June i6, 1898] 



NATURE 



47 



first of these is on Margot's method of coating glass 

 with aluminium and of soldering aluminium, or even 

 glass, by means of its aluminium coat 1 Prof. Threlfall j 

 vouches for the practical ease and success of these pro- 

 cesses. He gives full details of the very simple process. 



The second is on Boettgers process of depositing 

 bright gold upon glass, just as silver is deposited. This 

 also the authpr has proved to be satisfactory. The 

 question arises whether it might not be worth while, where 

 colour is not important, to use gold in the place of silver 

 in reflecting telescopes for the sake of the permanence 

 that should in this way be attainable. 



The third is on slitting with a disc and diamond dust 

 and making rock sections generally. This, however, does 

 not require particular notice except, perhaps, the curious 

 statement that the author was surprised how difficult it 

 was to learn anything about this art. Vol. iii. of 

 Holtzapffel surely cannot have been in his mind when 

 he wrote this. 



A large amount of space is given to the fullest details 

 of the different methods of making and mounting quartz 

 fibres and of their properties. No one with this before 

 him need have any doubt about embarking upon this 

 laboratory art. The writer of this notice had produced 

 the first of some articles on the subject in the Elec- 

 trician, but on seeing Prof. Threlfall's book, felt that 

 the ground was so well and accurately covered that 

 it would be a mistake to go over it again. The curious 

 property of the quartz fibre discovered by Prof. Threlfall, 

 of becoming at ordinary temperatures very slightly more 

 rigid as the temperature rises, is referred to ; and the 

 suggestion which the writer of this notice also put forward 

 tentatively years ago is made, that chronometer balance- 

 springs made of fused quartz might have some advantage. 

 This curious rise in rigidity with temperature is also 

 noticed by Mr. S. J. Barnett in a valuable paper in the 

 Physical Review for February last. Another point 

 referred to by both these writers is the extraordinarily 

 small coefficient of expansion of melted quartz. Benoit 

 gives the extreme coefficients for crystalline quartz as 

 •072 and "0*133. Barnett found for three quartz fibres 

 •o*'3, and for a rod of fused quartz •o''2. There is 

 one part of the description of the manipulation with 

 quartz fibres where the writer would add to Prof. Threl- 

 fall's description. On p. 220 the method of handling the 

 fibre, cutting it off, and mounting it so as to be of the 

 right length is described. Instead of a board to work 

 on, however black it may be, a piece of looking-glass 

 lying flat on the table is infinitely superior. This was 

 suggested years ago by some kind friend, but who it was 

 the writer is ungrateful enough not to remember. 



The writer prefers when blowing quartz fibres of 

 extreme tenuity for suspension purposes, not to blow a 

 maze on to some screen, but, using a finer flame, to blow 

 out a single fibre which may often be found joining the 

 two rods, and either thick enough to show colour or 

 generally far too fine to do so, corresponding in fact to 

 the black of the soap-bubble. 



Soldering, brazing, silver soldering, all essential every- 

 day arts, are next described well and fully ; but 

 whether these descriptions will make these actually easy 

 arts ever seem so to beginners is a question. Perhaps 

 enough is not made of the sweating process carried out 

 NO. 1494, VOL. 58] 



without any bit, or any preliminary cleaning or preparation 

 of any kind. On the other hand, under brazing and 

 silver soldering, the great use of a bit made of clean 

 iron wire in showing the melted metal where to go when 

 it does not flash at once, might be added in a future 

 edition. 



Insulators and conductors used in the construction of 

 apparatus are next considered. Prof. Threlfall is probably 

 the only person who has turned to useful account the 

 writer's discovery of the superlative insulating properties 

 of rods of melted quartz, even in an atmosphere saturated 

 with water. Their application to a number of electrical 

 appliances is described and figured. 



Glass, ebonite, mica, micanite, celluloid, paper, paraffin, 

 wood, slate, and marble are all discussed from the point 

 of view of a constructional material with insulating 

 properties. The electrical and mechanical properties of 

 a large number of alloys, such as platinoid, manganin, 

 &c., close this long and most valuable chapter. 



The last chapter is upon electro-plating, chiefly gold, 

 silver, copper and nickel, and upon allied arts. The writer 

 has often heard that the best nickel plating is really 

 cobalt. He hoped to, but did not, find any enlightenment 

 upon this point. 



An appendix upon platinising glass concludes the book. 



This notice, already too prolonged, and yet insufficient, 

 is enough to show that the experimentalist has now a 

 most useful guide in a large number of processes. It is 

 not possible to describe every process. The personal 

 certificate is what gives value to those that are chosen. 

 It is to be hoped that with Prof. Threlfall's valuable 

 guide, instead of despising them, some of our growing 

 physicists may be encouraged to make themselves familiar 

 with some, at any rate, of those arts which Newton and 

 Faraday cultivated with such astonishing skill and 

 success. C. V. Boys. 



A NEW TEXT-BOOK OF ZOOLOGY. 

 A Studenfs Text-Book of Zoology. By Adam Sedg- 

 wick, M.A., F.R.S. Vol. i. Pp. 600. (London : Swan 

 Sonnenschein and Co., Ltd., 1898.) 



MR. SEDGWICK has produced the first part of 

 what must prove to be a very useful treatise for 

 University students, if the remaining portions of the 

 work are as well carried out as is the present. . 



In this volume Mr. Sedgwick gives an account of 

 the Protozoa, Porifera, Coelentera, Platyhelminthes, 

 Nemertea, Nemathelminthes, Rotifera, Mollusca, An- 

 nelida, Sipunculoidea, Priapuloidea, Phoronidea, Polyzoa, 

 Brachiopoda, and Chaitognatha. The method adopted 

 is strictly systematic : the larger groups are described 

 and characterised in turn, the enumeration extending 

 as far as families, which are also briefly characterised, 

 important illustrative genera being cited. The work is, 

 in fact, written on the lines of the translation of the 

 "Zoology" of Prof. Claus, which Mr. Sedgwick gave us 

 some years ago ; but instead of merely producing a new 

 edition of that work, he has written a new book intro- 

 ducing his own views and his own conception as to what 

 are important facts and useful schemes of classification. 



A distinctive feature of the work is the number of ex- 

 cellent woodcuts which Mr. Sedgwick has culled from 



