304 On the Parallelogram of Forces. 



and a den for thieves,) you, with other gentlemen and myself, were 

 by tire 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 

 Phoenix 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 steam engine is withdrawn, it will be found, that the principal vessel, 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 j but if provided, it is plain in what man- 

 ner these vessels may be guarded from lightning. 



March, 1834. 



Akt. V. — On the Parallelogram of Forces ; 



by Prof. Theodore Strong. 



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 

 that in 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 xX 1 ; 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 



