168 
Which one possessed, nor pause nor quiet knew 
The sure associate, ere with trembling speed 
He found its path and fixed unerring there. 
^Pleasures of the Imagination, Book iii.) 
This passage is cited in Dr. Thomas Brown’s Philosophy 
of the Human Mind, (16th ed., 1846, ii. 220). 
Strada’s fancy is also referred to in the Abridgements of 
Specifications relating to Electricity and Magnetism (1859, 
p. xliii), “Saturday Keview,” August 21, 1858, p. 190; 
Moigno : Traite de Telegraphie Electrique, p. 58-59, and in 
Keddie’s Literary and Scientific Anecdotes, where several 
of the above references are to be found. 
It is to be noticed that the effect is ascribed to the power 
of sympathy. This was an important doctrine of the time, 
and reached transcendental heights in the hands of Sir 
Kenelm Digby. 
“On the Law of Force when a Thin Homogeneous • 
Spherical Shell exerts no Attraction on a Particle within 
it,” by J. H. PoYNTiNG, B.A., B.Sc. 
If a homogeneous thin spherical shell of uniform thick- 
ness exert no attraction on a particle within it, then the 
law of the force is the law of nature. 
Professor Maxwell uses this proposition (Electricity, 
vol. i., § 74) to deduce the law of the force between 
electrified bodies, and shows that it proves far more con- 
clusively than any direct measurements of electrical forces 
that the law is that of the inverse square. It would there- 
fore be an advantage to have a simpler proof of such an 
important proposition than that given by Laplace (Mec. 
Celeste, liv. ii., cap. 2) and followed by Maxwell. The 
following seems more simple as it requires neither integra- 
tion nor the solution of a functional equation : — 
Let P be any point inside the spherical shell, C the centre 
of the sphere, DPCE the diameter through P, and APB 
