442 THE JOURNAL OF GEOLOGY. 



ing. In this connection, the author points out another error found in 

 many text-books, namely that the oblique course of the winds is due 

 to a lagging behind, as they move from regions of less to those of 

 greater rotary velocity, and, therefore, that winds traveling due east 

 would not be deflected at all. As was clearly shown by Ferrel, many 

 years ago, both the explanation and its corollary are wrong, although 

 they have appeared in many text-books, even of recent date. 



Following the discussion of a competent theory for the general cir- 

 culation of the winds, there is given a systematic account of the dif- 

 ferent members of the circulation, and a classification of winds accord- 

 ing to cause into (i) planetary, (2) terrestrial, (3) continental, (4) land 

 and sea breezes, (5) mountain and valley breezes, (6) cyclones and 

 other storms, (7) eclipse winds, (8) landslide and avalanche blasts, (9) 

 tidal breezes, (10) volcanic storms. 



Chapter X., treating of cyclonic storms and winds, is one of the 

 most interesting and valuable in the book. The tropical cyclones are 

 first considered. The evidence of convectional action in these cyclones 

 is considered, and it is shown that their distribution both in time and 

 place points strongly to the theory that they originate through the 

 overturning of great masses of air, due to unequal heating. But it is 

 clearly pointed out to the pupil that it has not yet been directly shown 

 that the temperature of the cyclonic mass is higher than that of the 

 surrounding atmosphere at corresponding altitudes, a condition which, 

 of course, must be satisfied before convection can take place. If this 

 shall, hereafter, be shown not to be the case, the convectional theory 

 will have to be abandoned. 



In points like this. Prof. Davis' book is particularly good, for, all 

 along, he has stated clearly not only what is certainly known, what is 

 probable, and what is doubtful, but also what is not known. This 

 prevents the student from forming misconceptions of the subject, or 

 dropping into loose habits of thought. 



The extra-tropical cyclones are closely compared with the tropical 

 cyclones, and their points of likeness and difference shown. Two 

 theories for their origin are discussed, and lines are indicated along 

 which the rival theories may, some day, be tested, but here again, the 

 fact is emphasized that much is not yet known, and that positive didactic 

 statements are to be avoided. 



Space will not permit even a brief mention of many other points 

 to which we should like to call attention. The subjects of thunderstorms, 



