A SIMPLE BALANCE. 



after a few oscillations. If it falls four divisions, it is evident that the sub- 

 stance weighs four milligrams. Taking a rather thicker platinum wire, to 

 which a shorter lever must be adapted, one can weigh the decigram, and 

 so on. It would be an easy matter, also, to make, on the same model, 

 balances for weighing considerable weights. The platinum wire should be 

 replaced by iron wires of larger diameter, firmly stretched, and the level 

 should be made of a piece of very resisting wood. One can also, by 

 adaptation, find the exact value of the most trifling weights. By lengthening 

 a very fine platinum wire several yards, and adapting a long, slender lever, 

 it will not be impossible to ascertain the tenth of a milligram. In this latter 

 case the balance can be set when it is wanted. 



Fig. 20 represents Nicholson's Areometer, which any one may con- 

 struct for himself, and which, as it is here 

 represented, constitutes another kind of 

 balance. A glass balloon, filled with air, 

 is hermetically closed with a cork, through 

 which is passed a cylinder of wood, sur- 

 mounted by a wooden disc, D. The 

 apparatus is terminated at its lower end 

 by a small tray, c, on which one can put 

 pieces of lead in variable quantities. It 

 is then plunged into a glass filled with 

 water. The pieces of lead on the tray, 

 C, are added by degrees, until the stem of 

 the areometer rises almost entirely above 

 the level of the water ; it is next passed 

 through a ring, which keeps it in position, 

 and which is fastened to the upper part 

 of the glass by means of four iron wires in 

 the shape of a cross. The stem is divided 

 in such a way that the space comprised 

 in each division represents the volume of 

 a cubic centimetre. Thus arranged, the 

 apparatus constitutes a balance. The 

 object to be weighed is placed on the disc, D, and the areometer sinks in 

 the water, oscillates, and then remains in equilibrium. If the stem sinks five 

 divisions, it is evident that the weight of the object corresponds to that of 

 five cubic centimetres of displaced water, or five grams. 



It is obvious, therefore, from the preceding examples, that it is not 

 impossible to construct a weighing apparatus with ordinary and very inex- 

 pensive objects. We can, in the same way, show that it is possible to 

 perform instructive experiments with no appliances at all, or, at any rate, 

 with common things, such as everyone has at hand. The lamented Balard, 

 whose loss science has had recently to deplore, excelled in chemical experi- 

 ments without a laboratory; fragments of broken glass or earthenware 



*>- Nicholson's Areometer, contrived to serve 

 as a balance. 



