C 8 )

of by such whose sight is weak , but such as can endure itsomewhat brighter, and would fee the parrs more strong, maymake use of one of three Reflections only, like that of Fig. 14.which doth best suit my eye.

Next, this Helioscope may be made by Reflection only, with-out any Refraction, and that may be done either in the man-ner of that in the seventh Figure, when<*£represents a con-cave surface of a black Glass, whose focus is 0, which, for In-stance, we will suppose at the distance of forty foot, cd repre-sents a clear plate of Glass of two flat surfaces,which are madenot parallel but a little inclining, so as the reflection from thatside which is furthest from the concave may be cast anotherway,and not fall at all upon the third Reflecting-plate * £, andbecause the wedg like form of this transparent plate of Glass,cd , will cause a refraction, and consequently a coloration ofthe Ray ; therefore there must be another wedg-like Plateexactly as may be like the former, which at some distance, asat mp, where the reflection will not come to fall upon thePlate, * £ must be so fixed that the thinnest part of this maylie just upon the thickest part of cd, and the thickest of thisover the thinnest of that, by which means both the false refle-ctions and refractions will be removed. From e £ the Rays arereflected to y S, and from y ® to 0 the focus, and so through thelens,«, to the eye*. This I take to be the best by Reflection ;bur it may be twenty other waies contrived , which I lhallnot now spend more time in describing, it being so easie a mat-ter from the consideration of these I have mentioned, to makean hundred other variations of the principle.

To this Helioscope may be fitted Instruments for measuringthe Macula , facttlœ , and Nebula , visible in the body ofthe Sun, as also the spaces passed by them in a day, two, three,ten, &c. together with the variation of their Figures and Mag-nitudess but the diameter of the body of the Sun will be bet-ter taken by the following Instrument. And by reason that it.will be often necessary to draw their figures more exactly, theEngine that I have described in my Animadversions , in the67, 6 S, and 69 pages>nray be made use of to keep the Helioscopeal waies directed at the body of the Sun, which will be no smallease to an Observer, that is to delineate the figures on Paper.

When