Identifier: younggentlemanla02mart (find matches)
Title: The young gentleman and lady's philosophy : in a continued survey of the works of nature and art by way of dialogue
Year: 1759 (1750s)
Authors: Martin, Benjamin, 1704-1782
Subjects: Science
Publisher: London : Printed and sold by W. Owen and by the author
Contributing Library: University of Pittsburgh Library System
Digitizing Sponsor: University of Pittsburgh Library System

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s moft delightful, indeed, as for Inllance, fuppofe it was 3 or 4 Feet focal Diilai-ice, the Image of the Suns Image mightbe thereby eafily made 5 or 6 Inches in Diameter, which will be large enough for all the before-mentiontd Purpofes. But to return \ this fecond Image is that which we view by theEye-glafs of the Telefcope, in the fame Manner as the large Imageis viewed by the Eye-glafs in the upper Part of the compound Microfcope : From all which it appears, that a refleiling Telefcope is a compound Inftrument, confijVmg of a Telescopeand a Microscope ; and if the Metals are fuch as are before-niention, whofe focal Diftance are as 9 to i, then, as a Tele-fcope, it will magnify 9 Times, and in the Microfcope Part itwill magnify 10 Times j therefore, upon the Whole, it willmagnify 9 Times 10, or 90 Times, and all this in aLengthofTube not greater than 14 Inches. Euphrof. By this compound Power of magnifying I readilydifcern the Reafon, why a reflcding Telefcope is fo very fhort. com-
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and Lady*s Philosophy. 2±i tompared with a Refraaor of the fame Power, and confequent-\y how much more convenient they are for Ufe^ as they areeafily applied to a proper Stand or Pedeftal, and are capable ofa Motion every Way, which not only facilitates its Ufe, but renders it vaftly more pleafant and agreeable. - But one Thing I muft remind you of, Ckonicus; I remember, fomeTime ago, I afked you what was the magnifying Power of thisTelefcope, and 1 remember you told me, it was about 5bTimes, or fomewhat more : How, then, does that agree withthe magnifying Power you now mention of 90 Times ? Clean, I will foon fatisfy you in that Particular. I have atprefent fuppofed, for your more eafy Comprehenfion, that thefocal Diftance of the fmall Speculum is only one Inch ; but thatis found, by Experience, to be too imall, or the Power of ma?-hifying too great, to admit of a fufficient Degree of Diftindnefsand Brightnefs in viewing common Objeclsi and therefore it isCuftomary now to make the f

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