422 



THE POPULAR SCIENCE MONTHLY 



guishment in logic of questions of origin and 

 validity. The difference between reality as un- 

 derstood in ordinary belief, and as the term 

 is applied to science, is very definitely dealt 

 with in the essay on What is Reality? also 

 the query as to whether our feelings are more 

 than our thoughts, and if space is actually 

 occupied by the real. On the Phasdo of 

 Plato, the most interesting of the critical 

 examinations apply to the distinction that 

 ought to obtain between Plato's teachings as 

 understood by himself, and as they are sub- 

 sequently developed and interpreted by Aris- 

 totle. Comparing the arguments of the 

 Phjcdrus with those of the Phiedo, some 

 technical points arise in the mind which Mr. 

 Ritchie deems worthy of especial comment. 

 Some striking objections to the position of 

 Economics considered in its relation to the 

 sciences are concisely recounted, and in 

 Locke's Theory property the author sug- 

 gests an interesting study on the theories of 

 Hobbes and Locke in the light of events cur- 

 rent in their day. 



When the work is considered as a factor 

 in modern research, each page and para- 

 graph may be regarded as a brief historical 

 and critical key to a few of the most strik- 

 ing questions engaging students of evolu- 

 tionary philosophy. 



Dictionary of the Active Principles of 

 Plants ; Alkaloids ; Bitter Princi- 

 ples ; Glucosides : Their Sources, Na- 

 ture, AND Chemical Characteristics, 

 WITH Tabular Summary, Classification 

 OF Reactions, and Full Botanical and 

 General Indexes. By Charles E. Sohn, 

 r. I. C, r. C. S. London : Balli^re, Tin- 

 dall & Cox. Philadelphia: J. B. Lip- 

 pincott Company, 1894. Pp. vii-f 194. 

 Price, $3. 



The present work treats of nearly six 

 hundred alkaloids, glucosides, and bitter prin- 

 ciples, and it has been prepared in order 

 that the details relating to these substances, 

 now more or less scattered through chem- 

 ical literature, should be so tabulated that 

 not only a given attribute of any substance 

 shall be readily found, but that there shall 

 be information indicating wherein such a 

 substance differs from, or resembles, another 

 of its class. 



The work is arranged in three parts : The 

 first groups together the constituents of one 

 plant or of a number of botanically or chem- 



ically allied plants, following as far as possi- 

 ble an alphabetical order. The second part 

 consists of a tabular summary designed for 

 ready reference as well as for contrasting 

 one compound with another for analytical 

 purposes. The third part is a classification 

 of reactions for the special use of analysts. 



There is a complete botanical as well as 

 a general index to the volume. It is likely 

 to prove a convenient work for the pharma- 

 cologist as well as the chemist. 



A Treatise on Elementary Hydrostatics 

 has been prepared by John A. Greaves (Mac- 

 millan & Co., New York, $1.10) with the 

 purpose of treating the subject as fully as 

 possible without using the calculus ; but 

 alternative proofs have been given Avhere 

 the calculus enables us either to obtain the 

 results more easily or to express them more 

 concisely. Having shown that solids may be 

 classified according to their behavior under 

 the action of forces, the author deduces the 

 definition of a fluid from the characteristic 

 behavior of all substances which we recog- 

 nize as fluids. The special chapter headings 

 are the Properties of Fluids, General Theo- 

 ries relating to Pressure, Center of Pressure, 

 Floating Bodies, The Determination of Spe- 

 cific Gravity, Gases, Hydrostatic Machines, 

 and Capillarity. In the last chapter it is 

 shown from experiments that the energy of a 

 material system depends partly on the extent 

 of the surfaces separating the different sub- 

 stances. On the assumption of the existence 

 of this surface energy, several well-known 

 capillary phenomena are deduced. 



For some time past it has seemed to G. 

 A. T. Middlcton that a concise work upon 

 land surveying, in which modern instruments 

 and modern methods of working were de- 

 scribed, would be welcomed by many. The 

 result has been the production of a small 

 volume on Surveying and Snrveyinff Instru- 

 ments (Macmillan & Co., New York, $1.25), 

 the substance of which has already appeared 

 in a technical journal. It includes chapters 

 on Surveys with Chain only. Obstructions in 

 Chain-line and Right-angle Instruments, The 

 Uses of the Level, Various Forms of Level 

 and their Adjustments, The Uses of Angle- 

 measuring Instruments, The Theodolite and 

 other Angle-measuring Instruments, and In- 

 struments for ascertaining Distances. 



