204 



NATURE 



[November 15, 191 7 



this not the case and we are glad when the 

 speaker sits down. There is an excellent chapter 

 on "stuttering," with many wise suggestions. 



J. G. M. 



Practical Cheesemaking : A General Guide to the 



Manufacture of Cheese. By C. W. Walker- 



Tisdale and Walter E. Woodnutt. Pp. 182. 



(London: Headley Bros., Ltd., 1917.) Price 



45. 6d. net. 

 This book deals with the technical side of cheese- 

 making, and is intended to serve both as a text- 

 book for dairy students and as a reference-book 

 for practical cheesemakers. The subject-matter is 

 well chosen, and whilst the explanations which are 

 given at each stage are clear and simple, there 

 is a great deal of practical information which it 

 has previously been difficult to obtain in print. 



Very properly, a considerable amount of space 

 is devoted to the composition of milk and the 

 methods which must be adopted if a milk suitable 

 for cheesemaking is to be obtained. This side of 

 the subject cannot be put forward too strongly, 

 for, unless the cheesemaker can start with a 

 reasonably pure product, no skill on her part, can 

 turn it into really first-class cheese. 



Full working details of the methods used in 

 analysing milk by the Gerber test and by the 

 lactometer are given, also the usual tests for 

 obtaining information as to the purity of the milk 

 in respect of cleanliness. The nature and pre- 

 paration of rennet are dealt with, and instruc- 

 tions given for the making Of home-made rennet. 

 The chapter treating of starter is a particularly 

 good one, from both the theoretical and the prac- 

 tical points of view. 



About half the book is devoted to the practice 

 of cheesemaking, and the preparation and pro- 

 perties of all the best-known British varieties are 

 dealt with in detail. This portion of the book is 

 to be strongly recommended, for the authors' 

 wide practical exp>erience is drawn upon with the 

 best results. The chapter on faults or defects of 

 cheese should also be specially noticed. 



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 intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



On an Appearance of Colour Spectra to the Aged. 



May I suggest that the aippearances described by Mr. 

 R..Brudenell Carter in Nature of November i all 

 harmonise with the assumption that their cause is in 

 some way due to diffraction ? 



The fact of the blue internal band and the red ex- 

 ternal band, and that the diameter of the colour circle 

 increases in size in approximate ratio to the distance 

 of the light viewed, seems clearly to point to this", no 

 less than the fact that when the pupil is contracted, 

 or when the lig^it is viewed through a pinhole, the 

 appearances vanish, because the actual number of 

 diffracting elements upon which the light impinges 

 would then be too small to give rise to the appearance. 



hO. 2507, VOL. 100] 



The spacing and the number per unit area of the 

 diffracting elements could readily be estimated from 

 the data so clearly given. Whether they take the form 

 of particles or of lacunae in the humours of the eye, or 

 whether due to some alternating structure of the lens, is 

 a matter on which I am not competent to express any 

 opinion. 



It is interesting that Tyndall had a somewhat similar 

 case brought to his notice, to which reference is made 

 in his " Notes on Light " delivered at the Royal Institu- 

 tion in 1869 (Longmans, Green and Co., 1890, p. 54) 

 in the following words : — 



" One of the most interesting cases of diffraction by 

 small particles that ever came before me was that 

 of an artist whose vision was disturbed by vividl}^ 

 coloured circles. When he came to me he was in great 

 dread of losing his sight, assigning as a cause of his 

 increased fear that the circles were becoming larger 

 and the colours more vivid. I ascribed the colours to- 

 minute particles in the humours of the eye, and en- 

 couraged him by the assurance that the increase of size 

 and vividness indicated that the diffracting particles 

 were becoming smaller, and that they might finally be 

 altogether absorbed. The prediction was verified." 

 Julius Rheinberg. 



23 The Avenue, Brondesbury Park,' 

 London, N.W.6, November 5. 



I AM much obliged to you for permitting me 

 to see Mr. Rheinberg 's interesting letter, and 

 am humiliated by the proof of my forgetful- 

 ness of the passage from Tyndall, which I 

 must often have read in past years. But, as a patho- 

 logist, I incline to my supposition of lenticular in- 

 efficiency, perhaps only an excess of that which is 

 universal as life advances, for I do not see how the 

 occurrence of a cloud of particles in the ocular media, 

 in otherwise healthy and perfectly effective organs, is 

 to be explained. Nor is it probable that the cloud, if 

 it existed, would be of similar density in the two eyes, 

 or that it could exist at all without some impairment of 

 sight. In my own case, at least, the colour circles 

 of the two eyes are of equal size and brightness. 

 R. Brudenell Carter. 



76 South Side, Clapham Comman, S.W.4, 

 November 10. 



Paraffin a Scottish Product. 



In Lt.-Commdr. Wimperis's interesting article on 

 " Coal-gas for Motor Traction," which appears in 

 Nature of November i, he says: — "Paraffin can be 

 used quite well on slow-moving vehicles . . . but this, 

 again, is not home-produced." 



I should like to point out that paraffin is, and always 

 has been, a Scottish product ; and it is fortunate in- 

 deed for the country that it is so. No doubt Lt.- 

 Commdr. Wimperis is thinking of the similar 

 petroleum products which are imported, but paraffin oil 

 distilled from shale is exclusively a home product. So 

 satisfactory is paraffin oil as an engine fuel that it has 

 been adopted by the Board of Agriculture for Scotland 

 for use by their agricultural tractors on its merits in 

 preference to the foreign product. 



H. R. J. Conacher. 

 - High Holm, H^orsewood Road, Bridge of Weir, 

 November 3. 



Mr. Conacher is quite right. I should have said 

 that before, the war Scotland was able to produce a 

 very useful,, though small, percentage of our home de- 

 mand for paraffin. What the proportion may be now 

 I do not know. H. E. Wimperis. 



November 8. ,. ' 



