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The proper combination of apochromatic objec- 

 tive and compensating eyepiece gives a beautiful 

 image with the maximum of resolving power, 

 unapproached by any of the achromatic combina- 

 tions. They furthermore have the advantage that 

 they are exactly suited to photomicrography, 

 there being exact coincidence between the photo- 

 graphic and visual image, which in the achromatic 

 objectives is not the case, as these must be either 

 corrected for photography, when they are not sat- 

 isfactory for ordinary purposes, or an allowance 

 must be made for the difference between two 

 images in the camera, which is very difficult. 



One objection to the high powers has been the 

 liability of deterioration in some of the materials 

 used, which has happily been overcome by Prof. 

 C. S. Hastings of New Haven, Conn., in the 

 apochromatic objectives, which have been com- 

 puted by him for the Bausch & Lomb Optical Co. 



Eyepiece or Ocular.- -The purpose of the eye- 

 piece is so to refract the diverging rays coming 

 from the objective that they will reach the pupil 

 of the eye and while the most simple part of the 

 optical combination is, withall, an important part of 

 it. In fact it may be said that, owing probably to 

 its simplicity, it has been neglected and very often 

 eyepieces are furnished which are not at all com- 

 mensurate with the quality of the objectives. 



