Septembee 27, 1895.] 



SCmNGE. 



413 



case, and all physicians in cases of doubt make 

 this examination or have it made. Special in- 

 struments like the hsemacytometer of Gowers 

 or Thoma, or the haemaglobinometer of Gowers, 

 have been made for this purpose and can be 

 purchased from all dealers in microscopical in- 

 struments 



The disease known as Filariasis can be and is 

 diagnosed by blood examination. The para- 

 sites causing this disease occur in the immature 

 state in the blood, passing, as they mature, into 

 the lymphatics. These parasites are truly re- 

 markable from the fact that they are found in 

 the blood only at night, being almost or en- 

 tirely absent in the daytime ; if, however, the 

 patient sleep during the day this is reversed, 

 thus showing that the condition of sleep is an 

 important factor in determining the presence 

 the organisms. 



From these facts it would seem that the 

 medical profession is not in quite as ' dense ' a 

 state of ignorance regarding the blood as Prof. 

 Miehels would have his readers believe, and 

 that they do make use of blood examination in 

 the diagnosis of disease. 



Joseph F. James. 

 Washington, D. C, Sept. 4, 1895. 



SCIENTIFIC LITERATURE. 

 The Science of Mechanics. A Critical and His- 

 torical Exposition of its Principles. By Dr. 

 Ernst Mach, Professor of Physics in the 

 University of Prague. Translated from the 

 Second German Edition by Thomas J. Mc- 

 Oormack. The Open Court Publishing Co. , 

 Chicago. 



The Science of Mechanics is an English trans- 

 lation of the German treatise by Professor Ernst 

 Mach, on The Development of Mechanics ; a 

 work whose ability and importance entitle it to 

 critical attention. While not a complete history 

 of the science, it deals with the subject by the 

 historical method and purports to be a philo- 

 sophical discussion of the nature, origin and re- 

 lations of those ideas and principles in mechan- 

 ics which, when thus linked together, give an 

 intelligible and comprehensive view of the 

 science as it now is, and of the sometimes tor- 

 tuous way by which it reached its present state. 

 The book as a whole is unique, and is a valu- 



able addition to any library of science or phil- 

 osophy. 



The author's well-known psychological bent 

 is here directed to getting rid of metaphysical 

 obscurities that befog the discussions of the 

 seventeenth and eighteenth century physicists. 

 He presents mechanics as a physical rather 

 than a mathematical science, employing mathe- 

 matics to some extent, necessarily, but with 

 care not to make of a proposition in mechanics 

 a mere peg on which to hang mathematical 

 formulae. 



After a brief introduction, the work is ar- 

 ranged in a historical view of the development 

 of the principles of statics, to which a hundred 

 and twenty pages are devoted ; then about an 

 equal space is given in the same manner to 

 dynamics, this being the order in which the 

 science actually grew up. These divisions over- 

 lap somewhat, the former being carried well 

 into the eighteenth century, while the latter be- 

 gins with Galileo in the seventeenth century, 

 but the order is, on the whole, very satisfac- 

 tory. 



Although the subject-matter of the first chap- 

 ter may be of less immediate interest than that 

 of the next, yet the author's treatment of it 

 and his philosophical discussion of the early 

 investigators' work and methods of working is 

 most interesting, while the manner in which he 

 shows how a principle has been employed in 

 essence by one and another such investigator in 

 its application to special and apparently unre- 

 lated questions, before some one makes the 

 happy generalization that gives it the force of a 

 law, is admirable. As one example among 

 others,, it is shown how the principle of virtual 

 velocities was made use of by Stevinus in the 

 sixteenth century, and later by Galileo, Torri- 

 celli and others before ' the universal applica- 

 bility of it to all cases of equilibrium was per- 

 ceived by John Bernoulli,' early in the eigh- 

 teenth century. 



' ' They that know the entire course of the 

 development of science will, as a matter of 

 course, judge more freely and more correctly of 

 the significance of any present scientific move- 

 ment than they who, limited in their views to 

 the age in which their own lives have been 

 spent, contemplate merely the momentary trend 



