250 MR. BUNT'S DESCRIPTION OF A NEW TIDE-GAUGE. 



showing the guides N and Q. The outer support S, fig. 2, of the axis of the wheel C, 

 is also removed. 



The cylinder, which is 24 inches in length and 48 in circumference, is composed 

 of mahogany staves 2 inches in width and 1 inch in thickness. It has two heads and 

 \^ a diaphragm, also of mahogany, into which every stave is screwed by a screw at each 

 end, and another in the middle. A strong iron axis passes through the whole length 

 of the cylinder, which revolves on a rounded steel pivot screwed into the lower end 

 of the axis. The surface is a white enamel, fit for receiving the mark of a pencil. 

 On the top is screwed a brass wheel, equal in diameter to the cylinder, and divided 

 into 360 teeth. A two-hour pinion {p) of thirty teeth, at the bottom of the clock face, 

 causes this wheel to perform one revolution in twenty-four hours. This pinion, to- 

 gether with the rest of the train, is seen in fig. 6. 



The clock is of a superior kind, and larger size than ordinary, having a fir pen- 

 dulum rod and a dead-beat escapement. It goes exceedingly well, and appears to 

 suffer no derangement in the regularity of its motion from the incumbrance of the 

 cylinder. This, however, is very trifling, a weight of half an ounce being suflScient 

 to overcome it. The pallets may be detached from the train by lifting a latch behind 

 the clock, and drawing them backwards. This arrangement is required from its 

 being necessary to^^ the hands so that they cannot, as in other clocks, be made to 

 slide without carrying the train along with them. The pinion which drives the cy- 

 linder may be detached from it by pulling it forwards, so as to permit the cylinder to 

 be turned freely round. 



Although the workmanship of the clock is good, yet, from inequalities in the teeth 

 of the wheels, the cylinder is not moved round through exactly equal spaces in equal 

 times. To prevent error from this cause, the hours and minutes marked round the 

 top of the cylinder, were divided out in the following manner. The cylinder being 

 connected with the clock, but the pallets and pendulum detached from it, the hands, 

 which now move rapidly forward, are brought to the instant of 0^ 0™, where they 

 are held fast while a vertical line is drawn on the cylinder, by the pencil moving be- 

 tween the guides. The hands are then moved forwards 20 minutes at a time, and a 

 line drawn on the cylinder at each of these periods, until the whole circumference has 

 been divided into 72 spaces. These are afterwards subdivided to every 5 minutes. 

 Another necessary precaution is, to mark a tooth of the large wheel on the cylinder, 

 and the two corresponding teeth of the small wheel which turns it, and in the same 

 manner to mark all the wheels in the train, so that whenever the clock is taken to 

 pieces to be cleaned or repaired, the wheels may be put together again, with the teeth 

 in exactly the same relative positions as before. By this means, a source of consider- 

 able error is entirely obviated. 



The scale of height may be obtained, by marking the outside of tiie trunk contain- 

 ing the float into feet, and watching the ascent of the surface of the tide until it 

 reaches one of the lower mar^ks, when a mark must be instantly made with the pencil 



