

 as ill the absolute summits. At a few yards' distance it was 

 always imperceptible. 



I saw no Ir.aces in any case of the crag having been struck by 

 lightning. This was the only point to which I gave attention ; 

 but it would be natural also to inquire if all kinds of rock can 

 possess the properly, if wet or weather affects it, and if it be 

 temporary or permanent. 



I used a common pocket compass, taking the bearings of some 

 distant object, first a few feet off, then in four surrounding 

 positions as near as the compass could be held to the stone I 



