Sepi. 1 6, iSSo] 



NA TURE 



of special instruments of an expensive character. Only 

 the first and simplest of the elementaiy phenomena of the 

 science can be shown without apparatus. Yet even here 

 the rudest means suffice in the hand of the master to 

 produce the desired ends. 



In his lessons on Frictional Electricity, delivered to 

 juvenile audiences at the Royal Institution, Prof. Tyndall 

 has shown in his unrivalled way how with the commonest 

 objects, tumblers, egg-cups, needles, sealing-wax, pewter- 

 pots, eggs, apples, and carrots, may lend themselves to 

 produce the sparks, the shocks, the movements of attrac- 

 tion and repulsion which are more commonly obtained by 

 the use of large and expensive electrical machmes. No 

 doubt these lessons — masterly examples of elementary 

 science teaching — are familiar to many of the readers of 

 " Physics without Apparatus." To the science teacher 

 they are an indispensable primer of instructions how to 

 impress common objects into the service of science. The 

 only matter for regret is that they stop so far short of the 



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Fig. I 6. 



entire subject, and do not touch the kindred branches of 

 voltaic electricity or magnetism. 



The experiments we lay to-day before our readers are 

 mere repetitions of ordinary lecture experiments, but 

 require no apparatus of a technical kind for their per- 

 formance. To show the attractions and repulsions due 

 to electrification requires only the appliances depicted in 

 Fig. i6. A stick of sealing-wax rubbed briskly through 

 a dry warm piece of cloth or flannel suffices as a source 

 of electricity. A small light ball cut out of pith or cork 

 is attached by a drop of sealing-wax to a silk thread and 

 thus suspended to any suitable support. It is first 

 attracted toward the electrified stick of wax ; and then 

 repelled when by contact it has received a portion of the 

 charge. The repulsion is not very easy to show if the 

 ball is not exceedingly light. For this purpose a small 

 feather, or bit of down out of a pillow, answers far better. 

 A support from which to hang it may be improvised out 

 of a penholder and a couple of books. The electricity 

 excited on the wax by friction with a woollen fabric is of 

 the negative kind. Positive electricity is no less easily 



obtained from a warm glass tumbler by exciting it ■( 

 warm and dry silk handkerchief. And, if both 



sources arc at hand the further experiment may be 



of charging the feather with either kind of electricity and 

 then showing that though it is then repelled by electricity 



of the same kind, the opposite kind of electricity attracts 

 it. The mutual repulsion of two similarly electrified 

 bodies is beautifully shown by means of two silk ribbons, 



