( «97 f

From that time I was intemipted till this last: Autumn, when I made ano-ther. And as that was sensibly better than the Erst, (especially for Day Ob-jects) lb I doubt not, but they will he still brought to a much greatef Pcr-fection by their Endeavours, vvho, as you insorm me, arc taking care aboutit at London.

2.. This new Instrument is composod of two Metallinc Speculums, the.^ «<■» cauii-one Concave, (instead of an Object Glals) the other Plain : and also of a ^vcntJfh^^1 drall Piano-convex Eye Glast ; as in the Figurc, where AB is a Concave ur. Newton.Speculum, of. which the Radius or Semidiametcr is ixf or i z Inches. n. 8i> p. 4004.

CD, anothcr Metallinc Speculum, whose Surface is Flar, and the Cir-cumfercnce Oval.

G D, an Iron VVire, holding a Ring of Brast, in which the Speculum C Dis fixed.

F, a sinall Eye Glast, Fiat above, and Convex below, of the ixtli partof an Inch Radius, it not lest.

GG G, the forc part of the Tube (which is opcn) fastncd to a Brast Ring.

HI, to keep it immoveablc.

P Q_K L; the hind part of the Tube, fastncd to anothcr Braß Rin;' ;

pa

O, an Iron-Hook fastncd to the Ring P Qj> and furnisht with a Skrew N*ithereby to advance or draw back the hind part ot the Tübe, and so by thatmeans to put the Specula in their due distancc.

M QGI, a crooked Iron stistaining the Tube, and fastncd by the Nais'

R to the Ball and Socket S, wherehy the Tube may be turncd every way.

The Center of the Flat Speculum C D, must be placed in the kirne Pointsof the Tube’s Axe, where falls the Perpendicular to this Axe, drawn to thefame from, the Center of the little Eye Glast, which Point is here ■ markeAat T.

And to give the Reader some Satisfiction to understand, in what Dcgrce itreprefents tnmgs distinet, and free from Colours, and to know the Aperture,by which it adraits Light, he may compare the Distanccs of the Focus Efrom the Vertexes of the little Eye Glast and the Concave Speculum; that is,-EF, t of an Inch, and ET V, 6y Inches, and the Ratio will be found as1 to 38; whereby it appears, that the Objects will be magnified about z 8times, and.be reprelented bigger by xi times in Diameter, when lecn throughthis, than through an ordinary Telelcope of about two Foot long.

Thus far as to the Structure of this Telesoope. Concerning the mcrallinc.

Matter, fit for these Refleaing Speculums, the Inventor bath also cohfideredthe ßme, and gives this Caution, That whilst Men stek for a YVhite, Hard,and Durable Metallinc Compositiön, they resolve not upon flieh, an one, as.is füll of Imall Pöres, only disooverable by a Microlcope. For though such.an one may to appearance take a good Polisti, yet the Edges of thole ImallPores will wear away faster in the Polilhing than the other Parts of the Me-.tal; and so, however the-Metal leern Polite, yet it (hall not Reflect with.such an accurate-regularity as it ought to do. Thus T in-Glast mixt with -ordinary Bdl-Metal makes it morc White, and apt to Reflect a greater quan-

tity