DESCRIPTION OF A RHEUMAMETER. gg 



steelyard, to ascertain the farce of a stream on a given sur- 

 face. His process is analogous to that of the bent lever 

 balance, as described by Michelotti in his work on Experi- 

 mental Hydraulics; but his method is not so simple, nor 

 his apparatus so cheap and portable, as that of Mr. Gau- 

 thier. 



I have observed however, that the hand which holds the Improvement 

 rod, to which the instrument is tixed, is liable unintention- J-JjJ,''' ^^'^^ ^^^ 

 ally to give it an additional impulse. This incouvenit^nce 

 has led me to employ the steelyard in a difiereut manner, 

 which appears to me more convenient and more accurate, 

 and affords the double advantage of measuring in distinct 

 manners both the velocity of the current, and its absolute 

 force on a given surface, so that the two modes of exami- 

 nation mutually check each other. 



The apparatus consists of a cork log, or float, 10 cent. Apparatus Ce 

 [4 inches^ square, in the shape of a cube, so ballasted as ^^"°^*** 

 just to sink to the level of the surface. A small reel, turn- 

 ing very freely, on which is wound a silk cord of a given 

 length, to measure the distance the log should float. A 

 small dynamometer, resembling that I constructed to mea- 

 sure the strength of threads of silk, cotton, or flax. With 

 this apparatus, which may be carried in the pocket, the 

 action of a current may easily be ascertained. 



To the upper part of the log is fastened a silk cord, 

 forming an acute angle, like the string of a kite; and to the 

 point of the angle is hooked a red string two yards long, 

 tied to a green string ten yards long, which is entirely 

 rolled up on the reel. The other end of the green string 

 is fastened to the reel, which the observer holds in his hand. 

 A cord of two colours is used, to distinguish the part in- 

 tended to measure the distance passed through from that 

 which should be in the water with the log. 



I have preferred a silk to a hempen cord, not only be- 

 cause silk is stronger and mtore pliable, but because it does 

 not twist in the wat€r, and retard the progress of the log* 

 To satisfy myself of this, I have thrown into the water littl« 

 pellets of paper, which floated freely by the side of the log; 

 and the eye could perceive a sufficient uniformity in a dis- 

 tance of ten yards, the measure fixed on. 



To 



