VOt. XLIV.] PHILOSOPHICAI, TRANSACTIONS. 405 



duce a very great one at p, and therefore the index will turn very sensibly on the 

 plate. 



The proportions of the rod and lever are discretionary ; his rods, both of steel 

 and brass, were 3 feet long in one solid piece, but they had each a point or cone 

 of steel 1 inch high, that screws on the top at a. The lever has 4 inches from 

 E to A, l-L inch from a to g, and 12 inches from g to p; the distance of g 

 above c is H inch, the brass pulley h is -|- inch diameter; all the other parts of 

 the machine are of oak. The main support or pillar pg is 1 inch square, 2-1. 

 feet high, and at bottom is let through a groove at o. made in a large heavy block 

 or pedestal of wood rs. In this groove the pillar may be raised higher or lower 

 to adjust the height of the pillar to the situation, which the bottom of the rod 

 AB may require in different experiments; and it is to be fixed in that place by a 

 screw at t, which goes through the front of the block, and presses against the 

 bottom of the pillar. 



Fig. 3 represents the dial plate, or front of the plate marked mno in fig. 2. 

 It is a plate of brass, with strong paper glued on it, and may be of any size, Dr. 

 M.'s is 1 1 inches over, ab is the hand or index, which slips on very stiff on the 

 axis c, that carries the pulley h in fig. 2. The outer circle is to be left wide 

 enough to contain the chemical characters or marks to be made on it; the arch 

 DE contains the divisions of Fahrenheit's mercurial thermometer; and the arc 

 PG those of Reaumur, or the spirit of wine thermometer. 



To adjust this instrument for use, place the bottom of the rod b in fig. 2, 

 immersed up to the mark -)- in cold river or rain water, in a vessel proper to be 

 set over the fire ; and when it has boiled for a quarter of an hour, turn the index 

 ab in fig. 3, till it stands in the horizontal position, as at b, being the point of 

 boiling-hot water, and which answers to division 212 on Fahrenheit's arch. 

 Then take it out of the water, and dry it, by holding it a little over the fire: 

 and now great care must be taken, that nothing alters the situation of the index 

 on the axis, a nut to screw on the axis at c may be a good way to keep it fixed. 

 If the instrument be left to cool in the air, the index will fall below b, showing 

 the degrees of cold, or less heat than boiling water; and if put into melting tin, 

 lead, &c. it will show the degrees of heat above boiling water. A brass rod 

 will serve for an instrument to measure the greatest degrees of cold, and all the 

 degrees of heat, to the melting of silver or gold, but to make one to measure 

 greater degrees of heat, the rod must be of steel, or the finest iron. A rod of 

 brass, according to Dr. Muschenbroek's experiments, was found to lengthen 377, 

 when one of iron lengthened only 230 parts. An iron rod, being regulated by 

 boiling water as above directed, will measure not only the heat of melted tin and 

 leatl, but of silver, gold, and copper, and will even show the degree when iron 

 itself begins to melt, which will be the greatest degree of elongation of the ro4 ■• 



