90 



Eyepiece, Diagonal. (i) An eyepiece fitted with a prism to 

 enable the observer to view, at right angles to the axis of 

 the optical instrument, the object. (2) An eyepiece in 

 which a very small portion of the sun's light is reflected 

 from the first surface of a wedge-shaped prism, the rest 

 being transmitted. [2, 3, 6, 9, 10, 11, 13, 15, 17, 18, 20, 21, 

 24, 25, 26, 27.] 



Eyepiece, Ehrlich. A microscope eyepiece with a variable 

 diaphragm, for estimating the number of red and white 

 corpuscles in the blood. [2, 3, 22, 26.] 



Eyepiece, Erecting. The form of eyepiece used in telescopes 

 and microscopes for giving an upright image of the object 

 observed. [7, 2, 3, 8, 9, 10, 11, 13, 15, 16, 17, 18. 21, 22, 23, 

 24, 27.] 



Eyepiece, Huyghenian. A negative eyepiece, designed by 

 Huyghens, for a microscope or telescope. It consists of two 

 plano-convex lenses separated by a considerable space, 

 with both curves turned away from the eye and towards 

 the incidental light. The focal lengths of the field and eye 

 lenses are in the ratio 3:1, while the distance between 

 them is numerically equal to twice the focal length of the 

 eyelens. [2, 3, 17, 18, 20, 21, 22, 23, 26, 27.] 



Eyepiece Indicator. A pointer mounted in a microscope eye- 

 piece. [2, 3, 20, 22, 26] 



Eyepiece, Kellner. An eyepiece giving a very wide field of view. 

 It consists of a cemented pair of achromatic lenses and a 

 double convex lens. The field and eye lenses are of equal 

 focal lengths, and are separated by a distance numerically 

 equal to the focal length of either. [2, 3, 10, 20, 22, .23, 

 26, 27] 



Eyepiece Lenses. Simple or compound lenses used at the eye 

 end of telescopes, etc. [1, 2, 3, 6, 8, 9, 10, 11, 12, 14, 15, 

 17, 18, 20, 21, 22, 23, 24, 25, 26, 27] 



Eyepiece Micrometer. A graduated scale usually placed in the 

 focus of the eyelens of an eyepiece. The graduated scale is 

 often replaced by one or more cobwebs or lines moved by a 

 micrometer screw. [2, 3, 10, 11, 14, 18, 19, 20, 21, 22, 25, 

 26, 27] 



Eyepiece, Monocentric. A concentric eyepiece. [2, 3] 



Eyepiece, Negative. An eyepiece incapable of giving a positive 

 image, i.e., the image due to the objective is formed on the 

 negative side of the field lens. [1, 2, 3, 8, 10, 11, 17, 20, 21, 

 23, 25, 26, 27] 



Eyepiece, Pancratic. An erecting eyepiece of which the power 

 can be varied by altering the position of the lenses. 



Eyepiece, Positive. An eyepiece giving a positive image. 



Eyepiece, Ramsden. A positive eyepiece, designed by Ramsden, 

 consisting of two plano-convex lenses of the same kind of 

 glass, but with their curved faces turned towards each other. 

 The two lenses are of equal focal lengths and separated by 



