July 14, 1892] 



NA TURE 



25 



definition now becomes an inexact truism asserting that 

 the Earth attracts W lbs. with a force of W pounds, and 

 inexact, because it neglects the discount in, ^ due to the 

 rotation of the Earth ; and to say that " the weight of 

 a body is the force with which it is attracted by the 

 Earth " conveys no additional information. 



Having introduced the word mass, primarily as a 

 mere abbreviation in printing, and having subsequently 

 changed the unit of mass so as to make the mass the 

 same as the weight, the theorist is now trying to dislodge 

 the word weight from its primary meaning, which it has 

 possessed for thousands of years, as meaning the quantity 

 of matter in a body, and is trying to degrade it into a sub- 

 sidiary position, to express a mere secondary idea, the 

 attraction of gravity ; and that only on the surface of the 

 earth, and even then not clearly defined. 



We might as well define the pound sterling by its 

 purchasing power in any locality, instead of by its proper 

 definition as a certain quantity of gold. 



II. So long as the gravitation unit of force alone was 

 employed, the same number, which expressed the number 

 of the weights which equilibrate the body, also expressed 

 the number of pounds of force with which the Earth ap- 

 peared to attract the body ; and it is only in this sense 

 that the weight of a body is " the force with which it is 

 attracted by the Earth " ; it is essential that the unit of 

 force should be the gravitation unit, when this definition 

 is employed. 



We say, for instance, in Hydrostatics, that a ship is 

 buoyed up by the water with a force equal to the weight 

 of the displaced water, which is also equal to the weight 

 of the ship, when in equilibrium. 



Again, the head of water which will produce a pressure 

 of 150 lbs. on the sq. inch, is always 



150 X 144 -r- 625 = 3456 feet, 



whatever the local value of g ; the numerical measure is 

 always the same, although the amount may differ in con- 

 sequence of the variation of g and the unit of force. 

 A boiler tested to 150 lbs. on the square inch is tried 

 one -2 5th per cent, more severely in Glasgow than in 

 London. This variation, at most \ per cent., is not 

 likely to lead to litigation — De minimis non curat lex. 



There is no particular harm in the use of the word 

 mass, provided it is always measured in the standard 

 units of weight ; there is this drawback, that there is no 

 verb to "mass " ; we can say that the body weighs W lbs., 

 but we cannot say it "masses" M lbs. 



Again, the Acts of Parliament do not regulate " Masses 

 and Measures," but " Weights and Measures," " Poids et 

 Mesures," " Maasse und Gewichte," " De Ponderibus et 

 Mensuris." 



The French language possesses the two words Poids 

 and Pesanteur, both of which we translate by Weight. 



Poids may be translated mass, or quantity of matter, 

 copia viatericE ; but that does not justify the degradation 

 of weight down to the meaning of pesanteur, and that 

 merely ihe pesanteur on the surface of the Earth ; having 

 already invented mass, the theorist must invent a new 

 word to translate pesanteur; the word heft has been 

 suggested, but the word weight must be left alone, to do 

 double duty occasionally. j 



A libellous story of the Hudson Bay Company says j 

 that in their former dealings with the Red Indians, the 1 

 weight of the factor's fist was always one pound ; a good j 

 illustration of weight as meaning both poids andpesanteur 

 to ignorant minds. 



An amusing instance of the confusion of using weight 

 in the double sense oi poids and pesattteur, when not 

 restricted to the provincial gravitation unit of the surface 

 of the Earth, on which the human race is imprisoned, 

 occurred in a lecture last year on Popular Astronomy. 

 To illustrate the fact that g on the surface of the Sun is 

 about 30 times greater than it is here (§ 5), the lecturer said, 



NO. I 185, VOL. 46] 



" An ordinary middle-aged man of this audience, if trans- 

 ported to the surface of the Sun, would weigh about two 

 tons ; but his reflections on this difficulty would be cut 

 short by the immediate prospect of being converted inta 

 two tons of fuel.'" 



12. Maxwell unfortunately lent his powerful aid to the 

 attempt to degrade the word weight to mean merely 

 pesanteur. 



In a review of Whewell's " Writings and Correspond- 

 ence," edited by Todhunter, Maxwell writes that — 



" Finding the word weight employed in ordinary lan- 

 guage to denote the quantity of matter in a body, though 

 in scientific language it denotes the tendency of that body 

 to move downwards, and at the same time supposing that 

 the word mass in its scientific sense was not sufficiently 

 established to be used without danger in ordinary lan- 

 guage. Dr. Whewell endeavoured to make the word 

 weight carry the meaning of the word mass. Thus he 

 tells us that — the weight of the whole compound must 

 be equal to the weight of the separate elements." 



" It is evident that what Dr. Whewell should have said 

 was — the mass of the whole compound must be equal to 

 the sum of the masses of the separate elements." 



But Whewell was quite right, because, at the time he 

 wrote, mass was merely the printer's abbreviation for 



W 



" We are reminded by Mr. Todhunter that the method 

 of comparing quantities by weighing them is not strictly 

 correct." (Compare this statement of Todhunter with 

 that of Dr. Harkness in his article on " The Art of 

 Weighing and Measuring," Nature, August 15, 1889, p. 

 381, where it is pointed out that weighings can be carried 

 out to within one lo-millionth part.) 



Again, in Maxwell's " Theory of Heat" (p. 85), we read 

 " In a rude age, before the invention of means for over- 

 coming friction, the weight of bodies formed the chief 

 obstacle to setting them in motion. It was only after 

 some progress had been made in the art of throwing 

 missiles, and in the use of wheel-carriages and floating 

 vessels, that men's minds became practically impressed 

 with the idea of mass as distinguished from weight. 

 Accordingly, while almost all th^ metaphysicians who 

 discussed the qualities of matter, assigned a prominent 

 place to weight among the primary qualities, few or none 

 of them perceived that the sole unalterable property of 

 matter is its ?nass." 



The question in dispute resolves itself, then, merely 

 into a difference of terminology ; and the metaphysicians 

 are using the language universally employed up to the 

 middle of this century, and are justified on all sides in 

 their usuage : Maxwell might as well have criticized the 

 traditional names which astronomers employ for the 

 heavenly bodies. 



Maxwell would even have edited the authorized and 

 revised version of the New Testament ; in tocrtX Xlrpas 

 «Kardf— translated "about an hundred pound weight" — 

 (John xix. 39), he proposed the omission of weight, 

 probably inserted in the version to make a distinction 

 from pounds sterling. 



This addition of the word weight is common elsewhere, 

 thus, " His Majesty's Warrant, August 19, 1683, to cause 

 3 barrels of fine pistol powder, 3 cwt. weight of pistol 

 bullets, and 3 cwt. weight of match to be delivered to 

 John Leake, Master Gunner, for the use of the 3 troops 

 of Granadiers, &c." ("Notes on the Early History of the 

 Royal Regiment of Artillery," by Colonel Cleaveland). 



Dr. Lodge says that the term hundredweight bears 

 marks of confusion on its surface, and had better be 

 avoided ; what does he say to this use of hundredweight 

 weights, not intended to mean pull of gravity ? 



This Warrant is dated four years before the first edition 

 of the " Principia," in which the downward tendency of a 



