II! 



HOROLOGY. 



ipiinn 



o!' an I'ljn.v 

 tion i : 



Mechanism 

 fur shewing 

 the day of 

 the m<mih 

 without any 

 shifting, ex- 

 cept in 

 leap years. 



very tedious and nice operation ; ibr this purpose 

 the rack, ami all the wheels immediately connected 

 with tin- equation, must be put into their places, as also 

 all those which {jive motion to the annual plate, and to 

 h.-ive a spring tight arm, having a sharp point to it, 

 l>c:irin;j on tin- face of the brass plate which is to be the 

 elliptic one : the sh::rp point must lie so as to coincide 

 with the side of the steel pin, when bearing on the 

 rdge of the elliptic plate. The sun and minute hands 

 being on. and the annual plate set to the 1 st of January, 

 the equation hand set 'to the equation for that day, then 

 !>y setting forward the minute hand until 12 or 2+ 

 hours have elapsed, the equation hand may be changed 

 to what it ought to be, in the same time ; so by going 

 on step by step in this way, the figure of the equation 

 plate may be truly done. The rack must be artificially 

 made to assist in this ; and when the revolution is com- 

 pletely at the end, before taking out the rack and the 

 equation wheels, marks must be made to one of those 

 teeth, which must be marked by its corresponding 

 space in the other wheels, so that when they are again 

 put into their places, they shall give such equation as 

 was done when tracing for the elliptic plate. 



Besides the days of the month, which are shewn on 

 the annual plate, there is a common month ring, having 

 .')! figures engraved on it, placed as usual at the back 

 of the dial. One of these figures is shifted every day 

 through the whole ring when the month consists of 31 

 days ; and two figures at the last are shifted at once 

 when the month consists of 30 days, to bring the ring 

 to the first day of the succeeding month ; and at the 

 28th of February four figures are shifted, so as to bring 

 the ring to the 1st of March : by this means the day of 

 the month ring requires no shifting or correcting at 

 these periods, as those in the common way do. To 

 produce this motion, five short steel pins are placed in 

 a circle, on the under side of the elliptic plate, whose 

 radius may be about half an inch, and set at such a dis- 

 tance from one another as to correspond with the num- 

 ber of days between February and April, between April 

 and June, between June and September, between Sep- 

 tember and November, and between November and 

 February. This may be done by applying the elliptic 

 plate on a cutting or dividing engine, having the num- 

 ber 565 on the dividing plate. When fixed on the en- 

 gine, and set to the first point of the number, make a 

 point for February on the elliptic plate, then count off 

 <>'! from the dividing plate, which will give the place 

 tor th pin on the 30th of April ; another 61 will bring 

 it to June 30th ; 92 will give the 30th of September ; 

 6'1 the 30th of November ; and 90 more will bring it 

 to the 28th of February, the point -which was set out 

 from. When the pins are put in the elliptic plate, that 

 for February will require to be longer than the others, 

 for a reason which will be explained when we come to 

 shew the use of these pins. The month-wheel of 84 

 teeth, and whose diameter is 2.75 inches, has its centre 

 on the left hand side, distant from the central perpendi- 

 cular line 1.4 inch, and from the centre hole in the fore 

 frame plate 2 inches. The month wheel, as usual, is 

 turned about by the month nut. A long piece of brass 

 forming two arms, each four inches in length, has a 

 small arbor through the middle of the "whole length of 

 eight inches. The pivots of this arbor run into small 

 cocks, attached to the front of the fore plate, keeping 

 the long piece of brass very near to the plate ; indeed a 

 great part, particularly the end of the upper, arm, and 

 towards it, is sunk partly into the fore plate. This long 

 piece of brass is placed so that one of the arms shall 

 come to the socket of the month wheel, and the other, 



Equation 

 Clocks. 



tion clock. 



with its end nearly below the circle in which are the 

 five pins, in the annual elliptic plate described as before. 

 A spring is placed below this upper arm to keep it up, 

 unless when any of the pi"" g et on the end of the arm 

 and press it down The end of the arm is chamfered, 

 or made s that any pin, when approaching it, gets easily 

 D.., and presses it down gradually, by means of ascend- 

 ing the chamfered part as it were ; and when past this, 

 it meets with a flat and very narrow place, where it 

 cannot remain longer than sometime short of 24 hours, 

 say 16 or IS hours, or perhaps not so long. After hav- 

 ing passed the flat part, it meets with ^chamfered side 

 opposite to that of the first. Besides that of freeing the 

 pin, this is made for the purpose of more easily setting 

 back or forward the annual plate. 



The month wheel has its socket equally long on both PLATE 

 sides, snd quite straight; the length of each may be .(> ro:iv. 

 or .7 of an inch. Two small brass pillars are rivetted *''** 8> 

 on the upper side, and opposite one another, each at a 

 distance from the centre of the wheel about .7 of an 

 inch, (see Figs. 8, 9.) the height of the pillars from the 

 wheel to the shoulder about half an inch ; and from the 

 shoulder of each pillar a sort of straight pivot is pro- 

 longed, about one half inch more ; the diameter of these 

 pivots about one-tenth of an inch ; that of the pillar .2 

 of an inch. There is another socket which goes easily 

 on the lower or under socket of the month wheel, which 

 is rivetted in a rectangular piece of brass, about an inch 

 long, and half an inch broad, or nearly so, say .4 of an 

 inch. In this piece of brass, on the side opposite that 

 of the socket, are also rivetted two small and straight 

 brass pillars, about an inch in length, and the diameter 

 about one-tenth of an inch. There are holes in the 

 month wheel, to allow these pillars to go easily back 

 and forward in them ; their places will be equally be- 

 tween the month wheel socket and the pillars which 

 are rivetted in the month wheel. The other ends of 

 the small straight pillars are made fast, by two small 

 steel screws, to a piece of brass, which is formed to cor- 

 respond with two broad crosses of the month wheel. 

 Only one of them is made to have at the end a segment 

 of a circle, whose radius is nearly equal to that of the 

 month wheel. On this segment three teeth are cut, 

 equal in their spaces and form to those of the month 

 ring. In the arms or crosses of the segment are three 



holes, One Of Wllicll J^oca easily ovor or on tlip upper SOC- 



ket of the month wheel ; the other two holes go easily 

 on the small straight pivots which have been already 

 mentioned. This segment cannot be put on the ends 

 of the small pillars, till the socket of the rectangular 

 piece of brass is put on the lower socket of the month 

 wheel, having previously made the pillars connected 

 with it to pass through their holes in the month wheel. 

 It will be easy to perceive, that when the segment is 

 put on to its pillars, and a sufficient space left behind 

 the month wheel and the rectangular piece of brass, 

 its socket may be made to pump up and down on that 

 of the month wheel, and at the same time carrying the 

 segment back and forward with it ; a pin in the month ' 

 wheel stud keeps the month wheel socket always to its 

 proper end shake, notwithstanding any motion of the 

 segment backwards and forwards. Below the rectan- 

 gular piece on its socket, a small groove is turned out 

 of it, for the purpose of a forked piece getting in on it ; 

 this forked piece is formed on that end of the arm 

 which lies along the fore plate, and on to the socket or 

 centre of the month wheel. 



From the preceding description, it is evident that 

 when any of the elliptic plate pins come to press down 

 that end of the long arm which lies near and under 



