Management of delicate Balances. 345 



as in the case of the balance generally. But if e is less 

 than 180°, an equilibrium can only take place when the mo- 

 ment of D is greater than the difference of the moments of 

 A and B, and when by the increase of A and B the moment 

 of D becomes the leasts the system will overturn or upset as in 

 a balance adjusted so as to i set/ as it is technically called. 



The sensibility of a balance depends upon the moment of 

 D being as nearly as possible equal to the difference of the 

 moments of A and B, as the system is then easiest put in 

 motion. 



To adjust a balance, the points of suspension, and the cen- 

 tre knife edge must first be brought as nearly in a straight 

 line as possible. The arms of the beam must then be nearly 

 equalized in weight by filing. The beam must be made to 

 vibrate slowly and steadily, and if the vibrations are too rapid, 

 the centre of gravity is too low, and it must be raised by 

 screwing up the adjusting ball on the top. If the beam up- 

 sets, the centre of gravity is above the centre of motion, and 

 the ball must then be screwed down. When the beam settles 

 horizontally, or to the zero-point of the scale, it must be revers- 

 ed to see if it will again settle at zero, by which any error in 

 the position of the scale, or the index, is at once detected. 



The beam having been made to vibrate slowly and steadily, 

 the scale pans are then to be hung on, and a weight as heavy 

 as the beam will bear is to be placed in each. Additional 

 small weights are to be placed in the pan which is lightest, to 

 bring the beam to the horizontal position. If the beam up- 

 sets and will not settle horizontally, the screw point supports 

 are to be turned so as to bring the points lower ; but if the 

 beam vibrates too quickly, the points are to be screwed up 

 a little. 



By this the points of suspension are brought nearly into a 

 straight line with the centre of motion, but if it is found that 

 the beam vibrates quicker when loaded, than it does when un- 

 loaded, it shews that the points of suspension are still a little 



