We now have 



km 



h* (a® + l) s ' 2 



(10) 



Jem . 



Here the dimensions are contained in the factor and for a particular 



A 2 



value of h would have to be computed only once. The factor — - 7TJJI — 



is dimensionless and would need be computed but once to hold for all values of h. 

 We may think of a as a measured in units of h. 



ATTRACTION OF Expressions for the attraction of distributions 



EXTENDED BODIES of mass which may not be regarded as parti- 



cles may be formulated by dividing the body 

 into small elements and summing their separate attractions according to the 

 procedure used in the calculus. Thus, the attraction dA of an element of mass 

 dm situated at the source point Q{u,v,w) is given at the field point P(x,y,z) by 



dA = - _*!*2_ (ll) 



dA = ^ dudvdw (12) 



where the mass element dm has been replaced by the product of the density p 

 and the volume dudvdw of the element. The attraction of the entire body is 

 then given by 



A = -k C C C-P±- dudvdw (13) 



and the components A x , A y , A z by 



A m = -kfff P(X 7 7 U) dudvdw (14) 



A y = -kfff p(y ~ V) dudvdw (15) 



A z = -kf f f P(Z ~ W) dudvdw (16) 



588 



