158 



NATURE 



[December i6, 1897 



one kind, o'3i2 and 0'3i3 for the other. A further determina- 

 tion gives 0'304 for the first kind ; hence, generally, k lies be- 

 tween 0*30 and 0"3i. Noticing that certain kinds of ice are 

 anistropic, the properties being different along the vertical and 

 horizontal directions referred to the position when frozen, Signor 

 Straneo, in a subsequent paper, investigates the question as to 

 whether the thermal conductivity varies with the direction. In 

 homogeneous amorphous ice the values for the vertical and 

 horizontal directions were found to be practically equal (0*312 

 and 0'3o8), but homogeneous non-amorphous ice gave for the 

 same directions 0'328 and 0'30i respectively in one experiment, 

 and 0"325 and 0*308 in another, showing that only ice which is 

 not perfectly amorphous presents small differences in the co- 

 efficient of conductivity in different directions. 



The physical aspect of the reversal of the photographic 

 image is the subject of a suggestive paper by Captain Abney in 

 the Journal of the Camera Club. To investigate the matter, a 

 series of photo-micrographs of sections of films which had been 

 given known exposures was taken. From these sections it is 

 seen that the part of the films in which reversal has taken place 

 are markedly different at the upper and lower surfaces. Near 

 the upper surface the section shows comparatively fine grains of 

 silver, whilst at the bottom surface it shows coarser grains. At 

 the top part of the film, where the light has acted strongly, the 

 reversal has taken place. At the bottom the light has not acted 

 much more than usual, owing to the shielding action of the top 

 part. When given areas of the film are examined, the numbers 

 of separate silver particles are found to be very much the same 

 in both cases, showing that there is a sort of normal number 

 per volume which is subject to reduction, and that the main 

 difference is in the size of the reduced particles. In the course 

 of a discussion upon the subject of the paper. Dr. Armstrong, 

 referring to the sections of the unreversed image, considered 

 that Captain Abney had shown that to be the case which must 

 be the case, and that so long as there was no reversal the 

 particles must be practically as large as the bromide particles, 

 and all of the same dimensions. By showing that the particles 

 in the reversed image were so very much smaller, Captain Abney 

 had contributed in an important degree to the solution of the 

 character of the change that took place ; it appeared to him 

 that it had been shown that there was in some way a re- 

 conversion of the surface of the particle into soluble matter — 

 that evidence had been adduced to prove that there must be a 

 re-transference of the bromine back into the silver at the 

 surface, leaving untouched the silver lower down in the particle, 

 and consequently that when the fixing solution was applied, 

 the particle became reduced in size. 



An article of perhaps no little interest to many persons in 

 this country, and of some substantial importance to Spanish 

 industries, is the so-called gut from silkworms. This is useful 

 for fishing purposes, partly on account of its great tenacity and 

 partly owing to its transparent quality, the line attaching the 

 hook when in the water not being visible. The manner of 

 obtaining this threadlike gut is described in the Journal of the 

 Society of Arts as follows : — After the grub has eaten enough 

 mulberry leaves and before it begins to spin, which is during the 

 months of May and June, it is thrown into vinegar for several 

 hours. The insect is killed, and the substance which the grub, 

 if alive, would have spun into a cocoon, is forcibly drawn out 

 from the dead body into a much thicker and shorter silken thread. 

 Two thick threads (from each grub) are placed for about four 

 hours in clear cold water, after which they are dipped for ten or 

 fifteen minutes in a solution of some caustic, for which purpose 

 soft soap dissolved in water is used. This serves to loosen a 

 fine outer skin, which is next removed by the hands while the 

 workman holds the thread between his teeth. The silk is then 



NO. 1468, VOL. 57] 



hung up to dry, care being taken to choose a shady place, as the 

 sun has the effect of making them too brittle afterwards. In 

 some parts of the country these silk guts are bleached with 

 sulphur vapour, which makes them look beautifully glossy and 

 snow-white, like spun glass, while those naturally dried retain 

 always a yellowish tint. 



The current number of the Annali d^Igiene Speriinentale 

 contains a note by Dr. Casagrandi on a yeast producing a red 

 pigment which, in many respects, resembles the one described 

 by Damme some years ago, and isolated by him from a cheese. 

 Demme stated that his variety was not endowed with any 

 fermentative properties ; that isolated by Casagrandi, on the con- 

 trary, ferments glucose very readily. This fermentative power 

 is not, however, a trustworthy one for establishing differences 

 between very similar varieties of bacteria, for, as in other cases 

 so in this, Casagrandi has found that Demme's yeast can be in- 

 duced to ferment glucose if particular precautions are adopted. 

 Both Damme's and Casagrandi's sp^cim^n3 are pathogenic to 

 guinea-pigs, rabbits and rats, when subcutaneously introduced 

 'nto these animals ; whilst of much interest is the fact that when 

 grown in milk they are both capable of so modifying the character 

 of this liquid that dogs and rabbits fed with such milk develop 

 diarrhoea, and the same symptoms have been observed in babies 

 which had partaken of milk in which this red yeast had been 

 growing. This yeast appears to be present in our surroundings, 

 and may, therefore, at any time make its presence felt by obtain- 

 ing access to milk if the latter is left unduly exposed. We 

 already have one well-recognised red yeast, the so-called liosa 

 hefe, but Casagrandi doss not claim that his variety is anything 

 more than an offshoot from the second red yeast, known to us 

 as the Saccharomyces ruber discovered by Demme some seven 

 years ago. 



No. II, vol. iii., of Spelunca contains, among much other 

 cavern-lore, an illustrated account of M. Martel's explorations 

 in the British Isles in 1895. 



In the November number of the Irish Naturalist, Mr. G. H. 

 Kinahan urges the importance of a careful study of quartz-rocks, 

 when not metamorphosed, with a view to the recognition of 

 structures that may prove some of them to be of organic origin, 

 like the modern sinter produced by the algoe of hot springs. 



Mr. W. Jerome Harrison has reprinted, from the 

 Glacialists' Magazine, " A Bibliography of Norfolk Glaciology," 

 on the lines of his similar work on the Midlands. Over four 

 hundred papers are catalogued, in approximate order of publi- 

 cation, and short abstracts of the most important are given. 

 There is also a list of the Geological Survey maps, and an 

 author-index. A reproduction of a photograph of one of the 

 great chalk-masses in the drift of Runton forms a frontispiece to 

 this useful reprint. 



To commemorate the incorporation of the University College 

 of Sheffield, a number of scientific papers by members of the 

 College have been brought together and printed in a volume for 

 private distribution. The subjects of physical papers included 

 in the volume are : — The influence of carbon on iron, by Prof. 

 J. O. Arnold; the preparation of pure iron by electrolysis, by 

 Prof. W. M. Hicks, F.R.S., and Mr. L. T. O'Shea ; vortex 

 aggregates with gyrostatic quality, by Prof. Hicks ; functions 

 connected with tesseral harmonics, by Prof. A. H. Leahy ; super- 

 heated steam-engine trials, by Prof. W. Ripper ; the amount of 

 carbonic anhydride in the atmosphere, by Prof. W. Carleton 

 Williams ; and contributions to the knowledge of the Triazole 

 series, by Dr. George Young. In biological science there are 

 papers on the comparative intellectual value of the anterior and 

 posterior cerebral lobes, by Dr. C. Clapham ; the development 

 of the ovipositor in Periplaneta orientalis, by Prof. A. Denny ; 



