THE KYKriKCE 153 



2. Use eoniponsatins (or phiiw) eyepieces witli acliroiuaiic 

 objectives of apertures of 0.85 and over. 



3. Employ compensating eyepieces of the same make as the 

 apochromatic objectives used with them. 



4. Get all eyepieces parfocal. 



5. Use specially corrected eyepieces for photography, either 

 the projection oculars, or the homals. 



6. For flatness of field, special photographic eyepieces have 

 been designed (homals). 



7. Change objectives rather than eyepieces, as a rule. 



8. Use the new method of designating eyepieces and objec- 

 tives by their magnifications. 



9. For long-continued work it is best to have the measuring 

 eyepiece provided with a screw to move the scale. 



10. Accurate measurements can be made by photographing, at 

 once or successively, both object and scale. 



