60 PRACTICAL MICROSCOPY. 



of magnifying power without changing the objective, and 

 this is especially useful in either dissecting or photography 

 by means of the microscope. 



The field of view is also much increased, so that a very 

 large object can be included when using the half-inch objec- 

 tive, and by pulling out the draw-tube (containing the 

 erector, of course) a very considerable increase in amplifi- 

 cation is obtained ; thus, in the author's dissecting micro- 

 scope, when the erector is placed as near to the objective 

 as possible, the magnification obtained scarcely exceeds 

 8 diameters, while when the draw-tube is pulled fully out 

 the amplification is increased to 1 30 diameters. It should 

 be understood that the defining power of a microscope is 

 not increased by the addition of an erector. 



The double nose-piece next claims our attention, and was 

 devised by Mr. Brooke for the purpose of quickly changing 



FIG. 34. FIG. 35. 



the objectives without the trouble of unscrewing and screw- 

 ing up again each time. This accessory is made in several 

 forms, but that shown in Fig. 34 is specially recommended, 

 the straight pattern being sometimes inconvenient, owing to 

 the one objective touching the stage before the other re- 

 quired for use is in focus. It is a very useful addition to the 



