File:Hardwicke's science-gossip - an illustrated medium of interchange and gossip for students and lovers of nature (1886) (14769447745).jpg

Identifier: hardwickesscienc22cook (find matches)
Title: Hardwicke's science-gossip : an illustrated medium of interchange and gossip for students and lovers of nature
Year: 1886 (1880s)
Authors: Cooke, M. C. (Mordecai Cubitt), b. 1825 Taylor, J. E. (John Ellor), 1837-1895
Subjects: Science Natural history
Publisher: London : Robert Hardwicke
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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mirror cannot be employed. It is, however,desirable always to have the point D accurately in theaxis of the microscope, unless a pencil of oblique raysis intentionally to be employed. In passing, I mayremark that an object on the stage, when under 250 HARD WICKES SCIENCE- G OS SIP. observation, must, of course, be in the axis of theinstrument, otherwise the eye could not see it.When, therefore, we bring rays to a focus on theobject, that focus will be in the said axis also. In Fig. 158 rays of light, L L L, which are parallelboth to c D, the principal axis, and to each other, fallupon the mirror, and are reflected to a point F, in the If the microscopist could make use of the principalfocus, it would often be advantageous to do so,because the rays are so symmetrically reflected, andso nearly brought to an exact focus ; but he cannot.The object on the stage would need to coincide inposition with the point F, or nearly so. The surfaceof the mirror would therefore be upwards towards the
Text Appearing After Image:
M .-.<■■:- Fig. 159.

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