Optics.

that the Line of XII be exactly in the Meridian)that the Position of R in the Fork be such that 0 [Sun’s Rays go directly through it, and the Shadesthe Style’s Top fall just upon the Hole; moreover if,Distance of the Centre of the Speculum S from the * „of the Style/be made equal (by the Pof.tor) t0Distance of the central Point of R therefrom ; and M jfthe Tail of the Speculum DE passing through P-Mthen the Clock be put into Motion, the Index }shall carry about the Tail of the Speculum in fue .Manner, that at all Times of that Day when the J 5 .can come upon the Speculum it will reflect the Fhconstantly in one and the fame Position and Dirt’^all the time without Variation. . j

30. The Machine thus constituted is placed ^Box or Cafe, and set in a Window with one Side op^exposed to the Sun, and all the other Parts close Lj,that when the Room is made dark, and the Solas ^crofcope fixed to the Forepart of the Box in which ^Heliojiata is placed, just against the Centre of theculum to receive the reflected horizontal Beam, all ( <|

Experiments of the darken’d Room are then perso^ j

- ■ — - • * ■ ^ o>

as usual. This is a very ingenious Construction

Sohtr-Microscope Apparatus^ and full of Art, but, 1too expensive and troublesome for common Use.ever, ’tis easy to fee that this Machine is capab^ jbeing greatly reduced j for it may be made to an^the End very well without a Clock ; also the Spec u ‘^may be Glass instead of Metal, and all fix’d ohFoot or Pedestal: But this I Rave to the Ingenuitythe Mechanical Reader.