i6o 



NA TURE 



\yuly 2, 1874 



has quite descended below the level of that quality of 

 work which needs the distinguishing encouragement 

 afforded by the publication of the results obtained in the 

 " Transactions" of any learned Society. 



PICKERING'S "PHYSICAL MANIPULATION" 

 Ekmcnis of Physical Manipulation. By Edward C- 

 Pickering, Phayer Professor of Physics in the Massa- 

 chusetts Institute of Technology. Part 1. (London : 

 Macmillan & Co., 1874.) 

 ■T^O write a satisfactory text-book for students in phy- 

 -!- sical laboratories is a task beset with difficulties ; 

 and although Prof. Pickering has had the advantage 

 of no small experience and judgment in the composition 

 of the work the title of which is given above, we do not think 

 that he has entirely overcome them. 



There can be little doubt that oral teaching is that 

 which is best suited to students who are beginning ex- 

 perimental work of any sort, and that as much may often 

 be learnt in five minutes by seeing another perform an 

 experiment as would be acquired in as many hours with 

 the aid of a book alone to explain the construction and 

 use of the apparatus ; and Prof. Pickering is therefore 

 right in aiming at supplementing rather than superseding 

 the efforts of an instructor. 



The work is divided into sections, each of which relates 

 to one or more experiments, and comprises two parts, the 

 first of which, entitled "Apparatus," gives a description 

 of the instrument required, and is designed to aid the 

 instructor in preparing the laboratory for the class, while 

 the second, headed " Experiment," explains in detail to 

 the student what he is to do. 



The subjects treated of in the first volume, the only one 

 at present published, are Mechanics, Sound, and Light, 

 an arrangement that does not agree with the order in 

 which they would probably be studied in the laboratory, 

 as the elementary parts of heat ought certainly to be 

 taken with mechanics ; but the plan adopted has the 

 advantage that heat and electricity, the subjects in 

 which tables are most required for reference, will be 

 placed together in the second volume, in which also, we 

 presume, sets of tables will be included among the 

 "matters of general interest to the physicist" that are 

 promised in the preface. 



Apart, however, from any detailed criticism, we 

 must notice the important preliminary question, how 

 far a work of this sort is likely to fulfil the object 

 with which it is written, of enabling an instructor to 

 superintend a larger class than he could otherwise 

 attend to at once ? The members of the class, ac- 

 cording to the method of instruction pursued in the 

 Massachusett's Institute, and described in the preface, are 

 not informed precisely whatexperimcnts will be allotted to 

 them until they enter the laboratory, and as such is the 

 plan probably generally adopted where the number of 

 pupils is large, it is absolutely necessary for the instructor 

 to have at hand, either in a text-book or in manuscript, 

 short papers on the theory of the different experi- 

 ments. We do not, however, feel sure that the descrip- 

 tions of apparatus and methods of performing experi- 

 ments will prove so valuable as might at first sight appear 



probable. The instruments required for physical work are 

 often so costly as to make constant supervision necessary 

 over those who are not accustomed to them, and their con- 

 struction is so various, at all events in minor particulars, 

 that directions for their use which might be all that could 

 be desired in one laboratory might be misleading in 

 another. Another difficulty arises in describing experi- 

 mental proofs of the simpler laws of Mechanics and Physics 

 which do not require elaborate apparatus for their exhi- 

 bition, as a choice has often to be made between several 

 different methods, an account of all of which would make 

 the text-book unwieldy in bulk, while the omission of any 

 is apt to make it less useful in laboratories other than 

 that for which it was originally intended. The selection 

 of experiments of this sort must in great measure depend 

 upon the time the pupil is able to devote to the study of 

 physics, the objects he has in view in pursuing it, and in 

 many cases upon his knowledge of mathematics ; and we 

 regret that Prof. Pickering seems occasionally to have 

 chosen those which are likely to give the best numerical 

 results, in preference to others which, depending more 

 upon skill, are not indeed so suitable for the exact verifica- 

 tions of physical laws, but have a greater educational 

 value in improving the powers of observation. 



The method selected, for instance, for illustrating the 

 laws of falling bodies is that of suspending a ball to a 

 spring, which, when the connecting thread is severed and 

 the ball allowed to fall, completes a galvanic circuit in 

 which a chronographis included, and which is again broken 

 by the impact of the ball on a plate placed below to receive 

 it. This method is well adapted to show the relation be- 

 tween the time of falling from rest and the distance 

 traversed ; but Attwood's machine, of which no account 

 is given, illustrates the fundamental laws of dynamics 

 much more completely, is capable, if fitted with proper 

 electric arrangements, of giving extremely good results, 

 and is better suited for use by the pupil, as in our opinion 

 all such instruments ought at first to be used, with some 

 means of measuring time, such as the stop-watch, water- 

 clock, or metronome, dependent upon skill, and not upon 

 a purely mechanical arrangement. 



Some of the experiments described are avowedly given 

 as a preparation to those who may have to give lectures 

 on physics, and others are, we presume, inserted with the 

 same intention, as it would hardly be necessary for those 

 possessing that " moderate familiarity with the general 

 principles of physics " which " the class is supposed to 

 have previously attained" to spend time over the experi- 

 mental proofs given of the laws of the composition of 

 forces, or the equality of the angles of incidence and 

 reflection. 



The earlier pages of the book are devoted to general 

 remarks on physical measurements, and on methods of 

 working up the results of experiments, and they will prove 

 very useful. 



The knowledge of mathematics assumed throughout is 

 small, and in several instances the line has in this respect 

 been drawn too tightly, no account being given of the 

 method of determining the coefficient of torsion by 

 means of the torsion pendulum, or of the determination 

 of gravity by the reversible pendulum, probably on ac- 

 count of the small amount of rigid dynamics required in 

 these problems. 



