of the effects produced by a scientific management of these powers, of which none are more curious than

the tales of Dionysius'

66

Ear," as it was termed,

although in this case science was sadly perverted

to the vilest of purposes.

CHAPTER VIII.

NAVIGATION-LATITUDE.

"Give me the way of wandering stars to know,

The depths of heav'n above, and earth below;

Teach me the various labours of the moon,

And whence proceed the eclipses of the sun."-DRYDEN.

AMONGST the various sciences which tend to the happiness of man, by increasing his comforts and adding to his luxuries, that of Navigation stands pre-eminent; and we have devoted a chapter to its consideration, as placing before our view the benefits resulting from a habit of reflection. Astronomy, on which the science of navigation is founded, is of very remote origin, and has ever been the favourite study of those whose occupations have led them to spend much of their time in the open air, more especially in the night season; and consequently we find the shepherds who watched their flocks in the early ages on the plains and mountains of Asia, to have made considerable acquirements in the knowledge of the movements of the heavenly bodies, though mixed

with much error. They observed the course of the planets, and gave names to the various constellations of stars, and thus laid the foundation for an acquaintance with those sublime wonders, which cannot be contemplated without enlarging and elevating the mind beyond the limits of our present state of existence; hence we find the pastoral life to have abounded with examples of piety and simplicity,for what can more conduce to a pure and simple mind, than the pervading feeling of the immediate presence of the Deity, which the constant study of His sublimest works, far from the busy haunts of men, and in the stillness of night, must produce?

To this study, then, the art of navigation owes its origin; for, from a knowledge of the motions and situations of the planetary system, the mariner is enabled, when his bark is heaving on the billows of the interminable waste of waters, far from land or any object to mark his situation, to tell, with unerring certainty, the exact place on that trackless, boundless plain, where he is situated so that he can mark on his map the spot where he is, and thence learn, from the sad experience of former navigators, to avoid those hidden rocks and shoals on which they have made shipwreck, and to shape his course for his destined haven. Astronomy is, in short, to the mariner what the direction-post is to the weary traveller on the desert heath.

On a cursory glance, it appears wonderful that observations made on the heavenly bodies, which are situated so many millions of miles distant from us, should enable us to ascertain, to a very great nicety, our situation on the earth; but such is nevertheless the case; and we hope, without entering into the minutiae of the subject, to give our readers an insight into the theory of the science.

The earth has been surrounded by geographers by a number of ideal lines or rings, encircling it at regular distances, from the equator to the poles; these are called parallels of latitude, and are numbered from 0 to 90, the distance between the equator to the pole being divided into 90 parts or degrees : the ring next to the equator is called the first degree of latitude; the next, the second degree; and so on till we arrive at the pole, or 90th degree of latitude. These divisions are again crossed by a like number of lines running from pole to pole, called lines of longitude; the one which, in its passage from the north to the south pole, passes through Greenwich Observatory is termed the meridian of Greenwich, and in England each separate line is counted as so many degrees to the east or west of Greenwich. The globe is thus divided into a number of small compartments. Now if we can first determine on what parallel of latitude we are placed, that is, our position as far as regards north and south; and if we

can then also determine on what line of longitude we are situated, that is, our situation as regards east and west; the intersection of these two lines will be the position required.

The diagram, which represents half a globe, surrounded by these ideal circles, in which the horizontal ones represent parallels of latitude, and the perpendicular ones lines of longitude, will at once render this obvious.

We will first turn our attention to latitude. To assist him to determine this, the mariner is provided with an instrument called a sextant, or quadrant, which enables him to determine accurately the