526 



SCIENCE 



[N. S. Vol. LII. No. 1353 



suits lately obtained on the atomic weights of the hence the adoption of such a unit would 



isotopes of lead and of neon indicate that one obviate the necessity of having one unit for 



sixteenth of the atomic weight of oxygen is very theoretical and another for practical work, 



near indeed to the unit mass of the Prout hy- -rr n i • 1 1 i . ,. . , 



ii, ■ T, i -i • -u- -ui • -u 1.1 4.-U i -J. -u ij -tmally, by a suita;ble selection of a unit of 

 pothesis, but it is highly improbable that it should 



be identical with it. (It would require that oxygen ™^f^ *^^ electromagnetic and electrochemical 



consist of one isotype only— or a still less prob- ^^^^^ °^^ ^^ brought into harmony. (It 



able balancing of heavy and light isotopes.) should be noted that this involves giving up 



„, „ ,. • ,. 11 the use of water as a standard ,of density.) To 



Ihe most flagrant case oi irrationally re- . .^ . ■„ t , , . i 



, ^ J ^ . ., • ,1 , J. 1 ^ • 1 summarize: it is possible — ^by making the nu- 



lated metric units is that oi electrical quan- . , , , ^, , ., ,.,.,/ 



^., J, 1 . 1 J. ., , r I,- 1, merical value of the velocity of light a power 



tity, tor which four units, no two ot wnich are j: -in i -^ ii ^ ■ ^^ ■, r 



.. . . „, o± 10, by suitably choosing the unit of mass, 



commensurable, are m actual use. ihese ,, . _,, -rr •■-,■, r. ■ ■ 



. /-N ,1 1,1 -1 ■ T ^ <■ and by using the Heaviside definition of unit 



four are (1) the electrochemical equivalent of, ^j- -i -^ ^ ■, ■ ■, 



, ^ . ., T^ 1 /ns.i 1 t, T.-1. charge — to derive a single unit of electrical 



electricity, or Faraday, (2) the coulomb, which ... .^ , , . ,, 



' . , . , , quantity suitable for all purposes. 



IS one tenth of the centimeter-gram-second -rr j. j , , -, , i i 



, . -, /ON J ^- J. Meat and temperature units are to be de- 



electromagnetic unit, (3) the centimeter-gram- • j i i i ■ j ^ •,- -.i . 



, , , , ,. .; J /,s ^1 UTT • rived by purely dynamic definitions, without 



second electrostatic unit and (4) tne Heavi- i , ,i ,• ^ ,i , 



.J „ , , ... ■. j-a ■ 4? j-i, regard to the properties of the substance, 

 side electrostatic unit, dittering ±rom the tt • • i 

 foregoing by the factor 1/V4"-, and used by ^f.^'' ^^'^ temperature is the temperature at 

 Lorentz and others in electron theory calcula- ^^''^ ""^^^ concentration of a perfect gas" 

 tions in order to give a simple form to tbe ^^'^^ "°'* P''^^^^^^ °'' ^^^ ^^^^^ °f it^ e°^- 

 fundamental equations for the electromagnetic ^^'''^^' ^^'^^ *e difference between the heat 

 field. The ratio of the electromagnetic to the capacities of a mol of "perfect gas " at con- 

 electrostatic unit is numerically the same stant pressure and at constant volume is the 

 as the velocity of light, hence a reconcilia- unit of heat capacity and ,of entropy, 

 tion is possible only in a system which In Table I. are given the numerical factors 

 makes the numerical velocity of light a which, in various combinations, are involved 

 power of 10. A unit of the Heaviside in conversion between the proposed units and 

 type is quite satisfactory for practical use, those of the centimeter-gram-second system. 



TABLE I 



Symbol Daflaltlon Numerical Value^ 



4ir Ratio of area of sphere to square of radius 12,5664 



10° Numerical value assigned in proposed system to the veloc- 

 ity of light and to the electrochemical equivalent^ .... 12.5664 



Velocity of light in c.g.s. units 29,986,000,000. cm. per see. 



E Electrochemical equivalent^ in c.g.s. units 9,647.2 units per equivalent 



E Gas constant in c.g.s. units 83,150,000. ergs per mol per °C. 



J Value of the mean calorie in c.g.s. units 41,850,000. ergs per calorie 



Tables II., III. and TV. give the ratios of ITumerical values are given only when the 



the proposed units to those of the metric sys- metric unit compared has a name in common 



tern — both algebraically in terms of the fac- ^gg_ 



tors terms listed in Table I., and numerically. rpj^^ ^^^^^ ^^^ multiples and submultiples of 



2 The values for the last four are taken from the fundamental units would be formed with 

 Kaye and Laby's tables. ^^^ prefixes now in use in the metric system, 



3 The quantity of electricity required to deposit ^i i -i -^ j: i ^ • x j ^i 

 ,,,,.„ ■ ■, \_ 7 X ■, -.^ i, e. a., the kilo-unit ot electric current and the 



eleetrolytically one equivalent of metal, it, the 



electricity in c.g.s. electromagnetic units per equiv- mega-units of pressure and of temperature 



alent, is used instead of F, the number of coulombs would probably be used more than the funda- 



per equivalent, to avoid mixing engineering and mental units; but, aside from the preference 



cg.s. units. of one multiple or submultiple to another, the 



