August 5, 1880] 



NATURE 



321 



more important facts and laws of the physical sciences 

 can be illustrated and explained by the help of experi- 

 ments made without special or expensive apparatus, and 

 requiring only the familiar objects of common hfe for 

 their performance. The greatest exponents of popular 

 science — and amongst them notably Faraday — delighted 

 in impromptu devices of this kind. It is indeed sur- 

 prising how throughout the whole range of natural philo- 

 sophy the hand of the master can turn to account the 

 very simplest and rudest of apparatus. A silver spoon, a 

 pair of spectacle lenses, a tumbler of water, and a few 

 sheets of paper suffice to illustrate half the laws of geo- 

 metrical optics. A few pieces of sealing-wax, some 

 flannel, silk, writing paper, pins, and glass tumblers will 

 carry the clever experimenter a long way into the pheno- 

 mena of electricity. These are things which any person 

 can procure, and which any person can be taught to use. 

 But their right use depends on the possession of accurate 



scientific knowledge and a clear understanding of luhat 

 the various experiments are to prove. In fact the art of 

 experiment and the science of inductive reasoning are the 

 essential qualifications necessary to make Physics -without 

 apparatus profitable. 



The short series of papers which it is now proposed to 

 publish in Nature under the title of Physics without 

 apparatus will deal with some of the more important 

 and interesting of these simple matters of experiment. 

 The subject of them has been more immediately suggested 

 by the publication in our contemporary. La Nature, of a 

 kindred series of articles by Mons. G. Tissandier, from 

 which a number of the illustrations we present to cm- 

 readers are taken. The matter of the present series is 

 however new. 



Amongst the simple mechanical laws with which a 

 beginner in physics must acquaint himself is that com- 

 monly referred to as the lavj of inertia, which is, however. 



very often so imperfectly expressed as to be misappre- 

 hended.^ It requires force to move matter, not because 

 matter is inherently lazy or sluggish, but because it 

 possesses mass. The greater the mass of matter in a 

 ball, the harder work is it to send it rolling. Force 

 is also required to stop matter that is moving, the reason 

 again being that a mass moving under the impulse of an 

 impressed force possesses a certain moving energy which 

 cannot be at once reduced to nothing. In either case — 

 either to move a mass or to alter the motion of a mass — 

 force must be employed and energy expended. Of this 

 law of inertia many examples might be given : and 

 there are many curious facts which this law serves to 

 explain. Some of the most striking of these are those 

 in which the effect of sudden forces is difterent from that 

 which might have been expected. In Fig. i we give an 

 illustration of an experiment of this nature. A wooden 

 rod— say a broomstick— has a couple of needles fixed 



into its ends, and it is then supported upon two wine- 

 glasses resting upon two chairs. If a heavy poker is 

 now brought down very violently upon the middle of the 

 stick it will break in tno without the needles or the 

 glasses being broken. A feeble or indecisive blow will 

 fail to do this, and will break the glasses or the needles, 

 or both. Here the moving energy of the heavy mass, 

 the po'.ier, is suddenly transferred to the middle of the 

 stick, so suddenly that it is broken asunder before the 

 thrust has time to reach the fragile supports. 



Another simple experiment on inertia is equally instruc- 

 tive. Lay any ordinary visiting-card upon the knuckle, 

 or upon the top of an inkstand or other convenient sup- 

 port. On the card place a brass weight, or a spool 

 of thread, or any other small heavy object. Now flip 

 away the card with the finger and thumb ; it will fly out, 

 leaving the heavy object where it was. In the same way 

 if a dozen draughtaren are piled up one upon another 



