NATURE 



245 



THURSDAY, JULY 29, 1875 



PRACTICAL PHYSICS 



WE propose in the present article to carry out the 

 intention expressed in a former number (vol. 

 xii. p. 206) of giving fuller details of the practical in- 

 struction in physics, which forms a part of the summer 

 course of instruction given to science teachers by the 

 Science and Art Department. The teaching of prac- 

 tical physics presents several difficulties, which have 

 no doubt largely militated against its general intro- 

 duction into the course of scientific education. It 

 has not yet been systematised. Unlike practical che- 

 mistry one cannot select a practical text-book on 

 physics and give it to the students ; for such text-books 

 do not yet exist in English. We are not forgetting the 

 translation of Weinhold's Experimental Physics, which 

 we lately reviewed in these columns ; but that book is 

 unsuitable for most students owing to its unwieldy size 

 and high price. 



Even if works on practical physics were at hand, 

 another difficulty is encountered in the costly nature of 

 the apparatus involved in studying physics. This no doubt 

 is one of the main difficulties that the teacher has to over- 

 come, and in this respect physics differs widely from che- 

 mistry, for it is out of the question to provide a complete 

 set of physical apparatus for every two or three students. 

 To meet this difficulty' one may distribute diff"erent in- 

 struments among the students and allow them in turn 

 thoroughly to master what is put before them. This plan 

 might do for a small class, the members of which could 

 use their fingers already. But it is at best an unsatis- 

 factory method, for it leaves the student completely at sea 

 directly he begins to communicate the instruction he has 

 received, unless he can purchase what he has been in the 

 habit of using, and this is not often within his means to 

 do. Another course is first to teach the students how to 

 make simple apparatus for themselves, and then to show 

 them how to use it. The advantages of this plan are 

 apparent. Students unaccustomed to manipulation find 

 to their astonishment, when they begin, that all their 

 fingers have turned into thumbs, and are amazed at their 

 clumsiness and stupidity. Very soon, however, fingers 

 begin to reappear, and the first successful piece of appa- 

 ratus that is made gives them a confidence in themselves 

 which they had thought impossible to attain. The plea- 

 sure of having made an instrument is increased a hundred- 

 fold when it is found that by their own handiwork they 

 may verify some of the more important laws in physics ; 

 or make physical determinations, which before they would 

 have considered it presumption to attempt, even with 

 ready purchased apparatus. In order to carry out this 

 plan successfully, minutely detailed instructions must be 

 given to each student concerning the construction of 

 the apparatus he has to make, and it is moreover obvious 

 that the instruments should not take too long to make, 

 and that the first trials should be with the simplest appa- 

 ratus possible. 



Let us now look at the science teachers at work at 

 South Kensington. Each one has given to him a page 

 of printed instructions for the day's work. These instruc- 

 VoL. XII.— No. 300 



tions have grown up within the last few years under the 

 direction of those who have been associated with Dr. 

 Guthrie in this undertaking, namely. Professors G. C. 

 Foster and W. F. Barrett, together with the valuable aid 

 of Mr. W. J. Wilson. 



In the teaching of Practical Physics perhaps no subject 

 lends itself more readily to practical work than Electricity 

 and Magnetism ; and as nearly every science student has 

 had some little practice in this direction, this branch of 

 physics commends itself as best fitted to begin with. 



The first day's work on Electricity and Magnetism 

 commences with the construction of simple electrical 

 apparatus, as for example "Make a glass tube for 

 electrical excitation ; " then comes what to do in the way 

 of cutting the tube and closing the ends. This intro- 

 duces some to their first experience with the blow-pipe 

 and the manipulation of glass, in which they rapidly 

 gain courage and proficiency. 



After this they are told to make a balanced glass tube 

 as follows : — 



" Glass tube about 12 inches X | inch. Clean and dry 

 inside, close and round one end, nearly close other end. 

 Balance on edge of triangular file, mark centre with file. 

 Soften one side of tube at centre with Bunsen burner, 

 push in side with point so as to make conical cap. Avoid 

 having file scratch at apex of cap." 



Rubbers, pith balls, proof- planes are made, and the 

 fundamental laws of electricity are tried before the day is 

 over. Next day a gold leaf electroscope has to be made, 

 and some capital instruments of this kind are turned out. 

 The insulation of these electroscopes is so high that we 

 have seen them retain a charge for an hour or more when 

 the body of the instrument was standing in water. The 

 secret of the insulation consists in using clean flake 

 shellac ; a little of this substance is melted in the hole 

 through which the wire stem of the instrument has to 

 pass, the stem is then warmed and pushed through the 

 shellac so as to leave about a quarter of an inch thickness 

 of shellac all round the wire. Without attempting to follow 

 each day's work, we notice in passing that the distribu- 

 tion of electricity is tried by using card-board cones and 

 cylinders covered with gilt paper, a Leyden jar with 

 movable coatings is constructed, an electrophorus is 

 made and various experiments tried with it, and even a 

 Thomson's quadrant electrometer is among the more 

 ambitious pieces of apparatus that are attempted. 



Omitting Magnetism, which is not so fully developed 

 as the other subjects, we come to Current Electricity. 

 One of the first things that has now to be made is an 

 astatic galvanometer, which occupies the greater part of 

 one day's work. This instrument works so well, that for 

 the sake of other science students we quote the following 

 instructions for making it : — 



" Wind about 50 feet of fine covered copper wire on 

 wood block ; remove wood ; secure coil by tying with 

 thread ; insulate and stiffen coil by soaking with melted 

 paraffin or shellac varnish. Make another similar coil ; 

 fix the two coils side by side on round wood block, leaving 

 about \ inch space between them and soldering two of 

 the free ends of coils together so as to make one con- 

 tinuous coil. Solder other two ends of wire to binding 

 screws fixed about \ inch from edge of block. Lead ends 

 of the wire also into two little hollows cut in wood block 

 by side of binding screws, so that these depressions may 

 serve as mercury cups ; they are convenient for shunting 

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