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projects an arm two inches long to the end of which the spring is at- 

 tached. From the lower end of the spring is suspended an indicator of 

 the form shown in figure I. with the usual pans below. The shelf shown 

 in figure I upon which the point of the indicator rests when not in use 

 is made of sheet brass and is fastened to the column one foot from the 

 lower end. Tacked to one of the side sti'ips immediately below this shelf 

 so that it projects over the meter sticlv slightly is a small metal plate 



Pointer 



Sprinci 



bearing a horizontal scratch. The distance from the top of the meter 

 stick to this scratch can be read with considerable accuracy to the tenth 

 part of a millimeter. Below this shelf slides a table upon which vessels 

 of water, etc., can be placed. To use the apparatus the spring must first 

 be calibrated. Incidentally, Hooke's law may be verified. To do this a 

 reading of the distance from the top of the stick to the scratch is taken 

 when the spring is so adjusted that the pointer barely swings clear of 

 the shelf, no load being in the pans. A load of one gram is then added 

 and the spring is stretched,— by raising tlie meter stick with the before 

 mentioned cord and screw— until the pointer clears the platform again. 

 The distance from the top of the meter stick to the scratch is again read. 

 The difference between the two readings gives the elongation for a load 

 of one gram. For ordin.Mry work rliis eloiigiition should be al)out five 



