Volume V

128 PHILOSOPHICAL PAFERS.I have tried in a sailing boat, with all the varieties of motion theboat was liable to, the result of the contrivance, with a tube of twoinches dii.meter and pipes bored from a twelfth to a quarter-inch,without perceiving any other difference than in the times of the riseand fall of the water in the tube.A slup would occasion greater pressure from pitching than a boat,from the greater distance between the hole and the centre of gravity ;though the slower movements of the ship would nearly counterpoisethe effect of the unequal distances from the centres of motion.If a float within the tube be fitted with a small line and weight, tokeep the line strait, moving freely over a brass pulley up and down agroove for the purpose, and a scale be marked below thepulley, fromthe calculated table, on the outside of the tube, or other case madefor the purpose, with a movable index on the line, only beginning thescale from o to eleven miles downwards, inversely,as the table, andthe indt-x be placed at o, or the beginningof the scale, when the shiphas no diredl motion ;whenever the ship acquires a velocity the floatwill ascend, and consequently the index descend, to the mark denotingthe rate of sailing.If the hole in the pipe under the ship's bottom was in the afte*part of the pipe,the water would descend in the wooden tube as muchbtlow the surface, as it ascends above it with the hole forwards: thepressure due to the velocity being then minus.This is the most convenient mode, when the following contrivanceis not in addition.CONTRITANCE to determine the Quantitysailed in agiven Time.ASSUME a point on the after part of the wooden tube,supposedin the plane of the ship's flotation, when the shipis in lightest sailingtrim ;at three or four inches below that point make a mark, andwith the distance between deep and light load water-line, make asecond and lower mark.Betw een the marks attach a small pipe or tube of wood, an inchor an inch and a quarter in the clear, closed at the lower end, andcommunicating with the larger tube by a small pipe.The length ofthe attached tube, for all ships of war, may be three feet.Within this attached tube, through collars of leather, are twosmallci coppe- pipes, to move up and down conformably to the ship'splane of flotation.At the lower end of the least of the iscopper pipes, bored a-capillary hole of the thirtv-secon ' of an inch diameter, or else aglass end with capillary bore as above. This size is chosen merely