280 Mr HARRIS'S Experimental Inquiries concerning 



change in the altitude of the water, in consequence of the im- 

 mersion or emersion of a small portion of the cylinder W, does 

 not sensibly influence the indications on the arc MIN. 



7. The cylindrical counterpoise just mentioned is made of fine- 

 grained mahogany : it must be turned very accurately, and must 

 be perfectly free from grease or varnish of any kind, so that be- 

 coming readily wetted by the water, it moves in it with great free- 

 dom. The body of this counterpoise is from two and a half to three 

 inches in length : its lower extremity terminates in a short stem 

 p, on which is fastened a brass ferule, having a screw at its lower 

 part, by which means a small hollow ball of brass 6', from three 

 to six-tenths of an inch in diameter is attached to it, being 

 previously so loaded as to balance the suspended body x, and 

 bring the index bl within the range of the arc IN, when the 

 lower half of the cylinder W is about one-half immersed in the 

 water. The upper extremity of the counterpoise terminates al- 

 so in a short stem at o, and in a small hemispherical cup ; this 

 cup is intended to receive the additional weight requisite to 

 bring the index to zero ; and thus, by means of some fine shot, 

 which are very convenient for the purpose, the index may be 

 regulated with great precision *. 



8. It appears evident from the nature of this arrangement, that 

 the gravity or weight of the body x being as it were destroyed 



* It is requisite to have several of these cylinders of different diameters, namely, 

 from 0.2 of an inch, to an inch, each increasing in diameter about 0.1 of an inch. 

 They should be very accurately turned, and, before being used, should be freely 

 wetted throughout their whole length, which is best effected by allowing them to 

 remain for a short time immersed in water as high as the upper stem. They are 

 suspended in their situation by means of a loop of silk, inserted in the bottom of the 

 hemispherical cup into a small hole drilled through its centre into the stem, and se- 

 cured there with a small peg of wood in the way already described in note on p. 279- 



