1835.] Balances for Delicate Weighing. 87 



one grain to ten thousand. They have one support and one 

 glass case in common to them ail : the beams not required 

 are kept in a box fitting in at the back of the glass case, so 

 that they are always at hand. Fig. 12 is a perspective sketch 

 of the case with one of the balances mounted. The figure 

 jSpeaks for itself. — =It has a glass slide to close the front, 

 and the usual contrivances of an assay balance for reli eving 

 the beam and scale pans, and for adjusting the level. 



4. The most delicate balance that I have is used for 

 weights not exceeding 10 or 20 grains. It is made simply 

 of a piece of well seasoned, clean, straight grained fir ; and 

 figure 1 is a representation of it. The knife edge works on 

 a plane of agate ; it is made of steel and was tempered as a 

 workman would say " dead hard," being afterwards very 

 carefully sharpened on a hone, and examined by a micros- 

 cope. The edge is a perfectly straight line, smooth, well 

 defined, not wiry, not a sharp cutting edge but rather slight- 

 ly round, so that it may be firm enough to withstand the 

 wear and tear that may be required of it, and yet be nothing 

 more than a line, presenting no resistance, but acted on 

 when in the beam by the slightest weight. Figure 2 repre- 

 sents the fulcrum and the centre part of the beam of the 

 real size : the brass a, is screwed down by the screws b, b 

 having a plate of brass c, under them to prevent the heads 

 penetrating the wood. The beam d, is notched out for the 

 fulcrum e, to lay in, and the brass a, very securely fixes it in 

 its position, care being taken that the notch is made at a right 

 angle, and that it is not too deep. The fulcrum should por- 

 ject a little above the beam so that the securing brass a, may 

 press firmly upon it. The points a, a, fig. 1 were put in at 

 as nearly equal distances from the centre as could be mea- 

 sured by a pair of compasses ; for I did not intend the beam 

 to be a balance of perfect equipoise, knowing the extreme 

 difnculty of adjustment to quantities so minute as y oVot^ 

 or -3 oVoth part of a grain. 



5. Fig. 3, shews one end of this balance of the real size. 

 The point a, is a piece of hardened steel wire with a screw on 

 it, screwing up tight through the wood of the beam b, and 

 being further secured by the tightening nut c. The point is 

 exiremely firie and sharp, but carefully made, and proved or 



