HOROLOGY. 



merits of thin brass, having the same radius as- the 

 wheel, and cutting them from the proposed number on 

 the cutting engine, will lead us to form an idea of the 

 strength that the teeth may have. Indeed this, and 

 calculation together, ought to go hand in hand, and is 

 the way that any ingenious clockmaker ought to adopt, 

 if his object is to have the best possible contrivance in 

 the construction of any piece of work in which he may 

 be engaged. 



If it is proposed to have the pendulum of such a 

 length as to swing 30 beats in a minute, the swing- 

 wheel having 30 teeth, and the pinions 10 each ; then 

 the numbers for the teeth of the second and third 

 wheels will be 60 and 50, and the length of the pen- 

 dulum 156.8 inches; where twenty feet or upwards, 

 for length of fall and strength of clock can be ob- 

 tained, a shorter pendulum than this should never 

 be adopted. The diameter of the second wheel may 

 be made half of that of the great wheel, or even 

 a little less; however, we may safely take it at the 

 half, viz. 7-6 inches, as it is to be cut into half 

 the number of teeth, and being considerably thinner 

 than the great wheel, the teeth will, notwithstand- 

 ing this, be sufficiently strong for the force exert ed n 

 them. The third wheel having 50 teeth, and the force 

 exerted on them being considerably less than that on the 

 second wheel, we may obtain the diameter of the third 

 wheel, by first taking the proportion of 60 to 50, and 

 then making the diameter somewhat less than the first 

 proportion would give, because, were the teeth cut on 

 this diameter as given, they would be as strong as 

 those of the second wheel. We then say, as 60 teeth 

 is to its diameter of 7.6 inches, so is 50 teeth to the di. 

 ameter required, which is found to be six inches. 

 Taking six inches in the compasses, and applying them 

 to the legs of any sector that has a line of equal parts, 

 both legs of the sector being extended till the points 

 of the compasses fall exactly on 50, set the compasses 

 to the number 45, which will give a distance equal to 

 the diameter of the third wheel. This will be found to 

 be 5.5 inches nearly, and if the swing wheel is made 

 five inches in diameter, it will do very well. 



The barrels both in the going and striking parts be- 

 ing made equal in diameter, and each performing a re- 

 volution in 12 hours, we now proceed to make out 

 proper numbers for the striking part and diameters for 

 the great wheel, the pin wheel, and the tumbler wheel; 

 this last we shall also make use of as a fly wheel. The 

 diameter of the barrels being equal, the great wheels 

 may also be equal, and the diameter of the striking great 

 wheel will be 1 5.2 inches. The number of blows which 

 the hammer must make in 12 hours, can be obtained by 

 a very simple rule. The first blow 1 being added to the 

 last blow 12, will make 13, and 13 multiplied by 6, half 

 of the number 12, will give 78 for the number of 

 blows required during one revolution of the great 

 wheel and barrel. The great wheel of the striking 

 part will require to have rather stronger teeth than that 

 of the great wheel of the going part, because there is 

 a stronger rope and a heavier weight applied against 

 them, in order to raise as much weight of hammer as 

 may be, so as to bring a sufficient sound from the 

 clock bell. The pin wheel pinion being 10, and the 

 wheel 64, having eight lifting pins in it for the ham- 

 mer tail, the number of teeth in the great wheel which 

 will be necessary, so that one turn of it may produce 

 78 blows, may be either 98 or 100. 



Suppose we take 98 for the number of teeth, 98 di- 

 vided by 10, the number in the pin wheel pinion, the 



quotient will be 9.8, which, multiplied by 8, the num- Turret 

 ber of pins in the pin wheel, will give 78.4 for the Clocks, 

 number of blows for one revolution of the great wheel. "^~~ - 

 If the great wheel should have 100 teeth, this, divided 

 by 10, will give 10, and this again multiplied by 8, 

 will give 80 for the number of blows during one turn 

 of the barrel ; either of these numbers for the teeth of 

 the striking great wheel would do very well. If wo 

 take 98, and as the pin wheel is to have 64 teeth, we 

 may find a proper diameter for it, so that the teeth 

 may be nearly about the same size as those of the great 

 wheel. Say as 98, the number of teeth in the great 

 wheel, is to 15.2 inches, its diameter, so is 64, the num- 

 ber of teeth required in the pin wheel, to a diameter re- 

 quired for it, which will be found to be 9.9 inches. 



The pin wheel, having 64 teeth, and 8 lifting pins 

 in it, the tumbler wheel pinion, which makes one re- 

 volution for every blow of the hammer, must have 8 

 teeth or leaves in it. The diameter of the tumbler 

 wheel must be considerably smaller than that of the 

 pin wheel, and this will depend on the number of teeth 

 it ought to have, on the number of leaves in the fly 

 pinion, and on the number of the revolutions which the 

 fly pinion is to make for every blow of the hammer. 

 The less the number of revolutions given to the fly pi- 

 nion during one blow of the hammer, the less will the 

 striking part be under the influence of oil. But few 

 turns in the fly require it to be considerably extended 

 in the wings or vanes, and this demands some ingenui- 

 ty and address in the clockmaker to carry them out, so 

 that they shall be conveniently clear of every part of 

 the clock. When the arms of the fly are extended, the 

 wings or vanes can be considerably diminished in sur- 

 face ; and a little weight may be given them, so that 

 when once the fly is set in motion it will not easily 

 stop. The construction of the fly, and. fly pinion, has 

 hitherto been injudicious. The flies commonly ap- 

 plied to turret clocks were too heavy, the wings or 

 vanes were too broad, they made too many revolu- 

 tions, and the fly pinion was not so properly sized as 

 it might be : for it must be considered that it acts not 

 merely as being driven, but it must sometimes act as a 

 leader. For although the tumbler wheel, or fly wheel, 

 which turns the fly pinion, acts as a driver, yet, from 

 the nature and application of the fly pinion, and fly to 

 regulate the velocity of the striking, the fly pinion, 

 from the acceleration which it will acquire, must some- 

 times act as a leader, so that the size of the fly pinion 

 ought to be a mean between the size of a leader and 

 that of being driven. If the pinion is made too large, 

 or the size of a leader, the wheel teeth in driving it 

 would be apt to butt on the pinion, and if made too 

 nicely, as it were, to be driven, it could hardly ever 

 act as a leader, as here the pinion would butt on the 

 wheel teeth ; this then is the reason of keeping it to the 

 mean size of the two, which will be found to have a good 

 effect. The arms of the fly may be about twenty-six 

 inches. 



The number of the revolutions of the fly pinion for 

 one blow of the hammer is arbitrary ; in some clocks 

 the fly may make twenty revolutions, in some more and 

 in some less- When the' revolutions are few, and the ac- 

 celeration of the fly fit to carry forward in a small de- 

 gree the striking, it may appear to strike faster to- 

 wards the end of a long hour, but it will require a 

 nice ear to perceive it. We have made the fly pinion to 

 have only four turns for one blow of the hammer, which 

 answered extremely well, so that the tumbler wheel 

 will require 40 teeth, supposing the fly pinion to have 



