30 HOW TO USE THE MICROSCOPE 



thin cover-glass, or otherwise held in position, is 

 placed on the stage (7) and secured in the field of 

 vision by the stage springs (8). The instrument is 

 placed in a suitable position in relation to the 

 source of light, and light is reflected through it by the 

 mirror (10). To secure good and even lighting, the 

 sliding mirror fitting (15) may need to be raised or 

 lowered on the tail-piece (14). The mirror has two 

 surfaces, one concave, and the other plane. The 

 concave surface is used with high-power objectives, 

 and the plane with low-power. 



We are now ready for focussing, which must be 

 done with care. Rash and hasty raising and lower- 

 ing of the body tube may lead to disaster to both 

 object and object glass. Let us suppose that we 

 are using a 1-inch objective. Making use of the 

 milled heads (3) controlling the coarse adjustment, 

 we lower the nose of the objective until it is within 

 about I inch of the object. Placing the eye to the 

 ocular, we slowly raise the tube until we see a 

 clearly defined image of the object. Using a 1-inch 

 objective, it is probable that we shall be able to 

 focus sufficiently accurately with the coarse adjust- 

 ment alone, but with higher powers we first roughly 

 focus with the coarse adjustment, and do the final 

 focussing with the fine adjustment (4). Let it be 

 a rule always to raise the tube in the first focussing. 

 If it be lowered towards the object while the eye is 

 at the ocular, the novice will very likely lower too 

 far and break the object, perhaps doing other 

 damage as well. A high-power objective will need, 

 in the first instance, to almost touch the cover-glass, 

 from which position it must be raised very gradually. 



