LECTURE AND LABORATORY PRACTICE. 



171 



IV. — A Cheap Demonstration Balance. 



This balance, Fig. 4, is an ordinary balance made to take a load 

 of 1,000 grams (catalogue price £2 18s. 6d.) fitted with a light 

 aluminium pointer A about 21 in. long playing over a cardboard 

 scale B. The scale and pointer are turned towards the class, the 

 ordinary scale and pointer being towards the lecturer. The pointer 

 can be made of any length suitable to the distance between the 

 lecturer and the class, and is counterbalanced by a binding screw C 

 clamped on the ordinary index. The cardboard scale is made so that 

 the readings of the pointer on the scale coincide with those of the 

 ordinary index and scale. One arm of the balance is graduated for 

 use with a '1 gram rider. 



Fh. i. 



The balance is provi'ded with a glass case, the aluminium 

 pointer and support for the scale passing through the roof. The 

 balance has proved very useful in demonstrating, to large classes, the 

 method of determining small weights by vibrations, as well as for 

 general lecture experiments. The pointer and scale in no way inter- 

 fere with its use for ordinary purposea 



