304 On the Parallelogram of Forces. 
and a den for thieves,) you, with other gentlemen and myself, were 
by the late king Charles, named commissioners to survey the dilapi- 
dations ; and to make report to his Majesty, in order to a speedy re- 
formation. You will not, I am sure, forget the struggle we had with 
some, who were for patching it up any how, (so the steeple might 
stand,) instead of new building which it altogether needed ;—when, to 
put an end to the contest, five days after, that dreadful conflagration 
happened [namely, the great fire of London,] out of whose ashes this 
Phenix is risen. The circumstance is so remarkable, that I could 
not pass it over without notice.” 
_ N. B.—On revising the above Supplement, a seeming neglect 
will be observed. It is said, that steam boats have not been liable to 
suffer by lightning, which is correct; and is owing to the influence of 
the edges and points of the iron tubes of steam boats, and to the va- 
por thrown forth by them, &c. and perhaps to masts. But, when the 
steam engine is withdrawn, it will be found, that the principal vessel, 
and the little vessel in the wake of this principal vessel, will then be 
left unprotected as to lightning. Masts and rigging for these two ves- 
sels, were not hinted at, although they might have been; nor will 
they now be insisted upon; but if provided, it is plain in what man- 
ner these vessels may be guarded from lightning. 
March, 1834. 
Art. V.—On the Parallelogram of Forces ; 
by Prof. THEopore Srrone. 
WHATEVER moves a body, or tends to move it, or alters its mo- 
tion in any manner, is called force. The direction of the force, is 
thatin which it tends to affect the motion of the body. Two forces 
are equal, when being applied to a material point in opposite direc- 
tions, they destroy each other’s effects. If any number of equal 
forces, each represented by unity, are applied at once to a material 
point in the same direction; then if x denotes their number, the point 
is said to be acted on in that direction by the force x X15 or simply, 
by the force x. When any number of forces acting in any direc- 
tions, are simultaneously applied to a material point, if they do not 
balance each other, the point will evidently move, or tend to move, 
in a certain direction, (by their action,) in the same manner that it 
