'176 PHILOSOPHICAL TRANSACTIONS. [aNNO 1726. 



Dr. D.'s contrivance therefore is a machine, which will carry down Mr. 

 Hales's gauge to the bottom of the sea, and immediately bring it up again : as 

 represented fig. i, pi. 6. ab is the gauge bottle; pf the gauge tube, cemented 

 to the brass cap of the bottle at g, with its open end f immersed in the mer- 

 cury c, which by the pressure of 32 feet of water is carried up to d, with a little 

 treacle or honey d upon it, raised up from d, a small thickness of treacle poured 

 on the mercury. When the pressure of water is from a depth of 64 feet, the 

 mercury and treacle rise up to e, |- of the height of the tube ; and so higher 

 proportionably to the depth. 



N. B. A scale may be marked on the tube with a diamond. 



K represents a weight, hanging by its shank l in a socket m, fixed to the 

 ring MB, cemented at the bottom of the bottle. When the hole l of the shank 

 is shoved up to m, the catch 1 of the spring s holds it from falling out of the 

 socket, while the machine is descending. But as soon as k. touches the ground 

 at the bottom of the sea, the hole l rising, the catch flies back and lets go the 

 weight, as represented in the figure. Then the empty glass ball i (which at sea 

 may be a hog's bladder) rises up to the surface of the water with the machine ; 

 in which observing how high the inside of the tube is daubed, the pressure, 

 and consequently the depth of the sea is known. 



KG represents a brass tube to guard the top of the gauge tube. 



There are holes at f, g, and e, to admit the water to pass freely every 

 way. 



To confirm the use of this sea-gauge, Dr. D. made an experiment in the fol- 

 lowing manner. Having poured some quicksilver into the bottle of the gauge, 

 he poured on it treacle to the depth of half an inch; then screwed on the brass 

 cap of the bottle to which the glass gauge-tube was cemented ; by which means 

 the open end of the tube was brought under the surface of the mercury, the 

 sealed end being upwards. The machine, thus fitted, was immersed in a cylin- 

 dric vessel of water, which with a plate at top was pressed between two columns, 

 in such manner, that air might be condensed over the water without escaping. 

 Then having forced in so much air with a syringe, as to lay on a pressure equal 

 to what would be in a depth of 40 feet of water, he opened the cock of the 

 upper plate, let out the air, and, on taking out the machine, it appeared how 

 high the quicksilver had risen in the gauge-tube, by the smeared mark which 

 the treacle left within. 



