Chase.] 4:bJi [June 17, 



cept Mq and G„, or Sun's mass and superficial gravitation, as standards of 

 comparison between Sun's centripetal and centrifugal, or gravitating and 

 radiating energies. The Sun itself is subject to the paramount control of 

 uniA^ersal mass and gravitation. Although we have no means of finding 

 their absolute or relative value, we may symbolize them by M^ and Gy and 

 thus seek for standard values of L^ and T,,. Every particle of the Sun is 

 conflnually solicited by G^ and G^, and their varying solicitations can be 

 compensated only by cj^clical alternations of rise and fall, from and to- 

 wards the universal centre of gravitation, c„. In order that Sun's mass may 

 be stable, the sum of the tendencies of G^ must be equal to the sum of the 

 tendencies of Gry, during each half-rotation. A solar half-rotation, therefore, 

 may be taken as a natural standard value for T^ ; then the equation M^ H^ = 

 2M„ /H„\2 G„T„2 



~C~ ^ vT" / o^^^^ -^0 = — 9 — ' ^^^ Lq = 2 Ho=: Go To^ as a correspond- 

 ing natural standard of length and distance. 



72. Standard Kinetic Modulus. 



If we examine the equation which we have found in the foregoing note 



for the natural unit of length, we find that H^ represents the height of 



virtual fall which would give a velocity equivalent to G^ T^, and L^ is the 



height of a homogeneous elastic atmosphere which would have a velocity of 



L„ 

 wave-propagation equivalent to rfr = G^ T^ = G„ T^,, the actions and re- 



actions of G^, and G„ being equal. But the elastic atmosphere, in which 

 these actions and reactions take place, is the universal gethereal medium, 



and its velocity of wave-propagation, prr, is the velocity of light. The re- 

 lations of heat, mass and gravitation, therefore, lead us to the same funda- 

 mental velocity as the relations of the electrostatic and electromagnetic 

 systems, and the same velocity as the solar radiations which are variously 

 modified so as to produce the phenomena of light, heat, electricity, mag- 

 netism and actinism. Our knowledge of the significance of the electrical 



unit IS thus extended, so as not only to include the ratio ^r, but also to 



show that the natural standard units of mass, length, and time are, re- 

 spectively. Mo = Sun's mass ; L^ := standard kinetic modulus, or Solar 

 modulus of light ; T^ = half-time of solar rotation, or time of cyclical 

 equality of action and reaction between solar inertia and aethereal undula- 

 tion. 



73. Variable Units. 



In comparing arbitrary and variable units with the maximum standards, 

 we have generally to deal with fractional values. In uniform velocities, 

 like those of light, electricity, and primitive kinetic radiation, I oa t; \n. 

 variable velocities which are due to centriiDctal or centrifugal radiation, 

 like those of gravitation and heat,, I oc t^. Maxwell* gives electric di- 



*0p. cit., ii, ? 620-9. 



