556 



NA TURE 



[April 13, 189; 



In the third chapter some tests of the quality of milk 

 are discussed. The value of milk is gauged by the per- 

 centage of butter-fat, and although there are many 

 methods of estimating this, most of those which are 

 trustworthy are troublesome to work. Prof- Muir does 

 not speak well of the lactobutyrometer— an instrument 

 designed for the separation and direct reading of 

 the fat. The method is certainly rough, and almost 

 useless, except in the hands of a very careful worker. 

 There are two methods, not described by Prof. Muir, 

 which are of much greater value and not more trouble- 

 some ; these are the Babcock milk test and Soxlet's 

 method of estimating fat in milk from a determination of 

 the specific gravity of an ether extract. 



In speaking of cream separation on p. 45, Prof. Muir 

 mentions that " some kinds of separator have an arrange- 

 ment for regulating the thickness of the cream," and also 

 " that frequently separated cream is rather frothy." A 

 fuller treatment of these points would have been useful 

 The methods of regulating thickness of cream from a 

 separator depend upon varying the rate of revolution of 

 the separator bowl, or else upon varying the time the milk 

 remains in the bowl. The latter plan is most convenient, 

 and is usually effected by diminishing the inflow of milk 

 In the Danish separator the same end may be secured 

 by adjusting the movable skimming tube. Frothiness of- 

 cream is most marked in the case of the Danish machine 

 when the cream is taken off thick. This frothiness might 

 possibly be remedied by using a smaller nozzle for the 

 cream delivery tube. 



In dealing with the principles of cheesemaking on 

 p. 69, the author says, " The state of the milk with regard 

 to acidity is of the greatest importance just when the 

 rennet is added, and should it then be too acid little can 

 afterwards be done to counteract the mistake. On the 

 other hand, should the amount of acid be slightly too 

 little, it may be counteracted to some extent in the subse- 

 quent processes." 



As a matter of fact even the most skilful workers some- 

 times find the milk too ripe, and in such cases, by hasten- 

 ing the curd into the curd-sink and then washing with 

 water at 100' F., good results may be obtained, at least 

 by the " stirred-curd process." 



The book concludes with a short appendix on cream- 

 raising trials, made at the Yorkshire College. 



Prof. Muir's manual, though small, is to be welcomed 

 as a most useful addition to our dairy literature. 



Walter Thorp. 



OUR BOOK SHELF. 



William Gilbert of Colchester^ Physician of Londo7i, on 

 the Loadstone and Magnetic Bodies, and on the Great 

 Magnet the Earth. A New Physiology, Demonsti ated 

 with Many Arguments and Experiments. A Trans- 

 lation, by P. Fleury Mottelay. (London: B. Quaritch, 

 1893O . 

 Among men of science there is no difference of opinion 

 as to the value of the original Latin work, *' De Magnete," 

 of which this is a translation. Some time ago (Nature, 

 vol. xlii. p. 279) we gave an account of a meeting held at 

 Colchester by members of the Essex Field Club and the 

 Gilbert Club, for the purpose of doing honour to the 

 memory of Gilbert, who was born there in 1540. In a 

 speech delivered at this festival Lord Rayleigh not only 



NO. 1224. VOL. 47] 



spoke highly of Gilbert's work, but went on to say that 

 although we owe to an investigator who lived so long ago- 

 the theory that the earth is a great magnet, we are not much 

 in advance of that position at the present time, as nobody 

 has yet explained the origin of terrestrial magnetism. It 

 was most desirable that a work which may be said to 

 have marked a definite stage in the evolution of physical 

 science should be presented in an English form, and this 

 has now been done by an American scholar, who, as he 

 himself explains, has " translated with latitude, keeping 

 in view the author's sense more particularly than his 

 words, and amplifying without altering the former." Mr. 

 Mottelay has also brought together in a short biographi- 

 cal memoir the leading facts relating to Gilbert's career. 

 The volume is well printed on good paper, and will be 

 very welcome to students of the history of scientific 

 ideas. 



Report on Manurial Trials. By Dr. William 



Somerville. (Newcastle: Ward, 1893.) 

 This pamphlet, extending to 61 pages, gives the results of 

 manurial trials in the county of Northumberland during 

 the season 1892. 



The plan of the experiments is an extensive one, but 

 we may say that many of the experiments are designed ta 

 show what manures can be economically applied in the 

 growth of turnips and potatoes in ordinary rotation. 



From the experiments made upon farms at Roth- 

 bury, Ilderton, Tweedmouth, and Wark-on-Tyne, Dr. 

 Somerville concludes that (i) basic slag is the cheapes 

 phosphatic manure, though the best result is obtained 

 with a mixture of slag and superphosphate ; (2) kainit 

 up to 2 cwt. per acre is a profitable dressing to turnips 

 and potatoes ; (3) the turnip crop requires nitrogenous 

 manure ; and (4) small dressings of artificial manures are 

 more directly profitable than large dressings. 



It is to be hoped than many of these experiments will 

 be repeated in the county this year. W. T. 



The Food of Plants. By A. P. Laurie, M.A., B.Sc. 



(London: Macmillan Co., 1893.) 

 This little book is intended to be an introduction to 

 agricultural chemistry. It contains descriptions of a 

 series of simple experiments which may be undertaken 

 without any previous knowledge of chemistry. These 

 experiments illustrate the part: played by water in the 

 nutrition of plants, the nature of the soil and of the air, 

 and how plants obtain their food from these sources, &c. 



The experiments are carefully chosen and described, 

 and can be performed with inexpensive materials, and 

 the book, especially if used as the author suggests, 

 in conjunction with a Chemistry Primer, can well be 

 recommended as an interesting guide to the study of 

 agriculture. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers op, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications. "X 



Fossil Floras and Climate. 



I HAVE read with some interest the communications in 

 recent numbers of Nature based on a review by my friend 

 Mr. Starkie Gardner of a book which I have not yet seen; and 

 as an exile in the south owing to a serious illness, I have not 

 means of reference even to my own papers on the topic in dis- 

 cussion. I think, however, it may be well to direct attention 

 to some Canadian facts published in the Transactions of our 

 Royal Society and elsewhere, to which neither jMr. Gardner nor 

 Mr. De Ranee have referred.^ 



1 See Report of Dr. G. M. Dawson on the 49th Parallel 1875 ; Reports 

 Geol. Survey of Canada, i87i-'77-'79 ; Transactions Royal Society of Canada 

 1883 to 1892. 



