522 Prof. Maxwell and Mr. F. Jenkin on the Elementary 



tions is very wide. We have to measure the intrinsic energy of 

 substances as dependent on volume, temperature, and state of 

 combination. When this is done, the energy due to any combi- 

 nation will be found by subtracting the energy of the compound 

 from that of the components before combination. 



As the tendency to increase in volume is measured as pressure, 

 and as the tendency to part with heat is measured by the tempe- 

 rature, so in chemical dynamics the tendency to combine will be 

 properly measured by the electromotive force of combination. 



55. Tables of Dimensions and other Constants: — 



Fundamental Units. 

 Length = L. Time = T. Mass = M. 



Derived Mechanical Units. 

 Work=W=™. Force =F=™. Velocity = V= ^ 



Derived Magnetical Units. 

 Strength of the pole of a magnet . m=L^ T _1 M^ 



Moment of a magnet ml—1^ T _1 M* 



Intensity of magnetic field . . . H = L"^T _1 M* 



Electromagnetic System of Units. 



Quantity of electricity Q=Li x M^ 



Strength of electric current . . . C = L^T~ 1 M£ 



Electromotive force E = I#T~ 2 M* 



Resistance of conductor R=L T" 1 



Electrostatic System of Units. 



Quantity of electricity <7 = I^ T _1 M^ 



Strength of electric currents . . . c=L£ T~ 2 M^ 



Electromotive force e=Li T _1 M^ 



Resistance of conductor r=L _1 T 



Let v be the ratio of the electrostatic to the electromagnetic 

 unit of quantity (35 and 46) ; then v — 310,740,000 metres per 

 second approximately, and we have 



q = vQ 



c—vQ 



e=-V 

 v 





s=v*S 



