Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses. With observations and inquiries thereupon / By R. Hooke.
- Robert Hooke
- Date:
- 1665
Licence: Public Domain Mark
Credit: Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses. With observations and inquiries thereupon / By R. Hooke. Source: Wellcome Collection.
36/384
![The pREFAC E. mrnfhe longer the Glafl be, the bigger aperture will it bear,if the Glaffes be of an equal gocdnefl in their kind. Therefore, a fix will indure a much larger Aperture then a three foot Glafl; and a fixty foot Glafl will proportionably bear a greater Aperture then a thirty,and will a* much ex¬ cel it alfo at a fix foot does a three foot, as I have experimentally obfervd in one of that length made by Mr. Richard Reives here at London, which will bear an Aperture above three inches over, and yet make the Objett proportionably big and difintt; whereas there are very few thirty foot Glaffes that will indure an Aperture of more then two in¬ ches over. So that for Telefcopes, fuppofng we had a very ready way of making their Object Glajfesof exaftly fpherical Surfaces, we might, by increafng the length of the Glafl, magnifie the Object to any affignable big- nefl. And for performing both thefe, I cannot imagine any way more ea- fie,andmore exalt, then by this following Engine,by means of which, any Glaffes,of what length foever,maybe ffeedily made.lt feems the moft eafie, becaufe with one and the fame Tool may be with care ground an Objebi Glafl, of any length or breadth requifite, and that with very little or no trouble in fitting the Engine, and without much skill in the Grinder. It feems to be the mofl exalt, for to the very lafl flroke the Glafl does regulate and rettifie the Tool toitsexatt Figure; and the longer or more the Tool and Glafl are wrought together, the more exali will both of them be of the defir d Figure. Further, the motions of the Glafl and Tool do fo crofl each other, that there vs not one point of eithers Surface,but has thousands of crofl motions thwarting it, fo that there can be no kind of Rings or Gutters made either in the Tool or Glafl. r’t t:' > v.nou The contrivance of the Engine isj only to make the ends of two large Mandrils fo to move , that the Centers of them may be at any convenient* difiance afonder , and that the Axis of the Mandrils]ying both in the fame plain produc’d, may meet each other in any affignable Angle } both which requires may be very well perform’d by the Engine deferib’d in the third Figure of the firft Scheme : where A B fignifies the Beam of a Lath fixt per¬ pendicularly or Horizontally, C D the two Poppet heads, fixt at about two foot difiance, E F an Iron Mandril,whofe tapering neck F runs in an adapt¬ ed tapering brafs Collar^ the other end E runs on the point of a Screw G 5 in a convenient place of this is faflned H a pull y Wheel, and into the end of it,that comes through the Poppet head C, is forewed a Ring of a hollow Cylinder K, or fome other conveniently fhap’d Tool, of what widenefs fhall ■' be](https://iiif.wellcomecollection.org/image/b30326370_0036.jp2/full/800%2C/0/default.jpg)
