424] 
ON THE ATTRACTION OF A TERMINATED STRAIGHT LINE. 
33 
Joachimsthal, “ On the Attraction of a Straight Line,” with Sir W. Thomson’s Note, 
Camb. and Dubl. Math. Journ., vol. ill. (1848), p. 93; but it does not appear to have 
been noticed that they are, in fact, included in the theory of the attraction of 
ellipsoids. 
The like considerations show that the attractions of the ellipsoidal shell (a, b, c; e) 
• • ocF vF 
upon an exterior point are equal to those of an elliptic disk z = 0, — -+ -f-—-=1, 
r r ™ ^ ^ a 2 — c 2 o 2 — c 2 ~ ’ 
the mass of which is equal to that of the shell, and which has the density at the 
point (x, y) proportional to ( 1 — 
Sir W. Thomson informs me that the foregoing results have long been familiar to 
him.