The early origin of the telescope, like that of most other important inventions, is lost in obscurity, and it is now impossible to determine who was the first maker. It is certain that some time prior to the end of the 13th century lenses were in common use for assisting in procuring distinctness of vision. A certain Vitello, a native of Poland, seems to have done something in this line; and Eoger Bacon, in one of his works, employs expressions which show that even in his time (he died in 1292), spectacles were known.

Seeing that this was the case, it is almost certain that some combination of 2 or more lenses must have been made in the interval which elapsed between Bacon's time and the commencement of the 17th century, when telescopes are usually considered to have been invented. Dr. Dee mentions that though some skill is required to ascertain the strength of an enemy's force, yet that the commander of an army might wonderfully help himself by the aid of “perspective glasses,” a phrase which must refer to some kind of optical instrument then in use

One of the most important total eclipses of the Sun. that has occurred within the last few years was that of July 28, 1851. Though not visible in England, it was seen to great advantage in Sweden, to which country astronomers flocked in great numbers. From the numerous observations that were made, and subsequently published, we select some extracts which will doubtless interest the reader. The following remarks are from the pen of Mr. G. B. Airy, the Astronomer Royal, who observed it at Göttenberg: —

Around the Sun as a centre, certain bodies, called planets, revolve, at greater or less distances: they may be divided into two groups, (i.) The inferior planets, comprising Vulcan, Mercury, and Venus; and (ii.) the superior planets, including Mars, the Minor Planets, Jupiter, Saturn, Uranus and Neptune, the Earth being the boundary between the two. If viewed from the Sun, all the planets, inferior and superior, would appear to spectators placed on the Sun, to revolve round that luminary in the order of the zodiacal signs; such, however, is not the case when the motions of the planets are watched from one of their number itself in motion; it consequently happens that the apparent motions of the inferior planets on the one hand, and the superior on the other, differ considerably. The former are never seen in those parts of the heavens in opposition to the Sun, but are sometimes to the east and sometimes to the west of it. Twice in every revolution an inferior planet is in conjunction with the Sun (Fig. I); in inferior conjunction, when it comes between the Earth and the Sun, and in superior conjunction when the Sun intervenes between the Earth and the planet. When it attains its greatest distance from the Sun, east or west, it is said to be at its greatest elongation—east or west, as the case may be.

Jupiter is the largest planet of the system, and when in and near opposition shines with a brilliancy inferior only to Venus. A friend of the writer has informed him that on October 16, 1857, the planet's lustre was so considerable as to throw a sensible shadow. When telescopically examined, the surface of Jupiter is found to be marked with a series of dusky streaks, commonly known as the “ belts.” These belts vary greatly in form, size, and number from time to time. Occasionally only two or three broad ones are seen, at other times as many as eight, ten, or even a dozen narrow ones. Their physical nature is not well understood, but they are usually considered to be masses of cloud, acted upon in a manner in some way analogous to our terrestrial trade-winds, If this is the true hypothesis, as probably it is, then the planet has wind, rain, water and clouds, and is consequently fitted for the existence of animal and vegetable life. The existence of the belts was first detected by Zuppi, at Naples, in May 1730, though a claim has been put in on behalf of Torricelli.

Aberration. — The aberration of light is another important phenomenon which requires to be taken into consideration in the reduction of rough astronomical observations. Although light travels with the enormous velocity of 192,000 miles per second—a speed so great, that for all practical terrestrial purposes we may consider it to be propagated instantaneously; yet the astronomer, who has to deal with distances of millions of miles, is obliged to be more particular. A simple illustration will show this: the mean distance of our globe from the Sun is 95,000,000 of miles, and since light travels at the rate of 192,000 miles, we can ascertain by a simple arithmetical process that the time occupied by a ray of light reaching us from the Sun is 8m. 18s., so that in point of fact, in looking at the Sun at a given moment, we do not see it shining as it is, but as it did 8m. 18s. previously. If the Earth were at rest, this would be all very well; but since the Earth is in motion, when the solar ray enters the eye of a person on its surface, he will be some way removed from the point in space at which he was situated when the ray left the Sun; he will consequently see that luminary behind the true place it actually occupies when the ray enters his eye.

When an inferior planet is in superior conjunction, and “has a latitude or distance from the ecliptic less than the Sun's semi-diameter, it will be less distant from the Sun's centre than such semi-diameter, and will therefore be within the Sun's disc. In this case, the planet being between the Earth and the Sun, its dark hemisphere being turned towards the Earth, it will appear projected upon the Sun's disc as an intensely black round spot. The apparent motion of the planet being retrograde, it will appear to move across the disc of the Sun from east to west, in a line sensibly parallel to the ecliptic.” Such a phenomenon is called a transit, and as it can only occur in the case of the inferior planets, or those which pass between the Earth and the Sun, it is limited to Vulcan, Mercury, and Venus. The observations of these planets are used in a manner which we cannot here explain, for the purpose of ascertaining the distance of the Earth from the Sun.

James Gregory (inventor of the reflecting telescope which bears his name) seems to have been the first to point out this application of transit observations.

When any celestial object is concealed by the interposition of another, it is said to be occulted, and the phenomenon is called an occultation. Strictly speaking, an eclipse of the Sun is an occultation of that luminary by the Moon, but usage has given to it the exceptional name of “ eclipse.” The most important phenomena of this kind are the occultations of the planets and larger stars by the Moon, but the occultation of one planet by another, on account of the rarity of such an occurrence is exceedingly interesting. Inasmuch as the Moon's apparent diameter is about ½°, it follows that all stars and planets situated in a zone extending ¼° on each side of her path, will necessarily be occulted during her monthly course through the ecliptic. The great brilliancy of the Moon entirely overpowers the smaller stars, but the disappearance of the more conspicuous ones are visible in a telescope, a table of which is inserted every year in the Nautical Almanac.

It must be remembered, that the disappearance always takes place at that limb of the Moon which is presented in the direction of its motion.

In this chapter we shall briefly advert to a few historical remarks, relating to cometary astronomy.

Going back to the early ages of the world, we find that the Chaldæans considered comets to be permanent bodies analogous to planets, but revolving round the Sun in orbits so much more extensive, that they were therefore only visible when near the Earth. This opinion, which, by the by, is the earliest information we have of there being periodical comets, was also held by the Pythagorean school of philosophers. Yet Aristotle, who records this, insists that comets are merely mundane exhalations, carried up into the atmosphere, and there ignited.

Anaxagoras, Apollonius, Democritus, and Zeno considered that these bodies were formed by the clustering of many smaller planets.

It is a somewhat remarkable fact, that Ptolemy, so celebrated for his varied astronomical attainments, should nowhere have made any mention of comets; his omission is, however, made up for, by Pliny, who seems to have paid much attention to them. He enumerates 12 kinds, each class deriving its name from some physical peculiarity of the objects belonging to it.