422 



SCIENCE. 



[N. S. Vol. XVII. No. 428. 



In a new edition, which ought certainly 

 soon to be demanded, two omissions might be 

 advantageously repaired, by adding accounts 

 of the development of the ear bones and of the 

 pulmonary arteries. 



The defects, of which some examples have 

 been given, can not any of them be regarded 

 as fundamental. Some such defects are in- 

 evitable in a first edition of a text-book deal- 

 ing with a science, like embryology, in which 

 research is so active that almost every week 

 brings important additions to knowledge of 

 the subject. The only part of the work which 

 seems to the reviewer radically inadequate is 

 that on the formation of the germ-layers. 



Professor Mcllurrich's volume will be 

 eagerly welcomed by students and teachers 

 alike, and its special distinction is the thor- 

 ough recognition it displays of the morpho- 

 logically essential aspects of embryology. It 

 ought to exert a wide and helpful influence 

 on the advancement of anatomical science in 

 America. C. S. Minot. 



Field Astronomy for Engineers. By George 



C. CoMSTOCK. jSTew York, Wiley & Sons. 



1902. Pp. x-f 202. Price, $2.50. 



Wiley & Sons have just published an ex- 

 cellent text-book on astronomy written by 

 Professor George 0. Comstock, professor of 

 astronomy in the University of Wisconsin, a 

 text-book which undoubtedly will meet with 

 cordial approval from that body of teachers 

 whose duty it is to teach astronomy in tech- 

 nical schools. Por many years there existed 

 no concise manual of the subject, the teacher 

 being obliged either to use an elaborate 

 treatise like Ohauvenet's, or else employ the 

 unsatisfactory method of presenting the sub- 

 ject entirely by lectures. The present work 

 is the third attempt to supply the deficiency, 

 other similar publications of recent date being 

 those of J. P. Hayford, formerly of Cornell 

 University and now of the U. S. Coast Sur- 

 vey, and of W. W. Campbell, director of the 

 Lick Observatory. 



The peculiarity and advantage of the pres- 

 ent book are that it omits entirely that portion 

 of the astronomical theory and instrumental 

 niceties beyond the needs of engineering stu- 



dents and, on the other hand, lays special 

 stress on the methods by which only siifficient 

 precision is attained to meet engineering re- 

 quirements. This general plan of the author 

 enables him to discuss, and he does it with 

 much skill, the question of the inter-relation 

 of accuracy of results with instrumental 

 manipulation, and should give the student a 

 clear insight into the proper methods and 

 formulse to use on any particular occasion. 

 At the same time the author emphasizes the 

 necessity of methodical computation and in- 

 sists on a habit of checks, so desirable a habit 

 for engineers in all kinds of computations. 

 In some cases it may be necessary to elab- 

 orate verbally some of the theory involved, 

 and to explain, as doubtless the author does 

 to his own classes, much of the instrumental 

 manipulation, so that the book is essentially 

 one -to be used by an instructor whose own 

 astronomical training includes much not in 

 the book; but as this is always, at least theo- 

 retically, the case, it should not stand as a 

 criticism against the book. 



The plan of the book includes, after a dis- 

 cussion of the fundamental concepts of co- 

 ordinates and the transformation of one sys- 

 tem into another and of the various methods 

 of noting them, methods of observation and 

 computation for the determination of time, 

 latitude and azimuth. Each determination is 

 carried out according to the requirements, 

 either roughly, approximately or accurately, 

 in each case modifying the formulae and the 

 use of instruments as required. Por example, 

 for the rough determination of time, use is 

 made of an engineer's transit to observe on 

 Polaris at any instant, the correction to the 

 meridian being given by the use of tables. 

 For the approximate determination, the meth- 

 od given is that of making a series of altitude 

 observations with a sextant on a known star 

 or on the sun when that body is near the 

 prime vertical. Por the accurate determina- 

 tion, the method of double altitudes is ex- 

 plained, and a whole chapter is devoted to 

 discussing the transit instrument with its 

 errors and corrections. In each of these 

 cases, as well as in the similar series for lati- 

 tude and azimuth, the detail of work, the 



