upon the Collijton of Bodies. 347 
Tlicfc ideas arofe from the' relult of the experiments tried 
upon the machine deferibed in my faid trad upon Mechanic 
Power, and were alfo communicated to my very worthy and 
ingenious friend william kussell, Efq. F. R. S. at the fame 
time that I ihewed him thofe experiments in 1759 ’ but the 
mode of putting this matter to a full and lair mechanical trial 
has lince occurred ; and though fome rough trials, fufficient to 
fhew the effed, were made thereon, prior to the offering the 
paper on mechanical power to the Society in 1 776, yet the 
machine itfelf I had not leifure to complete to my fatisfadion 
till lately ; which I mention to apologize for the length of 
time that thefe fpeculations have taken in bringing forward. 
PESCRIPTION OF THE MACHINE FOR COLLISION. 
Fig. i. fhews the front of the machine as it appears at reft 
when fitted for ufe. 
A is the pedeftal, and AB the pillar, which fupports the 
whole, C, D are two compound bodies of about a pound weight 
each, but as nearly equal in weight as may be. Thefe bodies 
are alike in conftrudion, which will be more particularly ex- 
plained by fig. 2. Thefe bodies are fufpended by two white 
fir rods of about half an inch diameter ef and gh, being about 
four feet long from the point ol fufpenfion to the center of the 
bodies ; and their fufpenfion is upon the crols-piece II, which is 
mortoifed through, to let the rods pals with perfed freedom ; 
and they hang upon two imall plates filed to an edge on the 
under fide, and pafs through the upper part of the rods. Their 
centers are at k and /, and the edges being let into a little 
notch, on each fide the mortoife, the rods are at liberty to 
vibrate freely upon their refpedive points (or rather edges) of 
fufpenfion, and are determined to one plain of vibration. MN 
flat arch of white wood, which may be covered with 
Z z 2 
is a 
