A Catechism of Familiar Things Part 23

CHAPTER XII.

SPECTACLES, MARINER'S COMPa.s.s, BAROMETER, THERMOMETER, WATCHES, CLOCKS, TELESCOPE, MICROSCOPE, GUNPOWDER, STEAM ENGINE, AND ELECTRO-MAGNETIC TELEGRAPH.

When were Spectacles invented, and who was their inventor?

It is supposed that they were first known about the thirteenth century, and invented by a monk of Pisa, in Italy, named Alexander de Spina. Spectacles are composed of two circular pieces of gla.s.s set in a frame.

What are these gla.s.ses called?

Lenses. They are either convex or concave, according to the kind of sight requiring them. Old people, and those who can only see things at a distance, from the flatness of the eye, which prevents the rays of light converging so as to meet in the centre, require convex lenses.

People who can only distinguish objects when viewed closely, from the eye being too convex, require concave lenses to counteract it by spreading the rays, and thus rendering vision distinct.

_Convex_, rising outwardly in a circular form; opposite to concave.

_Concave_, hollow; round, but hollow, as the inner curve of an arch, &c.

_Converging_, tending to one point from different parts.

_Vision_, the faculty of seeing.

What is the Mariner's Compa.s.s?

A most useful and important instrument, by the aid of which the navigator guides his s.h.i.+p on the sea, and steers his way to the place of his destination. The inventor of the Mariner's Compa.s.s is not known, nor the exact time of its introduction; it was employed in Europe in navigation about the middle of the thirteenth century, and has been in use more than five hundred years. The Chinese are said to have been acquainted with it much earlier, but no reliance can be placed on their dates. The power of the loadstone to attract iron was known to the ancient Egyptians, but it was not applied to any practical purpose.

_Navigator_, one who guides a s.h.i.+p.

_Steer_, to direct or guide a vessel in its course.

_Destination_, the place to which a person is bound.

_Practical_, capable of practice, not merely speculative.

What is the Loadstone?

An ore of iron which possesses the peculiar property of attracting iron, namely, of drawing it in contact with its own ma.s.s, and holding it firmly attached by its own power of attraction. A piece of loadstone drawn several times along a needle, or a small piece of iron, converts it into an artificial magnet; if this magnetized needle is carefully balanced, it will turn round of itself, till its end points towards the North. The magnetized needle also possesses the power of attracting iron, and of communicating this power to another piece of iron or steel, similar to that of the loadstone itself.

_Contact_, touch.

_Magnetized_, rendered magnetic.

Describe the Mariner's Compa.s.s.

The Mariner's Compa.s.s consists of a circular box, enclosing a magnetized bar of steel, called the _needle_, carefully balanced on an upright steel pivot, and having that end which points to the North shaped like the head of an arrow; attached to this needle, and turning with it, is a card on which are printed the divisions of North, South.

East, and West; called the points of the compa.s.s. By simply looking at the position of the needle, the mariner can see the direction in which his vessel is sailing, and regulate his helm accordingly.

_Helm_, the instrument by which a s.h.i.+p is steered, consisting of a rudder and tiller.

What is a Barometer?

An instrument for measuring the weight of the atmosphere, which enables us to determine the changes of the weather, the height of mountains, &c. It consists of a gla.s.s tube hermetically sealed at one end, filled with mercury, and inverted in a basin of mercury; according to the weight of the atmosphere, this mercury rises or falls.

How is the Hermetic seal formed?

By heating the edges of a vessel, till they are just ready to melt, and then twisting them closely together with hot pincers, so that the air may be totally excluded. The word is taken from Hermes, the Greek name for Mercury, the heathen G.o.d of arts and learning, and the supposed inventor of chemistry,[9] which is sometimes called the hermetical art; or perhaps from Hermes, an ancient king of Egypt, who was either its inventor, or excelled in it.

[Footnote 9: See Chapter XVIII., article Chemistry.]

What is Mercury?

Quicksilver, or mercury, is a white fluid metal, the heaviest except platina and gold; it readily combines with nearly all other metals, and is used in the manufacture of looking-gla.s.ses, barometers, thermometers, &c.; in some of the arts, and in the preparation of several powerful medicines. It is found in California, Hungary, Sweden, Spain, China, and Peru. The quicksilver mine of Guanca Velica, in Peru, is one hundred and seventy fathoms in circ.u.mference, and four hundred and eighty deep. In this profound abyss are seen streets, squares, and a chapel, where religious wors.h.i.+p is performed. The quicksilver mines of Idria, a town of Lower Austria, have continually been wrought for more than 300 years. The vapor which is continually arising from the mercury is very hurtful to the miners, who seldom survive many years.

_Abyss_, a gulf, a depth without bottom.

In what state is Mercury usually found?

Either native, or in the form of ore; it is often found mixed with silver, but more frequently with sulphur in the form of sulphuret, which is decomposed by distillation. Running mercury is found in globules, in America, and is collected from the clefts of the rocks.

Mercury has the appearance of melted silver; it is neither ductile nor malleable in this state; it is a substance so volatile, when heated, that it may be evaporated like water; it is always seen in a fluid state, even in temperate climates, as a very small portion of heat is sufficient to preserve its fluidity. It is used to separate gold and silver from the foreign matter found with those metals. Calomel, a valuable medicine, and vermilion, a color, are both preparations of mercury.

_Globules_, small particles of matter having the form of a ball or sphere.

What is a Thermometer?

An instrument for measuring temperature. It consists of a fine gla.s.s tube, terminated at one end in a bulb, usually filled with mercury, which expands or contracts according to the degree of heat or cold. On the scale of the Fahrenheit thermometer, the freezing point of water is marked 32 and the boiling point at 212. In both the Centigrade and the Reaumur scales the freezing point is at 0, and the boiling point at 100 in the Centigrade and at 80 in Reaumur's. The invention of this instrument dates from about the close of the sixteenth century; but it is not known by whom it was first brought into use.

_Terminated_, finished, ended.

When and by whom were Watches and Clocks invented?

Watches were invented about the year 1500, but who was the inventor is disputed. They were, however, of little value as time-keepers, before the application of the spiral spring as a regulator to the balance; the glory of this excellent invention lies between Dr. Hooke and M.

Huygens; the English ascribing it to the former, the Dutch, French, &c., to the latter. Some a.s.sert that pocket-watches were first made about 1477, at Nuremberg, in Germany. The most ancient clock of which we possess any certain account, was made in 1634 by Henry de Wycke, a German artist; it was erected in a tower of the palace of Charles V., king of France. The pendulum was applied by Huygens, in 1656.

What is a Pendulum?

A weight so suspended from a fixed point that it may easily swing backward and forward; its oscillations are always performed in equal times, provided the length of the pendulum and the gravity remain the same. It is said that the idea of employing the pendulum for the measurement of time, was first conceived by Galileo, while a young man, upon his observing attentively the regular oscillations of a lamp suspended from the roof of a church in Pisa. It was not, however, till the time of Huygens that a method was devised of continuing its motions, and registering the number of its oscillations.