July 4, 1890.] 



SCIENCE. 



1 1 



only one in the modern technical literature of machine design, of 

 this character, so far as we know, which includes the now well- 

 known facts relating to the modification of the laws of solid fric- 

 tion by the introduction of the lubricant. The experiments of 

 Hirn, who first discovered this modification, are alluded to, and 

 those of Tower are given considerable attention; but, curiously 

 enough, those of Thurston and of Woodbury in this country, 

 ■which have been vastly more extensive, and which relate much 

 more closely to the conditions of familiar ordinary practice, are 

 not even mentioned, though they are now the basis of all rational 

 work in the proportioning of journals, under other conditions than 

 those of the Morin experiments, or of the comparatively rare ''oil- 

 bath" lubrication. 



Elementary Dynamics of Particles and Solids. By W. M. Hicks. 

 London and New York, Macmillan. 12°. $1.60. 



This closely printed text-book, in the neat standard style of the 

 Macmillans' publications of the class, is a well-written treatise on 

 the elements of mechanics for schools and colleges. It is sub- 

 stantially of the same grade, and of similar extent, with those 

 familiar to teachers as usually adopted in the English institutions 

 •of learning. In such a case there is little opportunity for origi- 

 nality, and the subject admits of but little safe or profitable 

 variation from the almost universal and standard methods of 

 treatment. As stated by its author, the chief points of novelty 

 are the consideration of the division of statics as a special case of 

 kinetics, and the methods of discussion of the ideas of mass and 

 of momentum, which are considered before taking up the ideas 

 of force and resistance. This the author thinks the best, if not 

 the only logical, order of procedui'e; and especially so, as the 

 ■whole must be subject to confirmation and proof experimentally. 

 He would establish his work on this basis, rather than upon the 

 ■usual system of assumption, from experience, of general laws, 

 and a logical construction of the science by building upon those 

 laws. The work is well done, and, for those who prefer this 

 method of treatment, it will be found an excellent text-book. 

 The order of treatment is, (1) rectilinear motion of a particle, (3) 

 forces in one plane, (3) motion of rigid bodies. An unusually 

 rich collection of problems and examples is given. 



Tbe second part includes the study of machines and the modi- 

 :flcation of their efHciency by friction; the book being intended, 

 as the author says, to meet the wants of mechanical engineers, as 

 well as the classes of schools and colleges. It will hardly meet 

 the needs of that class, however, as it is far too elementary and 

 incomplete, as a system of applied mechanics, for their purposes. 

 The treatment of the machines is the ancient one of studying 

 the "six" (?) elementary machines, considering the inclined plane 

 and the screw as different in principle, and the lever and the 

 wheel and axle as different elementary machines. They are well 

 treated. In the chapter on friction we have an example of the 

 curious persistence of ancient and obsolete notions among the 

 writers of text-books, who seem rarely to keep themselves abreast 

 of the progress of research. The old notions of Coulomb are here 

 made the basis of the study of friction losses of energy; and the 

 author of the book seems entirely unaware that they have been 

 obsolete, as respects lubricated surfaces, since the days of Hirn's 

 investigations a generation ago. The young engineers of to-day 

 might give such writers useful hints. The table of co-eflScienls 

 of friction (six constants) is from the now almost forgotten work 

 of Morin. They are, of course, correct for the conditions under 

 which they were obtained, but not for other and the various usual 

 conditions of machine operation; and no clew is given to the lim- 

 itations of their application. The distinctions between friction of 

 solids, friction of fluids, and '-mediate" friction, are not alluded to. 



^ems and Precious Stones of North America. By George F. 

 KuNZ. New York, The Scientific Publishing Company. 4°. 

 $10. 



The author of this book is connected with the world-renowned 

 firm of Tiffany & Co., and in his employment by this house as a 

 gem expert has had a rare opportunity to become acquainted with 

 the matters of which he treats in the book before us. Further, 

 this expert knowledge has led to the employment of Mr. Kunz by 



the United States Geological Survey on special investigations, 

 which have made him the more conversant with his subject. 



It may be asked, Are any gems found in North America? This 

 question evidently presented itself to our author, as he opens his 

 somewhat large treatise with the statement that gems are found 

 here in great variety, but that there has been little systematic ex- 

 ploration for them, as the indications are not such as to justify the 

 employment of large capital in the search. In fact, a week's 

 yield of the granite-quarries exceeds in value the yearly output of 

 gems the country over; and a day's yield of the South African 

 diamond-mines is of more value than the year's yield of all gems 

 in North America. 



It is not to be supposed, however, that there is no search going 

 on in this country for gems, or that cases are unknown in which 

 persons for a while believe themselves the possessors of stones of 

 great value found in their corn-field or sheep-pasture. Reports 

 of such finds are constantly coming in, and many of them reach 

 the jewelry house of Tiffany & Co. The stories of these deceptive 

 stones, as told by Mr. Kunz, are interesting, and show that a book 

 of the kind he has now brought out, if available in the libraries 

 of the country, might quickly explain to the possessor of a green 

 stone the differences between colored quartz and emerald. 



Nine chapters are devoted to the gems of North America, in 

 which descriptions are given of the gems, and chemical analyses 

 to show their composition. A chapter follows on pearls, in which 

 due attention is paid to the method of their formation. There are 

 then two chapters on tbe precious stones of Canada and of Mexico 

 and Central America. The book closes with two chapters de- 

 voted to aboi'iginal lapidarial work in North America, and to the 

 commercial value and uses of gems. 



Aside from the gems found in this country, there is, as wealth 

 accumulates here, a constant increase in the number of interest- 

 ing gems held here by collectors, and of these Mr. Kunz has 

 something to say. 



The undoubted standing of Mr. Kunz as an authority on gems 

 makes this work a real accession to the number of books to which 

 one may turn for information; and, though the annual commer- 

 cial output of gems is small in North America, we feel sure, es- 

 pecially as so many cognate subjects are treated within the book's 

 covers, that there will be many — collectors and artisans — who will 

 find it a help. 



The execution of the book is to be praised in most respects, — 

 the beauty of the colored plates, which are numerous and add 

 much to its usefulness, is especially noticeable, and the general 

 typographical appearance is excellent, — but there was evidently 

 something wi-ong with the proof-reading, which left a long list of 

 errors to be corrected in the unsatisfactory way of a list of er- 

 rata. 



AMONG THE PUBLISHERS. 



Those who are interested in the uses, tests for purity, and 

 prepai-ation of chemical re-agents employed in chemical, micro- 

 scopic, or petrographic analysis will find much valuable informa- 

 tion in "Chemical Re-agents," by Charles O. Curtman, M.D., 

 recently published by the John L. Boland Book and Stationery 

 Company, St. Louis. 



— Messrs. Longmans, Green, & Co. have issued a ' 'Junior 

 School Algebra." The author is William S. Beard, assistant 

 master in Christ's Hospital. The book is intended for use in pre- 

 paratory schools. 



— "School Hygiene," by W. J. Abel, recently issued by Long- 

 mans, Green, i&Co., contains simple directions respecting ventila- 

 tion, eyesight, infectious diseases, and first aid in injuries. Thei'e 

 is no attempt to explain the why and wherefore of the courses of 

 procedure recommended. The manual is intended, as its title 

 suggests, for use in schools, and it aims to describe what to do 

 and how to do it, in case of diseases, accidents, etc. 



— The leading articles in Babyhood for July are, '-Fruit for 

 Children," by J. W. Byers, M.D.; "Weaning," by D. Warman, 

 M.D ; '-The Kindergarten on the Farm" (continued series), by 

 Adele Oberndorf ; and "The Baby's Mind," by EUzabeth S. Brown, 



