248 



NATURE 



July 4, 1878 



number of figures, and in addition to numerous unsolved 

 exercises, has given very many worked-out problems. In 

 his introduction he points out that " the practical man, 

 unlike the theoretical, cannot choose his problems ; he 

 must take those which the requirements of his art present, 

 whether elegant and curious, or cumbrous and repulsive. 

 Moreover, in his case, some solution of every problem 

 must be obtained ; if he is unable to find a rigorous 

 scientific solution he must make some further assumptions 

 or have recourse to experiment ; he cannot lay the ques- 

 tion aside." He goes on further to point out the 

 differences between the two studies of theoretical and 

 applied mechanics. The author has brought the subject 

 before the notice of mathematicians in communications 

 to the Mathematical Society and the Educational Times. 



Mr. Loewy has retained much of the elementary part of 

 the late Dr. Lardner's treatise, having carefully revised it 

 and brought it up to modern requirements. He has 

 re-written, for the most part, the descriptive chapters on 

 machines, clockwork, &c. Many new illustrations and a 

 great number of solved exercises have been added, so 

 that now the work is embellished with nearly 400 illus- 

 trations. An account is given of the modern units of 

 force and work (the dyne, poundol, &c.). The result is a 

 neat and readable book on properties of matter, theory of 

 machinery, and illustrations of the application of me- 

 chanical principles in the industrial arts. We do not 

 pretend to have read the work for it is full of matter, but 

 what we have examined we have found interesting and 

 carefully done. We have detected a few slips (typo- 

 graphical, chiefly) in the solutions. A good feature is an 

 index. 



The last book on our list is neatly got out and is 

 doubtless adapted for the end in view, the author having 

 written it for candidates for the Oxford and Cambridge 

 Local Examinations. It is such a book as might have 

 been compiled at any time within the last twenty-five 

 years from the Cambridge text-books, for it keeps quite 

 to the old Cambridge *' lines ; " it " aims at being simple, 

 but not childishly so." The modern treatment of the 

 subject has been altogether avoided. This is, perhaps, 

 no fault of the author, but rather the exigencies of the 

 above-named examinations have compelled him to move 

 in this rut. There is a sufficient number of exercises 

 taken from the examination papers, and a chapter is 

 devoted to hints for, and examples of, the selection of 

 problems. The figures generally are clearly drawn, but a 

 cylinder on p. 43 is a sorry representation of such a 

 solid. 



OUR BOOK SHELF 



Mikrographie der Glasbasalte von Hawaii : Petrogra- 

 phische Untersttchung. Von C. Fr. W. Krukenberg. 

 (Tiibingen, 1877.) 



The interesting facts made known of late years by Prof. 

 Mohl, of Cassel, and Dr. Boficky, of Prague, as the 

 result of their study of the microscopic characters of the 

 vitreous and semi-vitreous rocks of basic composition, 

 have rendered it eminently desirable that a thorough inves- 

 tigation of the remarkable lavas of the Sandwich Islands 

 should be undertaken by some competent observer. We 

 therefore hail the appearance of the monograph now 

 before us as supplying a want which has been felt for 



some time past by all who are interested in micro-petro- 

 graphic studies. 



From the older analyses of the Sandwich Island lavas 

 as tabulated by Herr Krukenberg, we learn that the 

 composition of these rocks varies within very wide 

 limits — the proportion of silica ranging from 3974 to 

 59"8o ; the author's own analyses, however, would seem 

 to indicate much less widely separated rocks as having 

 been subjected to examination by him, for the propor- 

 tions of silica are given as from So'865 to 53"6i. The 

 most remarkable circumstance about the composition of 

 these Hawaiian lavas is probably the large proportion 

 of iron-oxide which they contain, the percentage of this 

 substance ranging from 13 to 33 per cent., while alumina 

 is only present in small quantity, or is sometimes alto- 

 gether absent. 



Herr Krukenberg first describes the curious structure 

 revealed by the microscope in the compact basaltic glass 

 in which are detected numerous beautiful examples of 

 those skeleton crystals built up of crystallites to which 

 Vogelsang first directed the attention of geologists, and 

 to which the name of "chiasmoliths" has been applied. 

 Among the perfectly-formed crystals porphyritically 

 embedded in this compact or glassy mass, the author 

 noticed felspar (both orthoclastic and plagioclastic) and 

 olivine, but he failed to detect augite. 



The curious forms assumed by the threads of Pele's 

 hair are admirably described in the work before us, and 

 are illustrated by numerous figures. Gas bubbles appear 

 to be very common in these glass threads, and they are 

 often drawn out into elongated cavities or fine capillary 

 tubes. Minute crystals are sometimes seen in the midst 

 of the glass threads, which sometimes exhibit a concentric 

 structure and at others a series of transverse striations. 

 In the ordinary porous glass lava the author finds struc- 

 tures intermediate between the chiasmoliths and the crys- 

 talline plates seen in Pele's hair; his drawings, indeed, 

 very admirably illustrate the mode of development of 

 crystals in glassy magmas. The last variety of the Sand- 

 wich Island lavas described in this monograph is the 

 sphaerulitic ; but the sphaerulites of the basaltic rocks do 

 not appear to differ in any essential point of structure 

 from those so well known as occurring in acid vitreous 

 rocks. 



In an appendix to the paper the author notices the 

 existence in the Sandwich Islands of a true obsidian which 

 yielded 76'io per cent, of silica. The monograph is illus- 

 trated with four lithographic plates, and is a very valuable 

 contribution to petrographic science. J. W. J. 



Preventive Medicine in Relation to the Public Health. By 

 A. Carpenter, M.D., C.S.S., Camb. (London : Simp- 

 kin, Marshall, and Co.) 



Under the title of "Preventive Medicine" Dr. Carpenter 

 has reprinted lectures which he gave, during the summer 

 session of 1876, at St. Thomas's Hospital. They were 

 addressed to students, and the form in which they were 

 first given has been preserved. At a time when, in the 

 words of the Prince of Wales' s letter to the Society of 

 Arts, " the supply of pure water to the population is ex- 

 citing deep interest throughout the country," the volume 

 will be found a convenient and ready rhum^ for those 

 who wish to inform themselves on the more important 

 questions that enter into the consideration of what is a 

 good water supply, and what is to be done with fouled 

 water. As is well known. Dr. Carpenter advocates 

 sewage-farms as the proper way to dispose of sewage, 

 and the chapters devoted to this subject enter into 

 financial as well as scientific consideration. In speaking of 

 the spread of epidemic diseases by water and by air Dr, 

 (^arpenter explains the germ theor}^, but we cannot find 

 that he even alludes to any other possible explanation. 

 It appears as if he regards the germ theory of disease as 

 really /r<?z/^^. Is it ? 



