is yet only in its infancy--that plates of a more delicate nature than those hitherto used, may yet be prepared, and that other properties of light may yet be discovered, which shall facilitate such designs. For, we ought now to set no boundaries to the discoveries of science, and to the practical applications of scientific discovery which genius and art may accomplish. In short, this invention leads to the conclusion, that we have not yet discovered all the wonderful properties of that Luminous Agent which pervades the universe, and which unveils to us its beauties and sublimities--and that thousands of admirable objects and agencies may yet be disclosed to our view through the medium of light, as philosophical investigators advance in their researches and discoveries. In the present instance, as well as in many others, it evidently appears, that the Creator intends, in the course of his providence, by means of scientific researches, gradually to open to the view of the inhabitants of our world the wonders, the beauties and the sublimities of his vast creation, to manifest his infinite wisdom, and his superabundant goodness, and to raise our souls to the contemplation and the love of Him who is the original source of all that is glorious and beneficent in the scene of nature. CHAPTER III. ON THE OPTICAL ANGLE, AND THE APPARENT MAGNITUDE OF OBJECTS. In order to understand the principle on which telescopes represent distant objects as magnified, it may be expedient to explain what is meant by the angle of vision, and the apparent magnitudes under which different objects appear, and the same object, when placed at different distances. [Illustration: _figure 40_*.] The optical angle is the angle contained under two right lines drawn from the extreme points of an object to the eye. Thus AEB or CED (fig. 40.) is the optical or visual angle, or the angle under which the object AB or CD, appears to the eye at E. These two objects, being at different distances, are seen under the same angle, although CD is evidently larger than AB. On the retina of the eye, their images are exactly of the same size, and so is the still larger object FG. [Illustration: _figure 41._]