Ji8 SECTION PHYSICS. 



which the precision is so great, that not only will it register the exact 

 amount of hours, but minutes, primes, and seconds, and even thirds if 

 their frequency could be numerated by us ; and its punctuality is such,, 

 that if two, four, or six of these instruments be taken, they will keep so 

 well together, that there will be no variation between them- not even 

 as much as the beat of a pulse at the end, not merely of an hour, but 

 of a day, or even of a month. I derived the fundamental principle of 

 this machine from an admirable proposition which I demonstrate in 

 my book ' De Motu.' " And then, unfolding the theory of the oscillations 

 of the pendulum, he continues : " The tediousness, however, of being 

 obliged incessantly to count the vibrations can very conveniently be 

 provided against in this wise viz., by arranging that there should pro- 

 ject from the middle of the circumference of the sector, a small, fine, 

 thin pin, that in passing hits on a boar's bristle fixed at one of 

 its extremities, which bristle rests upon the teeth of a wheel, as light as 

 paper, which must be placed on a horizontal plane near the pendulum and 

 having around it teeth like those of a saw, that is, with one of the sides 

 placed at right angles on the plane of the wheel, and the other inclined 

 obliquely ; thus, it will serve this purpose, that when the bristle hits 

 against the perpendicular side of the tooth, it will move it ; but on the 

 return of the same bristle on the oblique side of the tooth it does not 

 move it, but bending over it, slides past and falls at the foot of the 

 following tooth. In this manner, in the passage of the pendulum, the 

 wheel will move for the space of one of its teeth, but at the return of 

 the pendulum, the wheel will not move in the least. Hence its move- 

 ment will be circular, and always in the same direction ; and having 

 marked the teeth with numbers, it will be easy to know the quantity 

 that have passed and consequently the number of vibrations, and the 

 particles of time run. Around the centre of the first wheel another 

 wheel can be adjusted having a smaller number of teeth; which 

 in its turn touches a third larger one ; from the motion of which 

 we shall be able to know the number of complete revolutions of 

 the first wheel, by so disposing the teeth that, for example, when 

 the second wheel shall have made one turn, the first shall have 

 accomplished twenty, thirty, or forty, or as many as you like ; but 

 to explain this to you, who have men most exact and ingenious in 

 the making of clocks and other admirable machines, is quite super- 



