220 



NATURE 



[July 3, 1890 



trie forces, which is cited as a proof of Maxwell's theory 

 of stress in the medium, is rather an obstacle than a 

 support to the theory, as some dielectrics are strained in 

 one way, and others in the opposite, while, on Maxwell's 

 theory, the strain should all be of one kind. The state- 

 ment on p. 97, that the sparking distance increases very 

 much more rapidly than the increase in the difference of 

 potential between the electrodes, should have been limited 

 to the case where the electrodes are pointed ; it is not 

 true when the dimensions of the electrodes are large 

 compared with the sparking distance. The proof of the 

 expression for the electromotive force due to induction, 

 on p. 170, does not seem to us to be sound ; and the 

 method of measuring the coefficient of self-induction of 

 a coil was really invented by Maxwell, and given by him in 

 his paper on the " Dynamics of the Electric Field," though 

 it is not in the " Electricity and Magnetism." 



We must, in conclusion, congratulate the author on 

 having written one of the best treatises on elementary 

 physics which it has ever been our good fortune to read. 



J. J. T. 



THE ART OF PAPER-MAKING. 

 The Art of Paper-Making. By Alexander Watt. 



(London : Crosby Lockwood and Son, 1890.) 

 ' I ""HE author of this work, in the preface, expresses his 

 J- thanks to certain gentlemen who have been good 

 enough to conduct him through their mills and explain 

 to him the various operations performed therein. From 

 this we gather that the author is not only not a practical 

 paper-maker, but that, up to the time of writing the book, 

 he had but a limited and general knowledge of the sub- 

 ject. These conclusions are amply justified by a perusal 

 of the book. This want of practical knowledge can 

 hardly be wondered at, as the writer is already an 

 authority on such widely different subjects as soap- 

 making, leather manufacture, electro-metallurgy, electro- 

 deposition, &c. 



On the other hand, there is evidence that on the whole 

 the author has devoted some considerable time to the 

 reading up of his subject, though in many cases he has 

 not consulted the latest authorities. For example, in 

 speaking of the properties of cellulose, he quotes the 

 opinions expressed by Mr. Arnot in his Cantor Lectures 

 for 1877, since which time several additions have been 

 made to our knowledge. We should have preferred to 

 see more space devoted to this branch of the subject, as 

 on the proper understanding of the properties of cellulose 

 the scientific manufacture of paper depends. 



Some of the statements with regard to cellulose are 

 inaccurate and misleading, as for example, that " hydro- 

 chloric acid converts it into a fine powder without alter- 

 ing its composition," and again, that " nitric acid forms 

 substitution products of various degrees, according to the 

 strength of acid employed." As a matter of fact, ordinary 

 nitric acid does not form nitro-substitution products with 

 cellulose. 



Under the head of the " Recognition of Vegetable 



Fibres by the Microscope," esparto— perhaps the most 



important raw material used in this country — is not even 



mentioned. The author's descriptions of the various 



NO. 1079, VOL. 42] 



mechanical appliances used in paper-making are, with 

 one or two exceptions, accurate and fairly complete. In 

 describing the chemical processes involved, however, the 

 author occasionally gets out of his depth. For instance, 

 he recommends certain qualities of rags to be boiled with 

 30 per cent, of caustic soda. At first we thought this was 

 a misprint for 3 per cent., but on referring to the source 

 of the information, we found that the author had quoted 

 correctly. Again, we are told that the neutralization of 

 chlorine in pulp by hyposulphite, which the author says 

 is sometimes called thiosulph/te, is effected when the 

 liquor ceases to redden litmus paper. 



In giving directions for the sizing of paper, the author 

 appears to have left out a number of decimal points. 

 According to him 100 parts of pulp require 10-12 parts 

 of rosin, and 20-30 parts of starch, and from 30- 5a 

 parts of kaolin. In the interest of the consumer it is 

 satisfactory to know that such numbers are impossible. 



In the chapter containing directions for the testing of 

 alkalies, alum, &c., the following extraordinary statement 

 occurs : "There are two principal methods of analyzing 

 or assaying alkalies by means of the test acid — namely, 

 volumetric, or by volume, and gravimetric, or by weight, 

 in which a specific gravity bottle, capable of holding 

 exactly 1000 grains of distilled water, is used." 



Another instance of looseness of style occurs in the 

 statement that " the proportion of caustic soda per cwt. of 

 rags varies to the extent of from 5 to 10 per cent, of the 

 former to each cwt. of the latter." 



The general plan of the book also shows want of care- 

 ful preparation ; for example under the head of " Action 

 of Acids on Cellulose," the author discusses the action of 

 the strongly alkaline solution of cuprammonium. 



In speaking of the origin of the wood-pulp process, the 

 author champions the right of his father to be regarded 

 as the pioneer. Similarly, with regard to electrolytic 

 bleaching, we are told that the modern Hermite process, 

 which has been successfully applied to the bleaching of 

 paper pulp, is the outcome of an invention patented by 

 his brother in 1851. It is perfectly true that in this 

 patent the electrolysis of chlorides was claimed, but this 

 in no way diminishes the credit due to those who have 

 based on this principle a practical and successful manu- 

 facturing process. 



OUR BOOK SHELF. 



A Contribution to the Natural History of Scarlatina, 

 derived from Observations on the London Epidemic of 

 1887-88. By D. Astley Gresswell, M.A., M.D. Oxon. 

 (Oxford : Clarendon Press, 1 890.) 

 This volume constitutes Dr. Gresswell's dissertation for 

 the degree of Doctor of Medicine at Oxford, and is pub- 

 lished " as a mark of distinction " by the University. It 

 is the result of some six months clmical work at the 

 South-Western Fever Hospital of the Metropolitan 

 Asylums Board, and the author is to be congratulated 

 alike upon the large number of carefully recorded ob- 

 servations which he has made, and upon the evidence 

 his book affords of his careful study of the literature of 

 scarlatina. 



Between September 1887 and February 1888 Dr. Gress- 

 well had charge of Aearly 600 fever patients, and the 

 statistical tables with which his treatise abounds are thus 

 based on no inconsiderable number of cases. After some 



