350 On the Construction and 



This i bob balance* I have found practically to answer most 

 satisfactorily, and the only inconvenience is, that the mea- 

 sure of its sensibility is constant, and whether the weight 

 estimated is large or small, yet still the error in the result 

 is always a fraction of the weight to which the beam is 

 adjusted. 



Practically this inconvenience is not so great as might be 

 supposed, the substances to be weighed in the investigations 

 of analysis being generally of nearly the same weight as 

 when in the shape of powders or fluids they are generally 

 contained in vessels in which they have been exposed to the 

 action of heat, &c. to prepare them for the correct estima- 

 tion of their weights. 



However, this objection may be in great measure removed 

 by having a number of i bobs' of different weights fitted to the 

 beam, which are readily put on, and then a few turns of the 

 adjusting ball gives the requisite slowness to its vibrations, 

 and thus the balance is readily prepared in a few minutes for 

 weighing light substances, or for adjusting weights whenever 

 it becomes necessary. 



The beam of an instrument which I have fitted upon this 

 plan, is 13 inches in length. The scale pan-arm being 7 in- 

 ches long, and the bob-arm 6 inches, and it is 3 inches 

 wide in the centre, tapering off to each end. It is cut out 

 of a plate of steel Lth inch in thickness, and all the central 

 part is removed except a cross support and two circles 

 which strengthen the arms, leaving a very light frame 

 about Hth inch in width. As this would bend a little when 



10 



held by one end with a ball of 3000 grains weight at the 

 other, the requisite stiffness is given by soldering on to the 

 lower edge a thin steel strap of \ inch in width. This is ef- 

 fected by cleaning the surfaces to be joined by a solution of 

 sal ammoniac, and tinning them. The strap is then bound on 

 by a number of pieces of twisted brass wires, and some soft 

 solder and resin being applied along the joint, the soldering 



