MECHANICS. 79 



136. When one wheel moves another in either 

 of these ways, the velocities of their circumfer- 

 ences are equal ; and therefore their angular velo- 

 cities, or the number of revolutions which they 

 make in the same time, are inversely as their ra- 

 dii. 



In combinations of wheels communicating motion to 

 one another, it is usual to call a smaller wheel 

 acted on by a larger one, a pinion ; and its teeth 

 the leaves of the pinion. Sometimes the smaller 

 wheel is a cylinder, in which the top and bottom are 

 formed by circular plates or boards, connected by 

 staves inserted at equal distances along their cir- 

 cumferences, serving as teeth ; this is called a lan- 

 tern. It is usual also to employ wheels and pi- 

 nions, as in figure 9, where A is a large wheel, 

 driving a pinion b on the same axle with the great 

 wheel B ; B acts on the pinion c, which is on the 

 same axle with the large wheel C ; and C drives the 

 pinion J, &c. 



137. When motion is communicated through a 

 number of wheels and pinions, the angular veloci- 

 ty of the first wheel, is to the angular velocity of 

 the last pinion, as the product made by multiply- 

 ing together the number of the teeth in every pi- 

 nion, to the product made by multiplying together 

 the number of the teeth in every wheel ; and that 

 same ratio, compounded with the ratio of the ra- 

 dius of the last pinion, to the radius of the first 



wheel, 



