USE OF THE GONIOMETER. 



713 



USE OF THE GONIOMETER. 



Bring the object into focus near the centre of the field of the 

 micrometer, apply your finger to the knob K, and revolve the 

 micrometer, till the lines of its graduation are parallel to one 



FIG. 434. 



side of the angle to be measured. Revolve then separately the 

 graduated circle, till zero is brought to agree with the point of the 

 index C. Then revolve again the micrometer by the knob K, 

 until the graduation lines are parallel to the other side of the 

 angle to be measured, when the index C will show the value of 

 this angle. (The references are the same in both cuts.) 



The graduated lines of the micrometer are generally ^Jo of the 

 American inch apart. But their relative value as micrometer, 

 with the different object-glasses and eye-pieces, must be ascer- 

 tained by a glass stage-micrometer, and recorded in a table. 



