1881.J 4:61 [Chase. 



probably identical, so that light and electricity may be properly regarded 

 as different modifications of a more fundamental energy. Their common 

 velocity is the greatest known velocity of wave -propagation, and we are 

 thus further encouraged to the study of maxima as indications of kinetic 

 unity. The elements I, t, and m are still arbitrarily assumed in electrical 

 treatises, notwithstanding the suggestiveness of the well-known equation 

 of wave-velocity, « = |/2 gh' 



69. Electrostatic and Electromagnetic Dimensions. 



Although arbitrary values have been assigned to m, I and t, in electrical 

 discussion, the same values are generally assumed in electrostatic and elec- 

 tromagnetic comparisons. It has thus been found that the ratio between 

 the two systems is the velocity of light for quantity of electricity, electric 

 current, magnetic potential, electric displacement, surface density, mag- 

 netic force, strength of current at a point, quantity of magnetism, electi'o- 

 kinetic momentum of a circuit, line-integral of electromotive force, mag- 

 netic induction, electromotive force at a point, and vector potential. The 

 ratio is the square of the velocity for electrostatic or electromagnetic capa- 

 city, dielectric or magnetic inductive capacity, conductivity and resist- 

 ance. The product of these two ratios by mass, furnishes indications of 

 momentum and vis mva which will doubtless be useful in many general 

 kinetic comparisons. 



70. Heat and Gravitation. 



The direct opposition of tendencies in heat and gravitation, the former 

 being centrifugal and the latter centripetal, leads to an easier and more di- 

 rect means of comparison between the tAVO energies than has been found 



ml 

 in the case of light and electricity. But the adoption of mli or -5-, as the 



mechanical equivalent of heat, leaves the relation of gravitation out of 

 view, and it is not readily seen until we tind that mh = — X \T )■ 



Even then, the foot-pound and second, or the kilogrammetre and second, 

 are such arbitrary values that there is no indication of any uniform stand- 

 ard like the velocity of light. We see, on further examination, that our 

 knowledge of heat is wholly derived from phenomena at the Earth's sur- 

 face, where terrestrial gravitation is a maximum, and we are thus led to 

 accept Earth's mass as a fitting natural unit of mass in thermodynamic 



questions, especially in all questions which involve the factor — . In order 



to reach kinetic unity, some values should be found for I and t which can 

 be presented under some simple relation to the velocity of light. 



71. Central Energy of tlie System. 



"We are now somewhat prepared to appreciate the reasoning of Herschel 

 and Stephenson, in referring all terrestrial energies to the Sun, and to ac- 



