26 SCIENTIFIC RECREATIONS. 



the Centre of Gravity, and the Balance, and upon the latter we have a few 

 remarks to make first, for a well-adjusted balance is a most useful thing, 

 and we will show you how to make one, and then proceed to our illustra- 

 tions of the Centre of Gravity, and explain it. 



All those who cultivate experimental science are aware that it is useful 

 to unite with theoretical ideas that manual dexterity which is acquired by 

 the student accustoming himself to practical operations. One cannot too 

 strongly urge both chemists and physicists to exercise themselves in the con- 

 struction of the appliances they require, and also to modify those already 

 existing, which may be adapted to their wants. In a large number of cases 

 it is possible to manufacture, at small expense, delicate instruments, capable 

 of rendering the same service as the most elaborate apparatus. Important 

 scientific labours have often been undertaken by men whose laboratories were 

 most simple, who, by means of skill and perseverance, knew how to do great 

 things with small resources. A delicate balance, for instance, indispensable 



Fig. 19. Torsion balance, which can easily be constructed, capable of weighing a milligram one-tenth of full size 



alike to chemist and physicist, can be manufactured at little cost in different 

 ways. A thin platinum wire and a piece of wood is all that is needed to make 

 a balance capable of weighing a milligram ; and to make a very sensitive 

 hydrostatic balance, little is required besides a glass balloon. Fig. 19 

 represents a small torsion balance of extreme simplicity. A thin platinum 

 wire is stretched horizontally through two staples, from the wooden sup- 

 ports, A B, which are fixed in a deal board. A very thin, delicate lever, C D, 

 cut in wood, or made with a wisp of straw, is fixed in the centre of the 

 platinum wire by means of a small clip, which secures it firmly. This lever is 

 placed in such a manner that it is raised perceptibly out of the horizontal line. 

 At D is fixed a paper scale, on which is put the weight of a centigram. The 

 lever is lowered to a certain point, slightly twisting the platinum wire. Near 

 the end of the lever a piece of wood, F, is fixed, on which is marked the 

 extreme point of its movements. Ten equi-distant divisions are marked 

 between these two points, which represent the distance traversed by the 

 lever under the weight of the milligram. If a smaller weight than a 

 centigram is placed on the paper scale the lever falls, and balances itself 



