March 1, 1899.] 



KNOWLEDGE, 



63 



combat, may have ensued. But the important point for 

 our consideration is this, we may again assume that the 

 commodity of which more was first demanded was a food- 

 stufif. Oliver Twist's demand was only novel in a relative 

 sense, while that which we are considering is novel from 

 hypothesis, but its meaning, we need not hesitate to say, 

 was relative. More, or the synonymous expression was 

 used. 



Leaving for the moment this distinction between relative 

 and absolute measurements, we come to another point of 

 view, and ask, " What was the physical quantity which 

 first became an article of barter ? " 



As regards the transaction alluded to, the answer would 

 appear to be weight. But that is a popular error, if the 

 purchase had to be conveyed any distance the weight 

 would be a distinct nuisance. This graphic distinction 

 between weight and mass is, I think, due to Prof. Olaus 

 Henrici. A little reflection shows ua that the physical 

 quantity first purchased or bargained for is more than 

 likely to have been muscular energy. The ability to wield 

 a primitive spade must have been early in demand, like- 

 wise the power to manipulate a club. 



Now let us contrast this state of things with that existing 

 at present. The great distinction lies in that our measure- 

 , menta are absolute, or referred to some recognized system 

 of units. Following out the same train of ideas, we find 

 that the commodity perhaps most marketable now is 

 energy, or the means of producing energy. There is, how- 

 ever, one marked difference. With the growth of mental 

 energy, muscular energy is being largely superseded by 

 mechanical and physical energy. Gas and coal are 

 purchased, because heat, light, or energy, are required, 

 whUe electrical energy is actually sold at so much per unit. 

 As it is this latter commodity with which we are to concern 

 ourselves, it may not be out of place to note the following 

 facts. 



The so-called electric current is never sold. It flows 

 through the consumer's apparatus, and, under ordinary 

 conditions, every milliampere is scrupulously returned by 

 him, if unconsciously. Nor is electrical pressure sold. It 

 may be regarded as potential energy. 



To bring these points out more clearly, let us consider 

 a parallel case. The owner of a large pond, situated on 

 the top of a hill, could never find a purchaser for the 

 pressure which that volume of water exercised on the sides 

 and bottom of the pond. But, if he were to let the water 

 flow down the hill, to drive mills, turbines, and so on, it 

 would become a distinct source of income to him, while at 

 the same time he would not be justified in charging any- 

 thing for the water if it all flowed into a lake of his own 

 at the bottom of the hill. It is then kinetic energy which 

 appears to be the article in demand. 



I am to some extent ashamed of having used the expres- 

 sion potential energy here, though it serves so well to 

 illustrate the point under discussion. What I would imply 

 is, that if we define potential energy as the energy which 

 a body has on account of its position, and kinetic energy 

 as the energy derived from its motion, it is quite obvious 

 that the difference is only one of degree. ■' If the potential 

 energy of a body, or system, be increased, it will, when 

 that increase is sufiicient, be converted, or partially con- 

 verted, into kinetic energy. 



Returning to the consideration of electrical energy, and 

 its measurement, we find that the commercial measure- 

 ment of electricity is on a far more reasonable basis than 



* I am well aware that many people, possessing knowledge and 

 wisdom superior to my own, have no hesitation in accepting potential 

 energy as energy differing in qualify from kinetic energy. Yet I 

 would ask them to reconsider this doctrine. — H. B. L. 



the commercial measurement of almost any other article 

 of commerce. By reasonable I mean practical, and, in 

 consequence, scientific. 



But let us examine this claim which I have put forward. 

 Bread is sold by weight. No one ever required heavy 

 bread yet. The play upon words is inevitable, and like so 

 much of the inevitable, unfortunate. Bread is purchased 

 because it can support animal life. It by no means 

 follows that four pounds of bread purchased to-day is so 

 well capable of supporting animal life as that which 

 may have been obtained last month. Yet, the weight 

 being the same, the same price is in all probability paid. 

 Here electrical dealings can claim to be on a far more 

 scientific basis than those which refer to " The Staff 

 of Life," because the purchaser pays for that attribute of 

 electricity which he requires, while in the other case he 

 pays for what he does not require. And " electricity is 

 only in its infancy," precocious child! ! Curioualy enough, 

 if the same contrast be made between the rational com- 

 mercial measurement of electricity, and the existing 

 stupid measurements of the very necessaries of life, it 

 will stiU give us the same result, and be entirely favour- 

 able to electricity. It may be urged that it would be 

 " unpractical " to endeavour to gauge the number of 

 units of heat obtainable from a given ton of coals. On 

 the other hand, the use of the word " unpractical " is a 

 distinct misuse in this connection, added to which, one 

 is led to ask, Has any effort been made to render such a 

 system common ? Arrived, then, at the bald statement that 

 the measurement of electrical energy is the direct 

 measurement of what the consumer actually requires, we 

 are in a position to state that this style of measurement 

 is going on autotmiticaUy in millions of places day and 

 night. By comparison with the treatment " meted out " 

 to our infant, most commercial measurements, of the 

 very commonest and most necessary articles, seem to be 

 based on systems that are distinctly in their dotage. A 

 pint of milk is by no means the same thing all the 

 world over, neither is a cubic foot of gas. But a watt is. 

 Let us just in passing define the watt, and next 

 consider how it is measured. A current of one ampere 

 (unit current), propelled by a pressure of one volt (unit 

 pressure), is precisely equal to one watt of electrical 

 energy. But to form a working basis for the charges to 

 be made to consumers, time, of course, comes into the 

 consideration. Hence, the " Board of Trade " unit is 

 ten thousand watt-houra. That is, ten thousand watts 

 supplied for one hour, one watt supplied for ten thousand 

 hours, or any intermediate manner of making up the 

 product, as for the sake of simplicity we confine our- 

 selves to the consideration of whole numbers just 

 now. 



For highly accurate measurements of current strength 

 a silver voltameter is generally made use of, and the 

 calculation is based on the fact that one ampere, flowing 

 for one second, deposits 1-118 milligrammes of silver per 

 second. Fortunately, however, there is a far more rapid 

 method of making current measurements, which, as a 

 natural consequence, is adopted in practice. 



We know that a magnetic needle hung or pivoted with 

 its axis parallel to a conductor will be deflected by the 

 current in that conductor, and this angular deflection is a 

 distinct measure of the current strength, where the force 

 tending to keep the needle in its original position is of 

 uniform magnitude, and the position of the conductor 

 remains unchanged. Instruments, therefore, are made on 

 this principle, then calibrated by comparison of their 

 readings with the results given by a silver voltameter, when 

 the same currents were passing through the two. The 



