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Huygenian Eye-pieces. 



We supply HUYGENIAN eye-pieces for use with achromatic objectives in 

 five different powers. The various focal lengths of these eye-pieces are serially 

 graduated so that, with due regard to their peculiar variations in the position of 

 their lower focal points, the magnifications X 3, 4, 5.5, 7 and 9 are obtained if 

 the tube-length of 160 mm be maintained throughout. 



We make also a Huygenian ocular 2* with iris-diaphragm similar to the 

 compensating ocular 4*. 



What has been said with regard to compensating eye -piece 4* applies 

 equally to this HUYGENIAN eye-piece 2*. (Sec p. 12.) 



Regarding eye-pieces for special purposes (micrometer , spectroscopic , &c.) 

 see under heading of Accessory Apparatus, pp. 92, pj, 106. 



We would particularly emphasize the fact that HUYGENIAN eye-pieces 

 are designed for use with achromatic objectives only. 



List of Huygenian Eye-pieces. 



In subsequent orders for eye-piece 2* the factory number of 

 the stand should be noted. 



We supply in addition two forms of the Ramsden eye-piece, one of them in 

 combination with our screw micrometer eye-piece (see p. 93), the other, which 

 is termed Orthomorphic eye -piece 4 (see p. 72), for use with binocular micro- 

 scopes. 



, Sena, 



