98 



WELLS'S NATUKAL PHILOSOPHY. 



Fig. G8. surface of hardened steel, oi 



agate, in order that the beam 

 may turn easily. The scale- 

 pans are suspended by chains 

 from points precisely at equal 

 distances from the fulcrum, 

 and being themselves adjusted 

 so as to have precisely equal 

 ■weights, the two sides will perfectly balance when the pans are empty. 



211. If the two arms of a scale-beam be not of perfectly 

 equal length, a smaller weight at the end of the larger arm 

 will balance a greater weight at the end of the shorter. An 

 excess of half an inch in the length of the arm of the beam, 

 to which merchandise is attached, where the arm should be 

 eight inches long, would cheat the buyer exactly one ounce in every pound. 

 This fraud, if suspected, might be detected instantly, by transposing the 

 weight and the article balanced ; the lightest would then be at the end of 

 the short arm, and would appear lighter than it actually is. 



Fig. 69. 



Under what 

 circumstances 

 ■will a balance 

 indicate false 

 weights ? 



What is the 212. Platform scales, and scales intended 

 construcu™^ for wciglilng hay, etc., are usually compound 

 scales? levers, and are constructed in very various 



forms, but all depend on tlie principles above explained. 

 I'ig. 69 represents one of the varieties, and Fig. 70 a sec- 



FiG. 70. 



