VOL. LXVI,] FHILOSOPHICAL TRANSACTIONS. n 



from die centre, and the axis perpendicular, the whole will be balanced on the point at b, and move- 

 able on it by an impelhng power, witli very little friction. On the upper part of the axis are formed 

 2 cylindrical barrels, m, n, of which m is double tlie diameter of n ; and they have a little pin 

 stuck into one side of each at o, p. 



Q is a piece capable of sliding higher or lower, as occasion requires ; and carries r, a light pulley 

 of about 3 inches diameter, hung on a steel axis, and moveable on 2 small pivots. The plane of the 

 pulley however is not directed to the middle of tlie upright axis, but a little on one side, so as to 

 point (at a mean) between the surface of the larger barrel and the less, s is a light scale for receiving 

 weights, and hangs by a small twine, cord, or line, that passes the pulley, and terminates either on 

 the larger barrel or the less, as may be required ; the sliding-piece q being moved higher or lower for 

 each, tliat the line, in passing from tlie pulley to the barrel may be nearly horizontal. The end of 

 the line farthest from tire scale is terminated by a small loop, whicli hangs on the pin o, or the 

 pin p, according as the larger or the lesser barrel is to be used. 



Now, having wound up a certain number of turns of die line on the barrel, and having placed a 

 weight in the scale s, it is obvious, that it will cause the axis to turn round, and give motion to its 

 arms, and to the weights of lead placed on diem, which are the heavy bodies to be put in motion by 

 the impulse of the weight in the scale ; and when the line is wound oft" to the pin, the loop slips off, 

 and the scale then falling down, die weight will cease to accelerate the motion of die heavy bodies, 

 and leave them revolving, equably forward, widi the velocity they have acquired, except so far as it 

 must be gradually lessened by the friction of the machine and resistance of the air, which being 

 small, die bodies will revolve some time before their velocity is apparently diminished. 



Measures of some Paris oj the Maeliiiie. 



Inches. 



Diameter of the cylinders of lead, or the liea\7 bodies 2.57 



Lengdi of ditto l.^'S 



Diameter of the hole in them 72 



Weight of each cylinder 3lbs. Avoirdupois. 



Greater distance of the middle of each body from the centre of die axis 8.25 



The smaller distance of ditto 3.^2 



\ turns of die smaOer barrel, or 5 of die larger raises die scale 25.2 j 



When the bodies are at the smaller distance from the axis of rotation, they 

 are then in effect at half the greater distance from that axis ; for, since the axis 

 itself, and the c) lindric arms of wood, keep an unvaried distance from the centre 

 of rotation, the bodies themselves must be moved nearer than half their former 

 distance, in order that, compounded with the unvariable parts, they may be vir- 

 tually at the half distance. In order to find this half distance nearly, I put in 

 an arm of the same wood, that only went through the axis, without extending 

 in the opposite direction ; one of the bodies being put on the end of this arm, 

 at the distance of 8.25 inches, the whole machine was inclined till the body and 

 arm became a kind of pendulum, and vibrated at the rate of 92 times per 

 minute ; and as a pendulum of the half length vibrates quicker in the propor- 

 tion of v/1 to /2; that is, in the proportion of 92 to 130 nearly; therefore, 

 keeping the same inclination of the machine, the weight was moved on the arm 

 till it made 130 vibrations per minute ; which was found to be, when it was at 

 3.92 inches distance from the centre as above stated, which is about VVths of an 

 inch nearer than the half distance. The double arm was then put in, and 

 marked accordingly, and the bodies being mounted on it, the whole was adjusted 



