PROF. HENRICI can always be depended upon to embellish any mathematical subject which he touches, because, with the skill of the analyst, he combines the keen perception of the geometer, which ever seeks to render the results of analysis in some way visible by spatial representation—or, perhaps, to reach the results directly (and often more simply) without any aid from analysis at all. To a mathematician of this kind the subject of vector analysis is peculiarly appropriate. We are therefore indebted to Mr. Turner for putting into systematic form the lectures delivered by Prof. Henrici at the City and Guilds Technical College, and producing a very simple and elementary work the methods and ideas of which should find a very early introduction into our ordinary mathematical teaching. Vectors and Rotors, with Applications. By O. Henrici G. C. Turner Pp. xv + 204. (London: Edward Arnold, n.d.) Price 4s. 6d.