Measurement of Weight 49 



for it such that, when the rod is again left free to 

 move, it takes up a horizontal position 1 . 



Tie a fine thread of cotton around a new penny 

 and make a loop in the free end of the thread of suffi- 

 cient size to slide freely along the rod. Hang the penny 

 from the rod at any point on one arm. On the other 

 arm hang another new penny, similarly tied with an 

 equal length of the same sort of thread. Arrange the 

 position of the second penny so that the rod is again 

 horizontal. Measure carefully the distance from the 

 centre of the top edge of the rod above the needle to 

 the point from which each penny is suspended. Note 

 and compare the measurements obtained. (If a metre 

 scale be used the lengths required may be readily 

 read off directly from the graduations of the scale.) 



Move the first penny to a new position on the rod 

 and adjust the position of the second till the rod is 

 once more horizontal. Note and compare the distances 

 from the centre of the rod to the point of suspension 

 of each penny. 



Next hang two pennies, using a double allowance 

 of thread, on the rod in place of the second penny, 

 leaving the first on the other arm. Adjust till hori- 

 zontality is attained and note and compare the distances 

 measured as before. Repeat the above operations, 

 using varying numbers of new pennies on each arm of 

 the rod. 



On carefully comparing the results obtained, it 

 will be at once seen that the further a penny is hung 

 from the point of support at the centre of the rod 

 (usually termed the " fulcrum "\ the greater is its 



1 Greater delicacy of adjustment may be attained if two thin glass 

 plates be interposed between the ends of the needle and the upper faces 

 of the blocks. 



H. D. s. 4 



