of Mass, Length and Time. 
155 
discharge of electricity through gases is 11 x 10 -24 gm., or - 07 m. 
There are two other elements marked out by characteristic pro- 
perties, iron and radium. The geometric mean of the weights of 
the atoms of these three is 2'6 x 10~ 23 gm. = T8 m. 
7. The velocity of light is 3 x 10 10 cm./sec. = 4 - 2 x 10 5 1 ft, a 
value which certainly is not small, and cannot be made small 
by any change in the units, for we already have had velocities 
such as 5 x 10 4 and 8*7 x 10 5 . We thus have clear evidence of 
the existence of a fourth fundamental quality of the ether. We 
shall denote the value of the velocity of light in the new units 
by v. If there is no fifth fundamental quality all quantities 
should in the new units reduce to multiples of some power of v 
by numbers that are neither large nor small 
The electric charge associated with a gramme-equivalent of an 
element in electrolysis is an important constant of nature. Its 
value is 2'9 x 10 14 electrostatic* units of charge per gramme or 
75 \/(l s /mt 2 ). 
The still more important quantity, the charge on an electron, 
is unfortunately not known with accuracy. Assuming as above 
that the atom of hydrogen weighs IT x 10 _24 gm., we find it to be 
3 - 2 x 10 -10 c.G.s. = 5 '9 f(ml 3 /t 2 ). 
We shall require to know the new fundamental unit of 
temperature. This may be defined in various ways. Since the 
atomic heats of all elements are nearly the same, we may define 
the unit as the rise of temperature produced by adding one unit 
of energy in the form of heat to m gramme-atoms of the element. 
This gives the value 19° C. Another value, 21° C., is got from 
the moderately constant ratio of the absolute critical point of a 
substance to its density relative to hydrogen. The lowest known 
melting point is of the same order of magnitude. Again if we 
define unit temperature as that at which the kinetic energy 
associated with each degree of freedom of the molecule of a gas 
is unity when expressed in the new units, we obtain 1600k The 
highest temperature at which a solid can exist is perhaps about 
3000°. The mean of these is 210° absolute, or — 63° C. In the 
case of quantities that vary with the temperature we should take 
the values that they have at this standard temperature ; it is near 
enough to take their values at 0° C. 
The minimum electromotive force that will cause a spark 
through air is about 320 volts = IT C.G.S. = 810 This 
number is not small, neither is it of the same order of magnitude 
as v. 
The dielectric strength of insulating liquids is about 200 C.G.S. 
* It is immaterial for our purpose whether we use electrostatic or electro- 
magnetic units, as the resulting numbers will differ only in the ratio of some 
powers of v. For the sake of uniformity, electrostatic units are generally used. 
11—2 
