145 
of Edinburgh , Session 1875-76. 
form only in two points, of which the more important is a modifi- 
cation of the centre of gravity “ bob” arrangement, which enables 
one, at a moment’s notice, to shift the centre of gravity of the 
instrument from a certain definite position, I., to .a certain 
other (higher) position, II., matters being arranged so that in 
passing from I. to II., the sensibility, i.e. the deviation, correspond- 
ing to an overweight of, say 1 milligramme, is increased in an 
exactly pre-determined ratio, such as of 1 : 10, for instance. For 
this purpose the “bob” is made very light, so that the distance 
through which it has to travel in order to effect the desired change 
of sensibility is not too small, and, instead of to a screw as usual, 
is fixed by mere friction to a vertical triangular steel rod forming 
part of the needle. The other new feature in the balance is, 
that the rider-principle, besides being discounted in a slightly 
different manner from the customary one, is extended to the 
determination of differences of weight up to 100 (instead of 10) 
milligrammes. 
The arrangement adopted is represented in the accompanying 
sketch, for the interpretation of which it is only necessary to say 
that C (10) and (10) O are equal to C (0) x and (0) 1 (10)j respectively, 
and that both O (10) and (10)j are each divided into 10 equal 
parts, the former by notches filed into the beam, the latter by 
marks ; and to add, that there are two riders, one weighing^ centi- 
grammes for the left arm, and another weighing p milligrammes 
