160 



KNOWLEDGE 



[Aco. 4, 1882. 



THE RELATION OF EXERCISE TO 

 BRAIN-WORK. 



RECENT nunili^rs of the I^ndon Spectator have coii- 

 tAJiifd verv iiit«^rt sting conimunk-ations on this sub- 

 ject NoHiiiig like a general rule can be evolvod from 

 them, Uxause individual temperament^ employment, and 

 circumstiihoes create an endless variety of cases that no 

 rule could cover. • The more witnesses, however, the 

 greater the ehance thht the inquirer will tind a hint suitable 

 to himself, and it is every one's experience that such hints 

 often dt termiue the happiness of a lifetima The author 

 of "The Duties of Women," a great believer in physical 

 exercise, thinks that it "need not and cannot well bo 

 taken on the same days when the heavy mental work 

 has to-be •done." Mind and body may best bo strained 

 alternately by days or by seasons. Especially docs she hold 

 that every woman should provide for some perspiring 

 exercise — " a natural Turkish bath "—at short intervals. 

 An Oxford man advocates pleasurable change as the chief 

 element of recuperation, more important than the muscular 

 exercise ; for wliich reason he prefers horseback and bicycle 

 riding to walking. His rule is — " One hour of some 

 thoroughly good forin of exercise every day, and every 

 week several additional hours' 'change.' " Another con- 

 tributor has " uniformly found that reducing the diet, and 

 especially avoiding the too free use of heat-producing 

 foods, if not an equivalent for the lack of exercise, 

 at any rate enables one to pursue one's desk-work 

 in comfort, with efficiency, and without harm accruing." 

 No doubt there is sense in all these suggestions, 

 and Bome are w ithin the reach of everyone. We should 

 onrselvrs lay stress on the advantage of a thorough 

 gymnastic training as the basis of all subsequent modes of 

 exercise. 1 he muscular tone of the .system, once established 

 in this way, can be maintained with a minimum of effort 

 and time by the chamber use of clubs, dumb-bells, or even 

 simpler contrivances. The back, the chest, and the ab- 

 dominal organs, which are the chief sutferers from sedentary 

 pursuits, can thus f)e directly addressed in the counter- 

 vailing exercise. If to this can be added a .short lialf- 

 mile run in the open air, the account will generally be 

 found squared daily for any but exhausting mental exer- 

 tion. The rule, Imphlus venter non v^ut studere 

 libenter, is, of course, as good for exercise as for 

 brain-work. Beyond thi.s, it is hazardous to dog- 

 matise. ' Some cannot safely take a long walk on an 

 empty stomach, or before breakfast ; to others, nothing is 

 easier, more exhilarating, or apparently more harmless. 

 Some walkers have only rambling thoughts while on the 

 road ; others do their btat and closest thinking under such 

 circumstances. Rousseau belonged to the latter class : his 

 mind needed the motion of the body to stimulate it to its 

 utmost Yet he was not jaded by this two fold activity, 

 and was, moreover, alive to the passing beauties of the 

 scene : he did not oyerlook the wayside peri wink la With 

 some the morning and daylight hours are best for intellec- 

 tual performance ; others require the silen.-e of the small 

 hours of tlie night Anyone who can order his habits to 

 Buit his idiosyncracies, physical »nd mental, has no excuse 

 for running down from lack of proper exircise or from 

 ovor-exercite. Among all the felicities of Darwin's life, 

 this ability was certainly one of the most enviable and the 

 most profitable for mankind. — From the Nation. 



Bvonnr. the Elkctric Lionr.— A Inrgo ir<.n bnoy wan rtrently 

 towed from tlio Oovermnont workd nt Tompkinsvillo, Hiaton 

 Uaod, to ihe lower bay, wboro it i» to hn used to support an 

 •Icctric light. 



THE AMATEUR ELECTRICIAN. 



KLECTIUCAL JIKASURKMENT.— I. 



IT is only natural that before we attempt to measure a 

 substance, wc should inquire what that substance is. 

 Generally speaking, we can answer such a question. We 

 can say that we have a pound of potatoes, that a potato is 

 a vegetable product, and occupies space. We can see it, 

 feel it, taste it We can say that tlie potato is so many 

 inches in circumference, or that it displaces a greater or 

 less quantity of water. Not so with electricity. It 

 requires no argument to demonstrate that wo can get 

 neither a pound, a pint, or an inch of it. All substances 

 that can be so measured are ponderable, have a definite 

 chemical constitution, and are in many cases visible. 

 Electricity, on the other hand, is invisible, inodorous, 

 tasteless, and imponderable. The weight of a mass of 

 metal, ifcc, is not increased or decreased by charging it 

 with electricity. 



If, then, electricity has neither of the properties by 

 which material substances are measured, we must ascertain 

 what properties pertain to it which are available for ren- 

 dering measurement possible. It is assumed that all aro 

 acquainted with the fundamental differences between force 

 and matter ; that whereas matter embraces everything 

 which has weight, force may bo said to be a condition of 

 that matter, or that which will produce a change in matter. 

 It follows that to measure a force, we can only do so by 

 studying its effects on matter. Thus wo speak of heat as 

 being suflicient to convert ice into water, water into steam, 

 itc. Similarly, wc may measure electricity by its capacity 

 for producing chemical changes, deflecting magnetic needles, 

 generating other forces (light, heat, ttc), and so forth. 



Electricity, then, possessing all the general attributes of 

 those forms of force with the effects of which wo aro well 

 acquainted, we may fairly maintain that it also is embraced 

 in that classilication. To measure this force it is necessary 

 to say first a few words on its production. It is known 

 to most people of general scientific intelligence, that 

 if a piece of glass is rubbed with a piece of flannel, 

 or if two pieces of metal are connected and immersed 

 in acidulated water, an electric current is generated, 

 or if the junction of two pieces of metal is heated, or 

 if a magnet is moved in a coil of wire, we get electri- 

 city. But it would not be difllcult to find that many 

 other changes in the physical world aro accompanied by a 

 more or less active display of electricity. In fact, turn where 

 we may, electricity shows itself, and recent discoveries seem 

 to indicate in no very uncertain sounds that every move- 

 ment, whether it bo of the mass or the particle, whether 

 it be cliemical or physical, is accompanied by a greater or 

 less development of electricity. 



We shall use the ordinary galvanic battery as the 

 method of producing the electricity which we are about to 

 measure. 



'J'he strength of a current varies according to the circuit 

 through which it passes, but the first feature necessary for 

 us to understand is its potential. Potential is that property 

 of electricity which determines itn motion from one point 

 to another. Thus the power it has to overcome resistance, 

 to leap across air in the form of a spark, to burst through 

 the gutta-percha covering of a wire — in fact the power it 

 has to form a current, is its potential. We may compare 

 it to force with which high-pressure steam in a closed 

 vessel persistently endeavours to escape. If two bodies at 

 the same potential be connected with each other by some 

 conducting medium, such as a wire, nothing will occur, 

 but if one be at a higher potential than the other, a 



