made achromatic. As the regular eyepiece of two 

 systems reverses the image, the erecting eyepiece again 

 reverses it, thus bringing the image back to the original 

 position* of the object. It is seldom used with the 

 microscope, but is necessary with small hand telescopes 

 and in the telescopes of surveying instruments. 



Index Eyepiece is one which is provided with 

 an index or pointer to indicate a particular object in the 

 field or a certain structure of an object and is especially 

 valuable in class demonstration. The index can be 

 swung in and out of the field at will. Any of the 

 Huyghenian eyepieces may be converted into an index 

 eyepiece by cementing with shellac or Canada balsam an 

 eye-lash or sharp black paper wedge to the diaphragm 

 with the point toward the center of the field. 



Compensating Eyepiece. In this place it is 

 also proper to speak of the new compensating eyepiece 

 as made by Prof. Abbe. This eyepiece compensates 

 for the residual errors in the apochromatic objectives 

 and is of no value except when used with them as 

 it is highly over-corrected, as can be seen at the edge 

 of the field, which has a strong orange color, whereas 

 in the Huyghenian it has a blue color. 



In this series of eyepieces there is a searcher which 

 is of low power and intended to find objects. The 

 higher powers are for general work, some of them 



in 



