A Description of Helioscopes, and Some Other Instruments

Secondly, a way of shortening reflective and refractive telescopes.

Thirdly, a way for using a lens original: "Glaſs" of any length, without moving the tube.

Fourthly, an instrument for measuring original: "taking" the diameters of the sun, moon, and planets, or for measuring any other distances up to five or ten degrees, with the accuracy of a single second. I promised two of these on the 78th (and final) page of my Animadversions Referring to Hooke's 1674 work, Animadversions on the first part of the Machina Coelestis., and the others are included here as they are related to them.

Fifthly, an instrument for drawing original: "deſcribing" all kinds of sundials using tangent projection.

1. For adjusting the hand of a clock so that it moves within the shadow of a sundial whose style The gnomon or blade of a sundial that casts the shadow. is parallel to the Earth's axis.
2. In the azimuth The horizontal angle or direction of a celestial object. of any celestial body—that is, in the shadow of an upright or any other kind of tilted style upon any flat surface.
3. For making a clock hand move according to the true equation of time The difference between time as shown by a sundial (apparent solar time) and time as shown by a clock (mean solar time)..
4. For making all kinds of elliptical sundials, using Mr. Foster's method, etc.
5. For transmitting circular motion along a curved line without any shaking; and for various other excellent purposes.

And first, regarding a HELIOSCOPE, which shall reduce the brightness of the sun so much that even the weakest eye may look upon it at any time without the least discomfort original: "offence". My invention original: "contrivance" works by repeatedly reflecting the rays from the surfaces of black glass plates which are ground very precisely flat and highly polished. This diminishes the radiation so that eventually it becomes as weak and faint as the moonlight at twilight. In this way, one may with ease and great pleasure view, examine, and describe the phase of the sun, as well as its spots original: "maculæ" and bright patches original: "faculæ", should any appear when the observation is made. This provides a good opportunity for discovering them before receiving any notice original: "advertiſement" from others. The reason for this will be clear enough to those who consider how great a quantity of light rays—