168 Notices respecting New Books. 



Many of these, detailed in the book, can be repeated with the 

 simplest means. A variety of experiments of the greatest interest 

 on simultaneous and successive contrast, positive and negative 

 after-images, flooding, and similar effects demand nothing but a 

 few pieces of white and coloured paper and the like. The con- 

 ditions necessaiy for observing the various entoptic phenomena 

 are also carefully recorded, so that for the experimenter in vision 

 the book is invaluable. There is an excellent discussion of binocular 

 vision. 



On the practically very important subject of testing for colour- 

 blindness our author has naturally much to say, having devoted 

 many years to devising tests for the, Board of Trade and other 

 bodies. He has shown that the old wool test passes fifty per cent, 

 of the colour-blind ! His colour perception lantern, now the 

 official test at the Admiralty and elsewhere, is probably the best 

 device of the kind, but it is expensive and bulky. The new card 

 test just devised by him, and issued by the publishers of the book, 

 is extremely handy and simple to use, while at the same time it is 

 reliable. The ingenious design renders it impossible for the 

 examinee to rely on anything but colour discrimination for reading 

 the cards, which are faithfully reproduced by lithography. We 

 have used the test, and judge that it will be universally adopted 

 where a quick, reliable, and portable test is required. 



Mesures Pratiques en Badioactivite. Par W. Makower et 

 H. Geiger. Tj aduit de l'anglais par E. Philippi. Gautier-Villars. 



This is a translation of the well-known little book of Makower 

 and Geiger, published in this country in 1912 by Longmans. 

 Judging by the places in which we have checked it, the work of 

 rendering it into French has been done carefully and adequately. 

 No alterations or additions seem to have been made. 



Elements of Vector Alc/ebra. By L. Silberstein. 

 Longmans, Green & Co. Price 5s. net. 



This little book is an account of the elements of vector algebra 

 up to and including the meaning and use of the linear vector 

 operator. The convenience of vectors in connexion with the 

 mathematics of physical problems is becoming more widely realized 

 every day ; and we think that there is a real need for a booklet of 

 this character, giving in a few pages just what is necessary as 

 preliminary information for reading any book in which the method 

 is employed. Dr. Silberstein's work is too well known to readers 

 of this magazine for there to be any need for us to speak of the 

 soundness or elegance of the exposition. 



