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SCIENCE 



[N. S. Vol. XXX. No. 782 



are historical details not easily attainable else- 

 where. There is a valuable annotated list of 

 minerals and an excellent bibliography. There 

 is some need for the author to take greater 

 care to attain a form of expression which may 

 be grasped by those not necessarily widely 

 read in the science. Unusual words such as 

 femic, salic, crenitic and the like might best 

 be omitted. In the stratigraphical table, page 

 5, if Carboniferous is replaced by Carbonic, 

 why not use also Cambric, Siluric, Devonic 

 and Cretacic. In the treatment of the stra- 

 tigraphy of Manhattan Island, it is far simpler 

 and clearer to take up the Fordham gneiss, 

 the Inwood limestone and the Manhattan 

 schist, than to treat merely of gneiss, lime- 

 stone and schist, with minor varieties. If, 

 when a fourth edition is called for, the author 

 will place himself in the attitude of a reader 

 not of profound attainments in geology and, 

 thus grasping his or her point of view, will 

 put the facts of the local strata in simple and 

 clear language, and will add an index, a work 

 already serviceable and of value will be made 

 still more so. J. F. Kemp 



An Elementary Treatment of the Theory of 

 Spinning Tops and Gyroscopic Motion. By 

 Harold Crabtree. Pp. xii + 140. New 

 York, Longmans, Green & Co. 1909. 

 This is a very satisfactory book for one who 

 wishes to gain a clear understanding of 

 gyroscopic action. It contains a good discus- 

 sion of Schlick's method of steadying vessels 

 at sea and of Brennan's gyroscopic mechanism 

 for balancing a monorail car. 



The introductory chapter describes a num- 

 ber of curious and interesting forms of tops 

 and gyroscopes. Chapter I. discusses rotation 

 about a fixed axis. Chapter II. discusses pre- 

 cession and Chapter III. is a discussion of the 

 phenomena described in the introductory 

 chapter. 



The starting of precession and gyroscope 

 oscillations are discussed in Chapter IV., and 

 the remainder of the book. Chapters V., VI., 

 VII., VIII. and IX., discuss the more elaborate 

 aspects of the theory of gyroscopic action. 

 The curious behavior of the stone imple- 



ment known as the celt which is described on 

 pages 7 and 54 may be observed with an ordi- 

 nary pocket-knife with a rounded back. When 

 such a knife is twirled on a smooth table the 

 reaction of the table due to its vibratory mo- 

 tion causes its direction of spin to be reversed 

 and if the knife is set rocking about a hori- 

 zontal axis the reaction of the table due to 

 the vibratory motion produces a slight spin 

 about a vertical axis. 



Altogether the book is a welcome and val- 

 uable addition to the literature of rotatory 

 motion. 



W. S. Franklin 



SPECIAL ARTICLES 



A SIMPLE CLOUD APPARATUS 



The celebrated experiment on the produc- 

 tion of clouds by C. T. R. Wilson forms an 

 instructive lecture table demonstration. This 

 need not necessarily be a difficult experiment. 

 It is common observation that clouds of 

 greater or less density are often seen upon the 

 first few strokes of the pump when evacuating 

 a vessel containing some moisture. The appa- 

 ratus as Wilson constructed it was of neces- 

 sity rather elaborate. That it may be of ex- 

 ceedingly simple and inexpensive construction 

 and yet capable of giving quantitative re- 

 sults of a fair degree of accuracy is the object 

 of this paper. 



The apparatus consists of a glass bulb 

 having two openings. To one, the larger, is 

 attached a stiff rubber bulb, to the other a 

 nipple for the introduction of the gases, etc., 

 to be investigated. For qualitative results the 

 glass vessel is blown in the form of a hooded 

 bulb B, as shown in Fig. 1. This bulb should 

 have a volume of about 75 c.c, while the hand 

 bulb HB may be the stiff bulb that comes with 

 an hydrometer syringe for testing electrolytes. 

 The volume of this bulb should be about 250 

 c.c. The nipple n is closed by a rubber tube 

 and a screw pinch-cock at p. It is well to in- 

 sert a short glass tube extension beyond p. 

 To operate, draw into the bulb B two or three 

 cubic centimeters of water. This will be 

 caught by the annulus or trough in B, thus 

 keeping the gas in the bulb in contact with 



