132 Description of a Self-Hegister'mg Tide-Gauge. 



original position in whicli it was set. Supposing the tide be- 

 gan to flov/ when the machine was in this last position, by the 

 float. (/ (fig. 3^\ rising, it would reverse the motion of pulley 

 and pinion, and bring the rack and traversing bar towards the 

 right, or towards high water, on the table. After having left 

 the sliding piece at its position for denoting low water on the 

 9th of tlie month, it is now proceeding towards the sliding 

 piece for denoting high water on the 10th ; and when the 

 bush and pin come to the tongue or switch, the pin moves up 

 the inclined plane and on towards the right, moving the slid- 

 ing piece for denoting high water on the 10th to its right po- 

 sition for that tide. Supposing now the tide to ebb, the ac- 

 tion of the float reverses the wheel, pinion, rack, and travers- 

 ing-bar, and when the bush and pin come to the under side of 

 the tongue, towards the left, the pin Avill lift the tongue by 

 the strain produced by the weight q-, on the cord which is at- 

 tached to the bush ; and having lifted the tongue, and passed 

 on in a straight line, the tongue falls immediately by its own 

 weight after the pin in the bush ^, has passed it ; and com- 

 ing back for the next high water, the pin has to move up the 

 inclined plane as before, and so on with the whole of them. 



The snugs .v, arc for fixing the machine securely by screws 

 to any convenient place for its reception. 



There is another way that might be adopted for the float 

 giving motion to the machine than a cord and pulley (see fig. 

 4.) A vertical rack o, attached to the float to work a spur- 

 v.'heel y, which could be of the same diameter at the pitch- 

 line as the diameter of the pulley /, so as not to derange the 

 other parts and scales. The vertical rack might be more cor- 

 rect in the event of a cord being apt to stretch, which, how- 

 ever, would be obviated with a chain ; but for high tides, say 

 20 or 21 feet, a rack would be very unv.ieldy, for it would re- 

 quire to be equal in length to the highest tides. 



The full size of the registering part of the machine is about 

 2 feet square over al', and 2} inches in depth ; and if made of 

 brass (as iron is apt to corrode from tlie action of the moisture 

 from salt water), the cost of the whole apparatus, including 

 the float and countei-balance, and the pipes in which tliey 



work, I have estimated at about L 30. 



John Maxtox. 

 I.Emi Engine-AVoki:?:, 17'''' ^<'V. 18-12, 



