CHRISTIAAN HUYGENS

in this way. First, it is enclosed in a ring or hollow cylinder made of sheet iron, four digits original: "digitos" — a unit of measurement roughly equivalent to a finger's breadth in length. To this cylinder, or rather to another into which this one is inserted, a one-foot rod the thickness of a finger is attached externally, extending entirely to one side. All these parts rest upon a small brass sphere, the size of a hazelnut, which is connected to the rod and turns quite freely within a hollow of its own size provided below; yet it is secured so that it cannot fall out. The hollow consists of two parts, which are joined and tightened by a screw upon a slender stem, but in such a way that they do not press upon the sphere at all. Thus, the lens, with its attached rod, is made mobile in this manner. Furthermore, so that it may remain evenly balanced, a weight of about one pound is appended below the rod, connected and fixed by a thicker bronze wire half a foot long. By bending this wire, the weight is easily adjusted so that the common center of its gravity and that of the lens coincides with the center of the small sphere. By this means, the lens remains suspended in any position and can be moved with the lightest touch. In this lies the most important part of the invention. For when the stem of the sphere is inserted into the hole of the transverse arm which we described above (two or more such holes are made so that the lens can be conveniently turned toward any part of the sky), a thread or very thin cord is tied to the rod, or its extreme tail; it is intended to connect the larger lens with the one placed closest to the eye, thus matching the length of the future telescope, or rather slightly exceeding it. Hence, when the lens has been raised to the mast, wherever that thread is lightly pulled by hand, it will move the lens along with it, and in this way, guide and oppose it to any star. This certainly could not be done without this balance. Furthermore, in order that the tail or rod, which we have placed on the lens, becomes parallel to the extended thread—which is absolutely necessary—a bronze stylus the length of a finger is fixed to its extreme part. When this is bent downward until its point descends as far below the rod as the center of the sphere, the thread we mentioned is finally attached to it. Why we use a flexible stylus here will be explained later.

Now, it is also necessary to explain the eyepiece lens and how it is composed with the former; this does not require many words, since almost everything that is to be observed for the larger lens is the same. For similarly...