7 oo SCIENCE PROGRESS 



The book is clearly and forcibly written and can be recommended to all 

 interested in the subject as well as to those who wish to begin its study. 



R. W. Forsyth. 



An Atlas of Absorption Spectra. By C. E. Kenneth Mees, D.Sc. [Pp. 74.] 

 (London : Longmans, Green & Co. Croydon : Wratten & Wainwright, Ltd. 

 1909. Price 6s. net.) 



During the special researches necessary for the production of satisfactory photo- 

 graphic dyes and light-filters, the workers in Messrs. Wratten & Wainwright's 

 laboratories at Croydon were forced to prepare an atlas of absorption spectra, 

 because no such atlas, dealing with the less refrangible end of the spectrum, was 

 available. Dr. Mees now publishes the result of their compilation with suitable 

 explanations and indices. 



The volume contains the photographic absorption curves of 170 dyes in 

 common use and 76 filters ; each curve is fitted with a wave-length scale and 

 ordinates showing " intensities." The photographs from which the curves are 

 reproduced were taken with a specially designed spectrograph, the apparatus and 

 method being fully described in the text. 



The first requirement was to eliminate, so far as possible, the selective sensitive- 

 ness of the plate employed; to this end, "Spectrum Panchromatic " plates were 

 used in conjunction with a suitable standard filter, the combination giving a fairly 

 flat colour curve between XX 7200 and 3900. Solutions of the dyes in pure water 

 were placed in front of the slit in a rectangular vessel divided into two wedge- 

 shaped compartments : one compartment contained the solution of the dye under 

 examination, the other pure water. In this way the thickness of the solution 

 traversed by the beam of light from a Nernst lamp was varied, along the slit, and 

 the photographs indicate the absorption effects of different thicknesses of the 

 solution, or, what is nearly the same thing, the variation of the absorption with the 

 concentration. This device being impracticable with the filters, the variation in 

 intensity was attained by the interposition of a wedge of neutral-tinted glass. 



Of the photographic maps themselves but little can be written, except that 

 they are excellent and should prove exceedingly useful in the many departments 

 of scientific research where it is now so desirable to employ light of a restricted 

 wave-length range. Where the amount of light available is unlimited, there 

 should now be no difficulty in referring immediately to a dye, or a filter, which 

 will give almost any desiderata in this direction. The indices given by Dr. Mees 

 explain succinctly the nature and source of the dye employed in each case, the 

 strength of the solution used in the test and the stability of the dye under the 

 action of light. Each filter, also, is indexed under its special designation. 



In the investigation of "colour" in photographic processes Dr. Mees occupies 



a pre-eminent position, and we welcome this atlas with the assurance that the 



results are based on truly scientific bases and will greatly facilitate research in 



many branches of science. 



W. E. Rolston. 



Dynamo Laboratory Manual : Vol. I. Direct current Studies and Tests. By 

 William Suddards Franklin and William Esty. [Pp. viii + 152.] 

 (London : Macmillan & Co., Ltd., 1909. Price 7s. 6d. net.) 



A LABORATORY manual of any kind is always sure of two attacks ; one set of 

 critics say it tells the student too much, the other that it tells too little. 



Each set may be justified in its criticisms, because everything depends on 



