486 



NA TURE 



\J\Iarch 24, 1887 



Royal Society, if Ihose islands were confederated for meteoro- 

 logical purposes.^ 



The writer was apparently unaware that in the year 1879 

 those islands agreed to confederation. It was not restricted 

 to the British colonies — Guadaloupe, for instance, passed a 

 vote of credit through its chamber before the decision of the 

 British Meteorological Council was received — but all the work 

 broke down when the Meteorological Council insisted upon 

 Antigua as the central station. 



It is unnecessary to say that unmitigated failure was the 

 result. 



The advantages to the United .States of any West Indian 

 system, however poor, are palpable to the lowest stratum of 

 scientific intelligence ; yet we find that Congress disestablished 

 the whole of their West Indian stations without the slightest 

 reason, as far as I have been able to discover. But the words of 

 the Chief Signal Officer have a thousand times the weight of 

 mine, and I quote them accordingly : — 



"Among the objects fur which appropriations were refused were 

 'foreign reports.' A request was made for 4000 dollars to pay 

 for these warnings of tropical hurricanes, which, last year, were 

 instrumental in saving millions of dollars of property. Two 

 storms of great fury swept up from the Gulf, one in September 

 and one in October. Warnings of the coming of these storms 

 w ere given from the West India stations, so that the indications 

 officer on duty in each month was able to give at least two days' 

 notice of the coming of the storm to every port in the Gulf and 

 on the Atlantic coast. The result was an immense saving of 

 valuable property and of human life. The statistics were 

 gathered as fully as possible from all the stations passed over by 

 the cyclones, and the names of the vessels, their value, and the 

 value of their cargoes, remaining in port in obedience to the 

 storm warnings of this service, were ascertained. The reports 

 were not wholly satisfactory, because accurate information 

 could not be obtained from the largest places of the country, 

 such as New York, Philadelphia, Baltimore, and Boston. 

 These cities lie at the head of large harbours that have safe 

 anchorages near their openings, and vessels delayed by a storm 

 almost invariably go down the harbour to there await its conclu- 

 sion. But, without these great ports, it was ascertained that 

 6,460,586 dollars of properly remained safe in harbour during the 

 September cyclone, and 6,051,393 dollars in October. The 

 failure to appropriate tlie 4000 dollars asked for for the current 

 fiscal year has reduced the warnings received from the West 

 Indies, and made it less possible to predict with certainty the 

 approach of tropical hurricanes." (Report for 1883, p, 4.) 



The anticipations of the Chief Signal Officer have been fully 

 confirmed. 



In the face of such opposition I would ask what is the use of 

 proposing schemes of confederation requiring the support of the 

 authorities ? There is no doubt that if meteorological confedera- 

 tion is to obtain in the West Indies, it must be done among the 

 British colonies themselves ; but who will come forward to 

 undertake such a task ? Should anyone attempt it, he will 

 at least have the supjiort of Jamaica. 



Maxwell Hall, 



February 15 Jamaica Government Meteorologist 



Units of Weight, Mass, and Force 

 Your reviewer, of the well-known initials "P. G. T.," has 

 taken exception to some of the terminology employed by Mr. 

 Anderson in his book " On the Conversion of Heat into Work," 

 particularly to the expressions of "pounds on the square inch" 

 and " tons on the square inch," which he says would define a 

 superficial density if used in their proper sense ; and it is this 

 opinion I wish, with your permission, to dispute, as I think 

 " P. G. T.'' and mathematicians generally, are at present in this 



endeavour to avoid one ambiguity in dynamical language only 

 creating greater confusion. 



I presume that " P. G. T." would have been satisfied with the 

 above expressions provided the word " weight " had been intro- 

 duced somewhere ; but let us examine carefully what is implied 

 by " weight " as used in ordinary language. 



Turning to the chapter on elementary dynamical principles in 

 Maxwell's "Theory of Heat, "we find that "the viaxAweight rcmsX 

 be understood to mean the ijuaiility of the thing as determined by 

 the process of weighing against standard iveights^ And again : — 

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

 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 im- 

 pressed with the idea of mass as distinguished from weight." 



The language we employ, including the use of the a'libiguous 

 word "weight," was formed in this rude age before the discovery 

 of true dynamical principles and before the theory of gravitation, 

 and now, in order to avoid ambiguity, the mathematician uses, 

 wherever it is possible, the word "mass" for greater precision, 

 where an ordinary person would use the word weight. 



But unfortunately for his principle the rules of language do 

 not permit him to be consistent, and he is compelled to speak of 

 "weights and measures" and of "bodies weighing so many 

 pounds or tons" instead of "bodies massing so many pounds," 

 or ' ' masses and me isures, " which might be mistaken for a 

 political phrase. 



The word ' ' weight " will, then, be found to be used in ordinary 

 language in most cases in the same sense as the word "mass," 

 introduced with laudable intention by the mathematicians to 

 avoid confusion ; but unfortunately some mathematicians intro- 

 duce greater confusion than they remove by appropriating the 

 word "weight" to the subsidiary sense of the word, undistin- 

 guishable by those ignorant of dynamics, namely, the force with 

 which the earth attracts the weight. 



Thus we find in ordinary treatises on dynamics, after an effort 

 at the definition of the mass, the weight of a body defined ai 

 "the force with which it is attracted by the earth." 



As Maxwell says, "The only occasions in common life in 

 which it is required to estimate weight considered as a force is 

 when we have to determine the strength required to lift or carry 

 tilings, or when we have to make a structure strong enough to 

 support their weight." Herein is comprised in general terms the 

 whole province of the theory of engineering, and consequently 

 the engineer always employs the gravitational measure of forces. 

 The force with which the earth attracts the standard weight is 

 taken as the gravitation unit of force ; and for brevity the force 

 with which the earth attracts a pound weight (the mathematician 

 would say a pound mass) is called the force of a pound, abbre- 

 viated again to "a pound." Hence we have steam pressures, 

 gunpowder pressures, moduli of elasticity, tenacities, &c., as well 

 as the expressions objected to by " P. G. T." in Mr. Anderson's 

 book, expressed in pounds or tons on the square inch, without 

 creating any confusion in the mind of the practical man ; and we 

 find the words "pound" or "ton "used side by side, now in 

 the sense of weight or mass, and now in the sense of force ; as, 

 for instance, in the statement, " A train, weighing 100 tons 

 moving against a resistance of 20 pounds a ton, is drawn by an 

 engine exerting a pull of 2 tons, Sec." 



But when the practical man opens the ordinary text-book on 

 dynamics, then the confusion begins. Take, for instance, the 

 familiar equation l-V=Mg: what does it mean? The writers 

 tell us that 11^ means the weight and JIf the mass of the 

 body. Having defined "weight "as the force with which the 

 body is attracted by the earth, the writer implies that be is 

 keeping to the statical gravitational unit of force, and therefore 

 his unit of mass is the mass of g pounds, if IF, the weight, is 

 measured in pounds. But, after defining a pound as a unit of 

 mass, he ought to take yi/as the weight in pounds, and then the 

 equation IF = A/g means that the earth attracts Af pounds with 

 a force of IV poundals where IF— A/g. 



The confusion is intolerable ("most tolerable, and not to be 

 endured"), andentirely dueto the erroneous mathematical defini- 

 tion of the word "weight," combined with straining the units of 

 mass and force so as to fit into the equation /" = yl^ when 

 absolute units are not employed. 



To show the absurdity of the definition that "the weight of 

 a body is the force with which it is attracted by the earth," 

 take the question, " What is the weight of the earth ? " Accord- 



