96 



KNOWLEDGE. 



[April 1, 1897. 



Pritcbard's method in his astronomical work ; for it was a 

 point with the latter to take up a definite research and then 

 carry it to a distinct completion, "leaving no straggling 

 ends to be gathered together after his death." 



His career as a schoolmaster, first at Stockwell Grammar 

 School, then at Clapham, occupied nearly thirty years, 

 from 1883 to 1862. The eight following years, the story 

 of which is told by his daughter, Miss Rosalind Pritchai'd, 

 were spent at Freshwater. This was the time in which he 

 served the Eoyal Astronomical Society in the successive 

 important ofiices of Secretary, Vice-President, and Presi- 

 dent. AVith his removal to Oxford in 1870 he entered on 

 an entirely new career — depicted to us from the point of 

 view of his family by Miss Ada Pritchard, from that of his 

 profession by his successor Prof. Turner ; whilst the Bishop 

 of Worcester, as an old and intimate friend, deals with his 

 theological work. 



That the life of a man so original and many-sided 

 should have been entrusted not to one writer but to several, 

 each dealing with that phase for which they were best 

 equipped, and yet all combined in one harmonious whole, 

 renders the book a vivid — one might say a stereoscopic — 

 representation of its subject, and frees it from that bane 

 of biography — monotony. 



And the book will be valuable not merely as a portrait 

 or from its quick interest. Prof. Pritchard's example, his 

 earnestness, sincerity, and method, may well inspire many 

 a worker, and teach to others the joy he felt himself : 

 "We are never so happy as when we have a little too 

 much to do, and do it." 



The Collector's Manual of British Land and Freshwater 

 Shells. Second Edition. By L. E. Adams, B.A. (Taylor 

 Bros., Leeds.) Illustrated. A Monograph of the Laiid and 

 Freshwater Mollusca of the British Isles. By .J. W. Taylor, 

 F.L.S. (Taylor Bros., Leeds.) In three parts. 6s. each. It 



Anodonia ci/gnea (L.), Saudwill Park, Stall'L'nl^llil•o, collected by Mr. J. 

 Madison, sliowiiig the effects of some severe laceration of the mantle, the 

 result of which is seen in the strong'y separated parts of tiie left valve and 

 in the deeph -furrowed right valve. From "A Monograph of the Land and 

 Freshwater Mollusca of the BritiBh Isles." 



would have been matter for regret had not this " Collector's 

 Manual," with its well-pourtrayed figures and valuable 

 original observations, met with due appreciation by those 

 interested in the freshwater mollusca. The author has a 

 true perception of the spirit of scientific research, which is 

 significantly displayed in the generalizations drawn from 

 the many years' systematic examination of specimens 

 gathered from every part of the island, the total result 

 forming a valuable acquisition for the conchologist. The 

 discrimination exhibited in the compilation of the elaborate 

 synoptical tables is beyond praise, and this part of the 

 work may be recommended to the notice of beginners as 

 being specially useful in comparing new finds. The 

 " Monograph of the Land and Freshwater Mollusca," by 

 Mr. Taylor, brings together, as far as practicable, aU reliable 

 information bearing upon the study of this subject, not 

 from the specialist's point of view, but in a way which aims 

 at combining all the many aspects of this department of 

 knowledge. An excellent coloured frontispiece accompanies 

 each part, and there are hundreds of other illustrations of 

 the very highest character as regards artistic eii'ect. The 

 descriptive part is clear, comprehensive, and accurate, 

 and, best of all, bristles with original observations which 

 entirely eliminate the dry-as-dust element often associated 

 with such works. A curious monstrosity or malformation 

 is here reproduced which will convey some idea of the 

 quality of the illustrations. 



Miseelhineous Papers. By the late Prof. Heinrich Hertz. 

 With an Introduction by Prof. Philipp Lenard. Authorized 

 English Translation by D. E. Jones, B.Sc, and G. A. 

 Schott, B.A., B.Sc. Pp. 340. (Macmillan.) lOs. 



It is impossible to do justice to the contents of this 

 volume in the brief space of a review. We cannot even 

 refer to all of the twenty-two papers it contains, much less 

 set forth their scope and teaching. Most of the papers 

 describe the earlier investigations which Hertz 

 carried out before his great electrical researches. 

 At the age of twenty-one he began his first inde- 

 pendent research at Berlin, while a pupil of "\'on 

 Helmholtz and Kirchofl'. The subject — electric 

 inertia — offered dilSculties which many experienced 

 investigators had been reluctant to attack, while, at 

 the same time, only a negative result could be antici- 

 pated. But Hertz finished the task, and was able 

 by his experiments on the magnitude of the extra 

 current to assign an upper limit to the kinetic 

 energy of electricity in motion. His next paper was 

 more theoretical, but, nevertheless, was of extreme 

 value, and it is so rare that physicists will be glad 

 to find a translation of it in the present volume. 

 The subject is "Induction in Rotating Spheres." 

 The currents induced in moving masses of metal 

 by magnets had been studied by Arago, Faraday, 

 and others, and Maxwell had worked out the theory 

 of the currents induced in a thin plate, showing also 

 how it could be applied to Arago's disc. But it was 

 left to Hertz to solve the problem of the case of a 



/, solid or hollow sphere rotating about a diameter, 

 y when the hiduciug magnets were outside, or, in the 

 r , latter case, inside, the sphere. 



In 1882 Hertz began his investigations of the 

 electric discharge in gases, and before a month had 

 passed he discovered a curious characteristic of the 

 spark discharge. Then came his paper on the 

 cathode rays, for the study of which he fitted up a 

 battery of one thousand secondary cells. To the 

 majority of people the cathode rays are but things of 

 yesterday, and even to many men of science the fact 

 that Hertz arrived at the following conclusion will 



