Helmholtz's treatise physiological optics

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its deductive matter, should bespeak for it a valuable sphere of usefulness in this part of the world. The work constitutes a highly satisfactory collection of theoretical information and material data presented in excellent typoIJUCIEN E. PIOLFT. graphical form. HELMHOLTZ’S

TREATISE

OS

PHUSIOLOGICAL

OPTICS.

Edited third German edition, with appendices. Columbia University. Vol. 3, The Perception numerous illustrations and 6 full-page plates. Optical Society of America, rgz5. Price, $7.

Translated from the by James P. C. Southall. of Vision. x-736 pages. Published by the SW.

The general character of this great work has been set forth in the reviews of previous volumes. This is the closing volume. The text has been translated from the German and the editor has been assisted by a number It is the largest volume of the series and is crowded with of specialists. The text with some small exceptions information upon the subject of vision. nature of many of is wholly from the German. Owing to th e metaphysical the questions that arise in the presentation of the subject, the editor has found the translation far more difficult than that of other portions of the work, but we may be sure that his rendering is trustworthy and in good English. The German of the profound professors who use that language is by no means always as clear as could be wished, and we are not astonished that the translator has met with serious difficulties, but we may feel sure that the essential The volume meaning of all portions of the text will be found in this translation. is sumptuously printed and as the final one of a work of unquestioned excellence, it will bc welcome to all interested in the field to which it is devoted. HESRY METAL SPRAYIXG.

The origin,

development

process of metallization. By T. Henry lurgy, the University of Birmingham, author of “ Cadmium : Its Metallurgy,

and applications

TXFFMA?;~\J.

of the metal-spray

Turner, M.Sc., Lecturer in Metaland N. I?. Budgen, M.Sc., Ph.D., Properties and Uses.” xiv-175

pages, 9 x 6 inches, cloth, with 165 figures. London, Charles Griffin and Company; Philadelphia, J. B. Lippincott Company, 1926. Price, $6.50. Compared with other processes of applying protective and ornamental metal coatings, metal spraying is a relatively recent development. Apart from its other merits, it possesses the important advantage of applicability to finished objects in sitzc. In fact, its method of application is not unlike that employed in spraying paint upon finished structures. The apparatus which is employed for that purpose is aptly called by its inventor, Dr. M. U. Schoop, of Zurich, “ a spraying pistol,” for it seems it was the effect of the impact of a smallcalibre bullet upon a metal target that suggested the method. The authors, by availing themselves of the extensive collection of monographs on the subject which have appeared from time to time in periodical