404 PHILOSOPHICAL TRANSACTOINS. [aNNO 1747. 



if it be found inconvenient to make the arm au so long, as to make very minute 

 alterations in the length of the rod ab easily observable, this inconveniency may be 

 readily removed by having a second bar ef, turning on the axis g, whose arm gE 

 bearing up against the extremity d of the first bar or lever, will rise with it, or 

 be pressed down by it; and the other arm gp being lengthened at pleasure, the 

 arch pf will be as large as you find convenient; or even a 3rd and 4th lever may 

 be added. 



The instrument, as executed by Mr. Jackson, in the year 1736, on the 

 advice of Mr. Graham and Mr. Ellicot, is represented in fig. 2 and 3. 



In fig. 2, AB is a round rod of steel or brass a quarter of an inch thick, and 

 3 feet 1 inch long: when the rod is of brass 3 feet long, the point a must be of 

 steel 1 inch long, to prevent its wearing away, or losing its point; which conical 

 point is made to screw on and off. cd, cd, are two iron supporters, joined by 

 a flat cross bar at bottom od 2 inches long, in the middle of which is a point -i- 

 inch high under b, which goes into a hole at the bottom of the rod b, and serves 

 to keep the rod in its place at bottom, as the cross bar ** having a hole in it, 

 through which the rod passes, does in the middle or about ^ up the supporters, 

 and the point a goes into a small hole in the under side of the lever; all which 

 keep the upright rod firm and steady in its place. The iron supporters are flat, 

 or parallel to the front of the machine from c to x and c to x, where they are 

 twisted half round, so that the lower parts xd, xd stand at right angles with the 

 upper parts. This contrivance gives the fi-eer access to the rod for the sand or 

 fluid into which the machine is set to measure its heat, the supporters standing 

 2 inches asunder at od; and that the degrees of heat may be compared uniformly 

 in different experiments, the bottom of the rod must always be immersed to the 

 same height in the matter to be examined; and therefore he made a mark, a 

 small flirrow -jf quite round the rod, 1^ inch fi-om the bottom b. For the deeper 

 the rod is immersed into any matter, it will be lengthened the more by the same 

 degree of heat. 



EF is the lever, which turns on an axis g. At p is fastened a string, which, 

 passing twice round the small pulley h, has a weight i hanging to the other end 

 of it, of about 4- lb. being enough to keep the string always stretched. At the 

 other end e of the lever is hung another weight l, which must be heavy enough 

 not only to counterbalance the longer arm gf, but press down on the point a 

 with a weight sufficient to keep it steady. 



MNO is the back part of the plate, like the dial plate of a clock made of brass, 

 the front of it being as in fig. 3. The pulley h turns on an axis c in fig. 3, 

 which goes through the plate, and on the other side or front of the dial plate 

 caiTies a hand or index ab. 



N. B. G being the fulcrum of the lever, fig. 2, the distance ga being very 

 small, and the distance gf being very great, the smallest motion at a will pro- 



