Notices respecting New Books. 363 



each spectrum the exact similarity in constitution is doubtful, 

 and this I have attributed more to inaccuracies in the measure- 

 ments in this part of the zinc and cadmium spectra than to 

 any differences in physical characters of the lines. As far as 

 recorded observations show, the last group of five lines appear 

 to be homologous in the three spectra. They are all con- 

 tinuous lines, sharp, and only slightly extended, but exhibit- 

 ing certain differences which might be accounted for by the 

 atomic mass of the elements being different 



It may be remarked that Mr. Ames appears to have worked 

 only with arc-spectra, and thathe has had the advantage of using 

 a Rowland concave grating of great power ; notwithstanding 

 the amount of dispersion at command, the lines which he 

 describes as single are single in my spectra, and those which 

 he finds to be double are also described as such by me. In 

 fact, by the use of prisms for photographing, and a magni- 

 fying power of from 25 to 50 diameters for examining the 

 photographs, an extraordinary dispersion in the ultra-violet 

 is easily obtained. There are some advantages in the use of 

 prism-spectra, first, because there is very little loss of light 

 and the exposure is not unduly prolonged ; secondly, the dis- 

 tinctive features of the lines are much more pronounced. 



The study of homologous spectra I believe will lead to an 

 elucidation of the constitution of the chemical elements ; but 

 before this field of inquiry can be made highly productive 

 there is need for a revision of the wave-lengths of some of the 

 extreme rays in the ultra-violet spectra, and we require also 

 a means of photographing wirh facility from wave-lengths 

 2000 to 1800 or further. 





XL II. Notices respecting New Books. 



A Short Course of Experiments in Physical Measurement. By 

 Harold Whiting, Instructor in Physics at Harvard University. 

 Part II. : Sownd, Dynamics, Magnetism, and Electricity. (Cam- 

 bridge, Massachusetts : John Wilson & Son.) 



rFHE volume before us is issued as the second part of an 

 J- elementary treatise on practical physical measurements, of 

 which the first part was published about a year ago, aud has 

 previously been noticed in this Magazine. A hope was then 

 expressed that the figures and pictures of apparatus would be 

 improved in the succeeding volumes, but we regret that this hope 

 has not been realized. On opening the book we are immediately 

 confronted by some of the worst woodcuts which we ever 

 remember to have seen in any scientific work. In the case of 

 simple diagrams, where there are no shaded parts, the figures are 



