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POPULAR SCIENCE MONTHLY. 



currents, air movements, depth of water, etc., render these theories prac- 

 tically valueless for use in tidal calculations. 



In the following section Dr. Draper shows how, by means of Lord Kel- 

 vin's "harmonic analysis," which separates the tide-generating forces of 

 each kind into a number of ideal components, results of practical value 

 are obtained. In Chapter XIII a very ingenious instrument for tide pre- 

 diction which has been in use for some time by the Indian Government 

 is described. The recording part of the machine is simply a paper-wound 

 drum, on which a pencil point makes a graphic record. When the tides of 

 a given port are desired, it is only necessary to set the instrument accord- 

 ing to the tidal components, obtained by harmonic analysis and the time 

 chosen for the beginning of the tide table, and then start it at the proper 

 moment. It takes about four hours to run off the tidal curve for a year. 

 This curve is then measured, and the year's tide table readily made out. 

 Dr. Darwin informs us that a very similar instrument is now in course of 

 construction for the United States Government. The remainder of the 

 work consists of a more detailed discussion of the various disturbing influ- 

 ences which interfere with the simplicity of tidal movements— displace- 

 ment of the earth's axis, earthquakes, etc , a long discussion of tidal fric- 

 tion, a study of the laws of rotating liquid masses, the nebular hypothesis, 

 and finally a chapter on Saturn's rings. The text in many places will be 

 found difficult to understand by the general reader, despite the author's 

 efforts to fully and simply explain every point, and it seems questionable 

 whether a thorough discussion of tidal phenomena can be made simple 

 enough for the layman's comprehension. The volume can not be read by 

 any one, however, without instruction, and is much the best general discus- 

 sion of tidal phenomena which we have seen. 



GENEKAL NOTICES. 



The Elementary Zoology of Frank E. 

 Beddard * contains an account of a few 

 types selected from the chief groups of the 

 animal kingdom, followed and accompanied 

 by a consideration of some of the more gen- 

 eral conclusions of biology. A type system 

 ha3 to be used, but the author has endeav- 

 ored to obviate the great fault of that meth- 

 od — the liability of the students conceiving 

 that the characters of the species selected 

 for description are distinctive of a wider as- 

 semblage of forms — by emphasizing here 

 and there the differences between allied 

 groups. The question arises whether to be- 

 gin with the higher forms and go down to 

 the lower, which some authorities believe to 

 be the course easier of comprehension by 

 the student, or to follow the inverse method. 

 The author prefers to begin with the lower 



* Elementary ZoOlogy. By Frank E. Bed- 

 dard. New York: Longmans, Green & Co. Pp. 

 208. Price, 90 cents. 



forms and gradually work to the higher as 

 the course having the undoubted advantage 

 of presenting the facts in a logical sequence. 

 He accordingly begins with the amoeba and 

 proceeds upward. The treatment is simple 

 and lucid. Novelty has not been sought in 

 the illustrations, though there are several 

 new ones, but selections have been made 

 from the best already drawn. 



An Introductory Logic * grew out of the 

 lectures of the author, Prof. J. E. Creighton, 

 to undergraduate classes in Cornell Univer- 

 sity ; is intended primarily as a text-book 

 for students, and aims at being both prac- 

 tical and theoretical. The broad view is 

 taken in the definition of the subject that 

 logic is the science of thought, or the science 

 that investigates the process of thinking; 

 and the author expresses himself convinced 



* An Introductory Logic. By James Edwin 

 Creighton. New York: The Macmillan Company, 

 pp. 392. $1.10. 



