Encyclopaedia; or, A dictionary of arts, sciences, and miscellaneous literature; constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises of . rt of the image which corre-fponds to the middle of the objeft muft appear to theobierver more dark and confufed than the extremeparts of it. Befides, the fpecidum EF will alfo inter-cept many rays proceeding from the objeft; and there-fore, unlefs the aperture TT be large, the objeift muftappear in fome degree obfcure. In the bcft refledling telefcopes, die focus of thefmall mirror is ne
Encyclopaedia; or, A dictionary of arts, sciences, and miscellaneous literature; constructed on a plan, by which the different sciences and arts are digested into the form of distinct treatises of . rt of the image which corre-fponds to the middle of the objeft muft appear to theobierver more dark and confufed than the extremeparts of it. Befides, the fpecidum EF will alfo inter-cept many rays proceeding from the objeft; and there-fore, unlefs the aperture TT be large, the objeift muftappear in fome degree obfcure. In the bcft refledling telefcopes, die focus of thefmall mirror is never coincident with the focus of thegreat one, where the firft image KH is formed, but alittle beyond it (with refpeft to the eye), as at n ;the confequence of which is, that the rays of the pen-cils will not be parallel after refleilion from the fmallmirror, but converge fo as to meet in points aboutQ__yQ_j where they would form alarger upright imag^than PV, if the glafs R. was not in their way ; andthis image might be viewed by means ol a fingle eye- ^glafs propeily placed between the image and the eye : jbut then the field of view would be lefs, and confe- quentlj y-/^. /. 0 p r I c s. Plate CrCLXX. ^y^/.-t ,/ -yy^.H. K,. r^ v^___— — ^^—XT I b:
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Keywords: ., bookcentury1700, bookdecade1790, bookidencyclopaedi, bookyear1798
