THE MICROSCOPE AND ITS PARTS. 5 



The reader perceives that this matter of short focus 

 is an important one ; indeed the usefulness of the pock- 

 et-lens to a great extent depends upon it. Reject with- 

 out hesitation the simple lens whose focus is so short 

 that it must be held almost in contact with the object. 



Not long ago a rather expensive instrument called the 

 " Craig Microscope" was extensively advertised, and sold 

 as a remarkable thing. The lens was a small globule of 

 glass fastened to a glass plate, to give it a flat under-sur- 

 face, and mounted in a brass ring, the whole being sup- 

 ported on an upright brass tube with a plane mirror at 

 the lower end. It was not a compound microscope, but 

 a simple lens with mirror attachment. The object to 

 be examined was suspended from the flat surface of the 

 glass in a drop of water, the focus being so short that 

 it was at the front of the lens, so that nothing could 

 be looked at unless it was adherent to the glass. No 

 mounted object could be satisfactorily studied ; to ex- 

 amine the parts of a flower was impossible, and even 

 when a drop of water was suspended from the lens its 

 contents were distorted almost beyond recognition. 



The " Excelsior Microscope " makes no false pretences. 

 The instrument consists of a small box which is a recep- 

 tacle for all the parts when not in use, and a support 

 when the steel rod is elevated to receive the combina- 

 tion pocket-lens and the stage, on which the object is to 

 be placed, a small mirror in the front of the box re- 

 flecting the light to the object from below. A great 

 fault is the absence of weight in the instrument. At 



