84 naturalists' ASSISTA^fT. 



joints of the apparatus enable a person to raise and depress 

 the lens and still keep it horizontal. The end portion con- 

 sists of a piece of brass tube with a slot cut in it to receive 

 the cover of the lens. Such an instrument can be made for 

 two dollars at the most, and to all intents and purposes will 

 serve instead of a dissecting microscope, all forms of which are 

 more or less inconvenient. When it is desirable to use trans- 

 mitted light, the watch glass or other transparent dish may be 

 placed in the mouth of a bottle and thus sufficient light for 

 all ordinary purposes can be obtained. 



Dissecting microscopes are advertised by all dealers in 

 microscopic goods, but they are but little used by professional 

 naturalists, a triplet with a stand answering all their purposes 

 and that with few of the many objections which they all 

 have. 



The compound microscope is next to be considered. In 

 this instrument an inverted image is formed by the lens 

 (or combination of lenses) nearest the object (called the 

 object glass) and viewed by the other lens nearer the eye 

 (the eye-piece or ocular). These lenses are mounted in a 

 tube fitted with appliances for bringing them nearer to or re- 

 moving them farther from an object placed on the stage. 

 Suitable methods are also employed for illuminating the ob- 

 ject, and a stand to support the whole completes the list of 

 necessary portions. These will now be taken up in order and 

 their various requisites discussed. In this the writer is well 

 aware that the views advanced are in direct opposition to 

 those held by many microscopists, but he is also aware that 

 they are in almost full accord with the opinions of those who 



