Apeh, 14, 1916] 



SCIENCE 



535 



was clearly the result of keeping the animal in 

 water pumped from New York Harbor, the 

 only supply available for the large floor pools, 

 under present conditions. 



The water of the harbor is always of low 

 salinity and is charged with sewage, its foul- 

 ness being especially noticeable in midsummer. 



The propoise had grown perceptibly since 

 its arrival on November 15, 1913. Its weight 

 at death was 293 pounds and its length eight 

 feet. Four other porpoises received at the same 

 time lived seven months in captivity, when 

 they died of pneumonia in rapid succession. 



Like the one referred to above their skins at 

 death were also filth-infected, although not to 

 the same extent. Our experience has shown 

 that the porpoise readily endures captivity and 

 might live much longer if pure sea water were 

 available. Other porpoises will be obtained and 

 equipment is now being installed for filtering 

 the harbor water — an improvement that has 

 long been needed at the Aquarium. 



The school of porpoises contained both sexes 

 and they were often observed mating. The 

 loss of the females was especially disappoint- 

 ing as the prospects for breeding in captivity 

 were promising. 



All of these porpoises were constantly active 

 and playful to within a few days of their 

 deaths. 



c. h. townsend 



The New York Aquaeium 



SCIENTIFIC BOOKS 



A Treatise on Light. By E. A. Houstoun, 

 Lecturer on Physical Optics, University of 

 Glasgow. Longmans, Green and Co., 1915. 

 Pp. 478. $2.25 net. 



To the student of optics familiar with the 

 treatises of Drude, Preston, Shuster and "Wood, 

 and numerous other text and reference books 

 on optics, there would appear to be little need 

 for a new text in this field. Professor Hous- 

 toun's treatise is, however, unique in scope and 

 treatment, and will doubtless prove of great 

 value both as a text and for reference. 



In scope, this treatise covers both theoretical 

 and physical optics, together with geometrical 

 optics, vision, photometry, illumination, spec- 



troscopy and X-rays. Part I. deals with Geo- 

 metrical Optics, Part II. with Physical Optics, 

 Part III. with Spectroscopy and Photometry 

 and Part IV. with Mathematical Theory. An 

 extremely concise treatment of each subject 

 makes it possible to cover this wide field in so 

 few pages, the style is lucid and free from vax- 

 necessary explanation and deductions. Ex- 

 cept, perhaps, in the chapter on the nature of 

 light, the treatment is nowhere exliaustive or 

 profound, and is well adapted to the use of 

 advanced undergraduate students. 



Part I., on Geometrical Optics, deals in 

 seven chapters with the elementary theory of 

 image formation, the theory of the simple 

 optical instruments and the determination of 

 refractive indices. The third order defects of 

 images (Seidel aberrations) are barely men- 

 tioned. This section of the book, while an ex- 

 cellent teaching text in that it presents a well- 

 balanced outline of the subject, would be much 

 more valuable if it included a little modern 

 technical optics dealing with lens calculation, 

 the third-order aberrations and precise meth- 

 ods of testing. 



The hundred pages on Physical Optics is a 

 discussion of the velocity, interference, diffrac- 

 tion and polarization of light in six chap- 

 ters. A rather full treatment of the diffrac- 

 tion grating is given, but otherwise the matter 

 presented is quite academic and very concise. 

 On page 190 statements (3) and (4) regarding 

 interference between two beams of plane polar- 

 ized light evidently require revision. The 

 description of improved polarizers and anal- 

 yzers does not mention those devised by Brace 

 and used with such success by his students. 



Part III., entitled Spectroscopy and Pho- 

 tometry, contains two chapters on the spectro- 

 scopy of the visible spectrum, a chapter on the 

 ultra-violet and one on the infra-red and 

 X-rays. The remaining three chapters are 

 devoted to Photometry and Spectrophotometry, 

 the Eye and Color Vision and Lamps and 

 Illumination. 



The two chapters on general spectroscopy, 

 for their length, could hardly be improved upon 

 in choice and presentation of material. The 

 chapter on the ultra-violet impresses the re- 



