1835.] Balances for Delicate Weighing. 89 



giving it a good hearty shake because its indications were 

 sluggish." The least accident deranges so delicate an 

 instrument ; the slightest breath of air^ a particle of dust^ or 

 unskilful management. The difficulty in delicate weighing 

 is to make a balance always agree with itself, which it will 

 not do unless it is in perfect order, and unless it is under 

 the sole care of one who is completely master of its peculi- 

 arities. Few practical men who have a good balance like 

 another to use it. 



9. I must add that the way to use this balance is this : 

 -suppose you wish to ascertain the accuracy of a given weight, 

 ^^lace a known accurate weight in the right hand scale, and 



quipoise it by counterweights in the other. When perfectly 

 quipoised, take it out and put in the v/eight you wish to 

 ^rify^ then if on the second trial an equipoise is produced, 

 two weights are equal. Or if you wish to ascertain the 

 , -ct weight of any small substance, place it in one scale 

 f ^ balance it by counterpoise weights in the other: remove 

 J^S.cl by real weights produce an equipoise and the true 

 at results. This is in fact the only accurate method of 

 ^^??|hing^ for the best balances are seldom perfectly correct^ 

 ^^kicularly after they have been in use for some time.-— It is 

 very difficult to adjust delicate balances so as to be perfect 

 ■ equipoises, though the adjustment may be made so very 

 near the truth as to be a matter of no consequence for any 

 ordinary practical purpose. 



10. My second balance weighs any quantity not exceeding 

 200 grains and indicates to the ToVath part of a grain. Figs. 

 5^ and 6, represent the central portion, and the index end 

 of this balance of the full size. The length of the beam is 

 the same as in Fig. 1. — The general construction is the same 

 in principle as the balance just described, but being design, 

 ed for more frequent use the beam is made of steel, which 

 by means of linseed oil put on it and burned off over a fire 

 was blackened and covered with a sort of varnish that pre- 

 vents its rusting. The fulcrum is a piece of square steel vare 

 made dead hard by heating it cherry red, and plunging it into 

 cold water. Then as in the former case working it to a 

 ^proper edge on the hone. In fig. 5, a, is a piece of brass 



