A Description of Helioscopes, and Some Other Instruments

is lost with every reflection, and that every reflection doubles, triples, quadruples, quintuples, etc., the initial ratio of loss. For instance:

Suppose I have a Helioscope An early instrument designed by Hooke for observing the sun without blinding the viewer. made of an Objective Lens original: "Object Glass", an Eyepiece original: "Eye Glass", and four Reflecting Mirrors original: "Reflecting Glasses", and that, by the first reflection, I lose 3/4 of the Direct light. I assert there will remain but 1/256 part of the Direct rays of the Sun which can finally reach the eye. For if every reflection loses 3/4 of its rays and reflects only 1/4, and that quarter then loses 3/4 and reflects only 1/4 of the light it received, there will remain but 1/16 part of the whole. And if this sixteenth part loses three-quarters of its rays and reflects only a fourth, it follows that the remainder will be only 1/64 part of the whole. Finally, if that is reflected once more, the ray will return with only 1/256 part of its original light.

This, although it is obvious and easy enough to understand now that it is known, I have not yet found any person who has thought of applying it to this use. The majority of observers have until now used either very opaque and thick glasses next to the eye—whether of red, green, blue, or purple glass; others have diminished the glare original: "Radiation" by covering the glasses with a very thick and dense coat of soot from a lamp; others by projecting the image onto a piece of white paper, from which it is reflected to the eye; others have narrowed the aperture The opening through which light enters. into a smaller circle, thereby letting in less light and using a single ray instead of a beam original: "pencil" of rays; others have expanded the image of the sun, with the help of eyepieces, into a circle ten, twenty, or a hundred times its diameter. But none of these ways come close to the method I now describe using three, four, or more reflections, as anyone will very clearly discover upon trial.

First, as to the colored glasses, I cannot approve of them at all because they tint the rays with that same color and consequently ruin the accuracy of the appearance regarding color; besides, it imposes a haziness and dimness upon the figure so that it does not appear sharp and distinct. The same inconvenience is also produced by Mr. Huygens's original: "Monsieur Hugenius," referring to the Dutch scientist Christiaan Huygens. method of covering the glass with the soot of a