138 FUNDAMENTAL UNITS OP MEASURE. 



elation Committee ou Units, led by Lord Kelvin, and includiug such 

 men as Clerk Maxwell, Foster, Stoney, Fleeming Jeukiu, Siemens, 

 Bramwell, Adams, Balfour Stewart, and Everett. Evincing a freedom 

 from national prejudices worthy of the distinguished body which they 

 represented, this committee placed the system of Gauss upon a firm 

 and enduring basis by deriving its fundamental units from the only 

 system of weights and measures which, starting from a scientific basis 

 and constructed upon scientific princiides, has ever found favor among 

 a considerable number of people, and which has now become well-nigh 

 universal. 



The tendency of tlie absolute system is towards simplicity through 

 a reduction of the number of fundamental units to a minimum, while 

 at the same time it aftbrds every facility for the multiplication of 

 derived units to meet the demands of convenience in practice. But 

 however complex and luimerous these derived units may be, they all 

 grow out of the same elements, and are therefore easy of comparison 

 and intei'change. 



It is not too much to say, and it is important that it should be said, 

 that the beauty, simplicity, and convenience of this system are not yet 

 fully understood and appreciated by nmny engineers who might be 

 greatly benefited by its use. As a single illustration, reference may be 

 made to the still very general use of the foot-pound as a unit of work 

 and energy. Let no one imagine that the objection to this unit lies in 

 the fact that units of the metric system are not used, for kilogram- 

 meter, which is also very common, is eijually objectionable. The difli- 

 culty rests in the introduction of a variable, and in this instance unnec- 

 essary magnitude, namely, the force of gravitation. If the funda- 

 mental units, foot, pound, and second, be used, we have a unit of work 

 sometnnes called the "foot-poundal," and if the centimeter, gram, sec- 

 ond system be used, we have the well-known " erg." These units are 

 vastly more convenient in practical use than their gravitation relatives, 

 besides being invariable, whenever and wherever the units of length, 

 mass, and time are invariable. 



Modern scientific metrology may be said to rest upon a few simple 

 principles which may be summarized as follows: 



The number of independent fundamental units sliould be minimnm. 

 In general not more than three are required. 



They should be such as admit of a ready and accurate comparison 

 Avith other magnitudes of the same kind. Units of length, mass, and 

 time satisfy this requirement better than any other that can be selected. 



They should be capable of use for such comparisons at places and 

 times widely separated ; hence they ought to be comparatively easy of 

 re-production and transportation and, as far as human ingenuity can 

 secure, invariable in their magnitude. Units of length, mass, and lime 

 satisfy these conditions better than any other. 



They should also be so related to each other, as far as such relation 



