244 Mr KELLAND, ON THE MOTION OF 



R its distance from that point: then it is manifest that the only dif- 

 ference in the form of this term will be, that in the present case the 

 difference of the co-ordinates of the two particles parallel to the axis 

 of X, instead of being A.r + « + ^a-a, is A:r-a; whence we obtain, 

 supposing the force to vary inversely as the square of the distance, 



but {R + l\Rf = (Aa; - af + Ay' + As' 



R' -I- 2RAR = R' - 2 Ax. a; 



„ Ax 



.-. AR = "^' 



whence by substitution we get 



d'a ^„ (Ax - a\ ( Ax\ 



= - Q2 (ax - a + 3a-^) -^3 -h &C. 

 = QS^(i2' - 3Ax-).a + &c. 



= Q2^(A/ + Aa' - 2Aa;=) + &c. 



Ay- ^Ais' ^ Ax- 

 Now 2-^=2^ = 2^, 



hence the expression 2-pT(Ay' + Ax' - 2 Ax') is zero, 



and the velocity is independent of Q; the only effect which is pro- 

 duced by the material particles being an indirect one, arising from the 

 alteration of distance which they produce in the particles themselves. 



