January 9, 1885.] 



SCIENCE. 



37 



kept permanently closed, or are protected by 

 ante-chambers ; and those of some marsh-plants 

 cannot close at all. In sunn}' places the air in 

 the intercellular spaces is in motion, and may 

 be observed passing out by the stomata. Dur- 

 ing the life of the plant, two maxima of trans- 

 piration occur: (1) in youth, the air passing 

 through the soft cuticle ; (2) in adult life, when 

 it passes by the stomata. 



The suggestion of Sachs, that the narrow- 

 ness of the cells of autumn wood of trees re- 

 sults from tension, is unsatisfactory, because 

 the change from broad to narrow cells is sud- 

 den, and the tension upon the young wood is 

 nearly the same in autumn as in spring. How 

 the difference is caused is not known ; but it 

 benefits the tree by affording wide channels 

 for a plentiful supply of water for the opening- 

 leaves of spring and for the excessive trans- 

 piration of summer, and, on the other hand, by 

 providing thickness and strength to meet the 

 stress of winter. G. Macloskie. 



TROWBRIDGE'S PHYSICS. 



All who are interested in the improvement 

 of elementary science-teaching must regard 

 with no little interest the announcement that a 

 physicist of Professor Trowbridge's deservedly 

 high reputation and great experience has taken 

 time to prepare a text-book in physics for sec- 

 ondary schools. ' The new physics ' is cer- 

 tain 1}* not of the common type of text-books, 

 and it will be generally welcomed as, in many 

 respects, a new departure. 



Exercises in measurement occur from the 

 beginning, and the student is shown the im- 

 portance of ' finding out things for himself at 

 an early stage. The book is rich in sugges- 

 tions concerning the construction and use of 

 simple forms of apparatus, by means of which 

 important physical constants may be deter- 

 mined with some precision. For linear meas- 

 urement such instruments as the vernier, the 

 spherometer, the cathetometer, and the micro- 

 scope with cobweb micrometer eye-piece, which 

 are often among the more expensive appliances 

 of a physical laboratory, are described, and 

 their construction so planned as to tempt any 

 enterprising high-school teacher to undertake 

 their manufacture. Several ingenious methods 

 of measuring small intervals of time are intro- 

 duced, and most of them are so simple that 

 their value can be tested at little expense. By 

 means of these methods the laws of motion 

 are investigated experimentally : in fact, the 



The new physics. By John Trowriudoe. 

 Appleton, 1884. V.) - L 367 p. 12°. 



Now York, 



attempt is made to discover what these laws 

 are, and not merely to verify them. The stu- 

 dent is taught how to construct galvanometers 

 and electrometers, and how to use them in elec- 

 trical measurement. In short, what may be 

 termed the laboratory method of teaching ele- 

 mentary physics is adopted by the author with- 

 out reserve. 



But it is a great disappointment to find a 

 book containing so much that is fresh and 

 original so marred by errors, man}* of which 

 are really serious. The laudable attempt has 

 been made to put the student in possession of 

 certain principles of prime importance which 

 are generally to be found only in the college 

 text-book, and not always there. In the dis- 

 cussion of some of these, mistakes of consid- 

 erable magnitude, and statements that are very 

 misleading, have unfortunately found their way 

 into the text. Of these, some of the most 

 serious are to be found in the chapter on mo- 

 ments of inertia. In attempting to calculate, 

 without involving the element of time, the 

 force with which a steel spring strikes a pen- 

 dulum ball, some inconsistent and extraordi- 

 nary equations are produced. A little further 

 on the reader will be astonished to find it de- 

 monstrated ( ?) that in a lever the products of 

 each force by the square of its distance from 

 the fulcrum are equal ; and on this proposition 

 the principle of moments of inertia is » allowed 

 to rest. The statement is also made that the 

 radius of gyration is the length of the equiva- 

 lent simple pendulum ■ and this error permeates 

 the whole treatment of simple and compound 

 pendulums. In the definition and discussion 

 of equipotentiai surfaces the false assumption 

 is made that force is constant over such a sur- 

 face. Preliminary to the consideration of the 

 work done by an electric current will be found 

 a brief discussion of the dimensions of force 

 and work, which is obscure and misleading. 



There will be considerable difference of 

 opinion about the propriety of inserting in an 

 elementary text-book such matter as the de- 

 termination of the value of the ohm in absolute 

 units, the measure of the horizontal compo- 

 nent of the earth's magnetism, and the meas- 

 ure of electromotive force by the ' throw ' of a 

 galvanometer-needle. 



The book is extremely suggestive, and will 

 be found of great use in the hands of the 

 enthusiastic teacher. A second edition will 

 doubtless be free from the numerous mistakes 

 of the present, which can hardly be regarded 

 as a safe guide to one not already tolerably 

 familiar with the underlying principles of the 

 ' new physics.' 



