Description of a i^elf-RegisterinQ Tide-Gvanc. 131 



tides. From the mechanism of the maehme the studs on the 

 right hand of the centre or zero line are for registering the 

 height ; and those on the left the lowness of the tides as 

 measured from the half-tide level. The figures on the right 

 and left margins correspond to the days of the month ; and 

 the drawing represents a register for twenty-eight days' tides, 

 or one lunar month. In figs. 1 and 3, / is a pulley with a 

 cord or small chain passing round it ; to one end of the cord 

 is attached a float g (fig. 3,), and to the other end of the cord 

 is a weight h (figs. 1 and 3), which acts as a counter balance 

 to the float. On the axle of the large pulley /, is a pinion r, 

 and the smaller the diameter of the pinion is, in proportion 

 to that of the pulley, the narrower and more compact the re- 

 gistering plate or table (fig. 1) will be. Letter j represents 

 a rack ; the number of teeth and revolutions of pinion .r, dur- 

 ing the whole range of tide, determining the length of the 

 rack and the proportion of the scales of feet and inches at the 

 top and bottom of the registering plate (fig. 1.) Connected 

 with the horizontal rack j, is a vertical guide or traversing 

 bar /, which is made to move the whole breadth of the table 

 by its rack and the pinion. At the top and bottom of the 

 vertical bar are pullies w?, for running along the guide-rods n. 

 In the vertical bar there is a groove, in which the sliding bush 

 z, is made to move freely v.p and down ; to this bush is at- 

 tached a cord, passing over the pulley p^ at the upper end of 

 the bar, and a constant strain is kept on the cord over the pul- 

 ley by a weight 9, to jirevent the bush *, from falling downwards. 

 In the bush r is a pin which projects into the dovetailed grooves, 

 between the feathers h, and slides easily along in them, as the 

 bar / traverses either way. This pin moves the studs cc, to tlieir 

 proper places for indicating high and low tide. Letter r, as will 

 be explainedpresently, representsmoveable tongues or switches, 

 having joints at one end, so loose, that when lifted they will fall 

 doA^Ti again by their own w-eight. 



We shall suppose that the machine has registered the tides 

 as far as the second tide, on the 9th of the month, as shewn 

 in the diagram (the studs below this being all shewn as moved 

 to their places, and those in the upper grooves remaining un- 

 moved\ and that the tide on the 9th has fallen 7 feet from 

 the datum line (marked on the scale), to this position, there- 

 fore, the pin in the l)u.-h ;- las moved the sliding stud from the 



