It must be remembered that these eyepieces give an inverted image—or rather the object glass gives an inverted image, and the eyepiece does not right it again; but there are eyepieces that will erect the image, and Rheita’s is one of this kind. It is, as will be seen from Fig. 63, merely a second application of the same means that first inverts the object, namely, a second small telescope. A is the object-glass, _a b_ the image inverted in the usual way; B is an ordinary convex lens sending the rays from _a_ and _b_ parallel. Now, instead of placing the eye at C, as in the ordinary manner, another small lens, acting as an object-glass, is placed in the path of the rays, bringing them to a focus at _a´_, _b´_, and forming there an erect image which is viewed by the eye-lens D. This is the erecting eyepiece or “day eyepiece,” of the common “terrestrial telescope.” Dollond substituted an Huyghenian eyepiece for the eye-lens D, and so made what is called his four-glass eyepiece. Dr. Kitchener devised and Mr. G. Dollond made an alteration in this eyepiece in order to vary its power at pleasure. It is done in this way: The size of the image _a´ b´_ depends upon the relation of the distances _a_ B and E _a´_, which can be varied by altering the distance of the combination of the lenses B and E, from the image _a b_, and so making _a´ b´_ larger and at a focus further from E; the tube carrying _d_ slides in and out, so that it can be focussed on _a´ b´_ at whatever distance from E it may be. This arrangement is called Dollond’s Pancratic eyepiece. [Illustration: FIG. 63.—Erecting or day eyepiece. ]