396 Prof. R. Clausius on the different Systems of 



mental unit, the first three lower units resulting from divisions 

 by ten are named by prefixing the words deci, centi, and milli, 

 borrowed from the Latin, and the first four higher units, 

 resulting from multiplications by ten, by prefixing the words 

 deka, hekto, kilo, and myria, borrowed from the Greek. I 

 propose, then, to employ for naming the lower units arising 

 from further divisions by 10, and the higher units arising 

 from multiplications by ten, likewise Latin and Greek nume- 

 rals, but ordinal numerals, which will specify the negative or 

 positive exponents of the powers of ten by which the funda- 

 mental unit is to be multiplied; so that, for instance, with the 

 metre the fifth lower unit l.l0 _5 m will be called a qninto- 

 metre, and the fifth higher unit 1 . 10 5 m a, pemptometre , and cor- 

 respondency with the gram and other fundamental units*. 



According to this, we have to call the mass 1 . 10 -11 ^?*, 

 occurring in the above system, an undecimogram, and the 

 length 1 . 10'm a hebdometre. The practical system of mea- 

 sures is consequently characterized in its entirety by the 

 name the electrodynamic system of measures undecimogram, 

 hebdometre, second. This name easily impresses itself in the 

 memory; and by it the aim of a more precise definition of the 

 system is more perfectly attained than by saying that it is the 

 electrodynamic system of measures gram, centimetre, second, in 

 which, however, each unit must be multipied by a specially to 

 be stated power of ten. 



§ 9. The Critical System. 

 We have seen, in section 5, that, in the different kinds of 

 electric and magnetic quantity, the ratio of the dynamic unit 

 to the value of the static unit measured according to dynamic 

 measure, or, what comes to the same, the ratio of the value of 

 the dynamic unit measured according to static measure to the 

 static unit, is always represented by a power of the ratio of 

 the critical velocity to the velocity-unit. It thence follows 

 that, if the fundamental units be chosen so that the velocity- 

 unit becomes equal to the critical velocity, then those ratios 

 become each equal to 1. A system of measures in Avhich this 



* Only the higher unit resulting from multiplication by 10 6 makes a 

 little difficulty. As the sixth is euros in Greek, in accordance -with the 

 above we should have, properly, to call the quantity 1 . 10*»i a hecto- 

 metre. But in the French system of measures the prefix hekto is already 

 employed in another sense, namely as a contraction of eKarov, so that heh- 

 tometre signifies lOOw ; and. Ave must therefore seek help from some other 

 source for the naming of 1 . 10 6 . To that end we might, e. g., deviating 

 somewhat from Greek usage, say hexometre, or even employ the prefix 

 mega, proposed for this order of quantity by the British Association, and 

 form the name megametre, 



