274 



NATURE 



[Jan. 22, i< 



we hope to analyse more particularly hereafter, when we 

 have the complete work before us. 



Two important suggestions present themselves to us, 

 as tending to render the book more useful. The 

 first of these it is now impossible to apply. We 

 think it would have been far better had the author 

 intercalated the diagnoses of those British species not 

 found in Dorsetshire amongst the descriptions of the 

 others ; this no doubt would have been done, but for the 

 original indecision in the plan of the work. It is not yet 

 too late to consider the other suggestion, viz., that a table 

 of the family and generic characters be given at the end 

 of the second volume. The expression at p. xxxvii. of 

 the introduction, to the effect that "the subject of classi- 

 fication being practically exemplified in each of the 

 ensuing descriptions, need not be further gone into here " 

 is not in keeping with the popular aims of the work, and 

 is not fair to those students who have not already ac- 

 quired a considerable amount of that knowledge possessed 

 by the author. 



The three plates are excellent, and in Mr. Cambridge's 

 usual analytical style. The work reflects great credit 

 upon the local Society that issues it, which deserves the 

 support and hearty thanks of all (we fear but few) who 

 are interested in British Spiders. 



Studies on Fermentation ; the Diseases of Beer, their 

 Causes, and the Means of Preventing them. By L. 

 Pasteur, Member of the Institute of France. A Trans- 

 lation, made with the author's sanction, of " Etudes 

 sur la Bicre," with Notes, Index, and original Illustra- 

 tions by Frank Faulkner and D. Constable Robb, B.A. 

 Oxon. (London : Macmillan and Co., 1879.) 

 We thoroughly agree with the following sentence from 

 the English edition of Pasteur's important work : "The 

 debt which English brewers owe to M. Pasteur can 

 hardly be over-estimated ; " but, further than this, we 

 believe that the debt which biologists of all countries owe 

 to him for his researches is also a very large one, for it is 

 by a study of these low and simple forms of life that they 

 may expect to learn something of the very beginnings of 

 life itself. 



On the appearance of the original work a very elaborate 

 notice of it appeared in these pages (Nature, vol. xix. p. 

 216) ; we need, therefore, now only call attention to this 

 excellent translation, which contains many notes supple- 

 menting the facts mentioned in the original edition, several 

 original illustrations, which cannot but be of great value 

 in the microscopical study of the changes in the liquids 

 with which the brewer has to deal, and an excellent index, 

 which immensely facilitates the using of the volume. 



This book may be, in the first place, one of special 

 interest to the practical brewer, but it has a nearly equal 

 interest for every careful student of nature, and it is so 

 clearly written, with all the technical expressions so well 

 explained, that we doubt not that the ordinary reader 

 who takes it up will not put it on the shelf again without 

 a perusal. The chapter on the physiological theory of 

 fermentation is one we would specially commend to the 

 general reader, to whom it may open up a quite new 

 field for thought. 



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 Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting and novel facts .] 



Ice-Crystals 



_ I DO not know whether any satisfactory explanation can be 



given of the different forms assumed by ice-crystals on the 



different substances on which they may be formed. These forms 

 are very various. During an intense frost some years ago I 

 observed upon the handrail of a wooden bridge a perfect forest 

 of ice-crystals very closely resembling the form of ferns, standing 

 upright, or rather at right angles with the surface from which 

 they sprang, with stems, midribs, and fronds, the only difference 

 being the prominence of rectangular arrangements. 



Everyone has seen the variety of forms assumed on window- 

 panes, where the crystals do not take erect positions as they did 

 in the case last mentioned, but lie flat upon the surface of the 

 glass. 



My object, however, now is to direct attention to another 

 form assumed by ice-crystals which is comparatively rare, and 

 which =eems to me to indicate the action of forces of a very 

 peculiar kind. 



When frost occurs suddenly as a change from a mild atmo- 

 sphere highly saturated with moisture (which is common in the 

 climate here), a peculiar form of ice-crystal is often formed upon 

 rotten branches lying on the ground under trees. This form is 

 that of long silky filaments, from two to three inches long, like 

 finely spun glass. These seem to effloresce from the rotten wood, 

 and form plumes of the most exquisite delicacy and whiteness, 

 often curling towards the ends, and lying over the branch from 

 which they spring. 



It is curious that this form of ice-crystal seems never to Jbe 

 attached to any rotten branch of which the bark is unbroken ; 

 but whenever the bark upon such branches has been split, 

 broken, or exfoliated, then from the exposed ligneous surface 

 in certain stages of decay, these lovely plumes of ice rise up, 

 pushing their way from underneath the projecting bits of bark, 

 then bending round them and curling over tbem. 



What is it in rotten woody fibre which determines this pecu- 

 liar form of the ice-crystal? The phenomenon seems to be due to 

 some special "lines of force" connected with this special mate- 

 rial under special conditions. 



During the last two nights we have had sharp frost succeeding 

 some very mild and very damp days. In the mornings it ap- 

 peared as hoar frost upon the grass, but during the whole day, 

 long after all hoar frost had disappeared, there were scattered, 

 under all the old woods, shining spots of snowy whiteness, and 

 on going up to these one found invariably that they were bits of 

 rotten branches, with exfoliated bark, and bearing these peculiar 

 plumes. 



If any of your contributors can give any scientific explanation 

 of this phenomenon, they would much oblige. ARGYLL 



Inverary, January 13 



Re-Reversal of Sodium Lines 

 The notice of the Proceedings of the National Academy of 

 Science in Nature, vol. xxi. p. 143, misrepresents, of course 

 unintentionally, certain remarks of mine upon "dark" spectrum 

 lines. I have not, and never have had, the slightest doubt that 

 the dark lines of the solar spectrum are true absorption lines. 

 The lines in question, which I am inclined to think may not be 

 due to absorption, are only those produced in certain peculiar 

 cases. If, for instance, a sodium flame be "urged," by in- 

 creasing the intensity of the flame and the quantity of metallic 

 vapour present, each of the two D-Iines becomes double, as is 

 well known, widening out and showing a dark stripe down the 

 centre. Hitherto this dark stripe has been universally ascribed 

 to the absorption produced by the envelope of colour-vapour 

 surrounding the flame. But if a lime-light be placed behind the 

 flame, then, as I have found by repeated experiment, this central 

 dark stripe re-reverses, and we have the sodium lines quadruple, 

 and dark upon a light ground. The experiment is rather delicate. 

 The bead of fused sodium bicarbonate in the flame of a Bunsen 

 burner is placed some two inches from the slit of a spectroscope 

 of sufficient dispersive power to separate the sodium lines about 

 a degree ; then the incandescent lime is set four or five inches 

 behind the flame, and so as to bring the edge of the shadow of 

 the bead just on the slit. 



Now it seems to me that this re-reversal shows that the dark 

 stripe which appeared before the lime-light was placed behind 

 the sodium flame, could not have been a mere absorption-line, 

 but must have been due to a real doubling of the line, the 

 substitution of two maxima of radiation for a single one ; I am 

 unable to see how, on the contrary supposition, the centre of the 

 line should have less absorptive power than the two pairs of lines 

 which show black when the lime is brought into action. 



May I mention in this connection a very pretty experiment 



