OPEKA-GLASS                                          1386                                                        OPIUM

Opera=Glass, an instrument for making distant objects appear brighter and more distinct. An ordinary opera-glass is essentially two telescopes, of the type employed by Galileo, so mounted in one frame as to produce two images of the same size, one for each eye. The principle of the opera-glass is that of the astronomical telescope, except that the latter uses a converging eyepiece, while in the opera-glass a diverging eyepiece is used. The reason for this difference is twofold : The diverging eyepiece gives an upright image; and the total length of the opera-glass is the difference between the focal lengths of the object lens and the eye lens. This makes the opera-glass short, so that it can be easily carried in the pocket. If a converging eyepiece were used, the distance between the objective and the eye lens would have to be equivalent to the sum of their focal lengths, which would make

the instrument unwieldy. The optical behavior of the opera-glass will be clear from the accompanying figure, where Bt B3 indicates the object glass, through which pass three rays from a very distant object P. The pupil of the eye is indicated by p p, and the image of P is seen erect in the direction indicated by the three rays Pt. The principal focus of either lens falls at some point within the eye. The angle which the image subtends at the eye is much greater than that under which the object is seen with the naked eye. Zeiss of Jena has recently introduced an enormous improvement into the ordinary opera-glass, by using

(instead of two Galilean telescopes) a pair of astronomical telescopes. But he avoids the difficulty of extreme length, mentioned above, by placing a pair of prisms between the two lenses, such as is shown in the accompanying figure. The path of the ray between the two lenses is thus doubled upon itself, securing a short length for the instrument and at the same time giving an erect image and a large, clear field. These prisms allow him also to place the two objectives a foot or so apart, while the eye lenses are at a distance suited to the eyes. Equipped with such a glass, a field officer can stand behind a tree in safety while he is watching

the operations of the enemy. It need hardly be added that the armies and navies of all civilized countries are now furnished with these glasses.

Ophir (ō'/ēr), a place mentioned in the Bible, from which the navy of Solomon brought gold, precious stones and sandalwood. The voyage took three years. It was on the eastern coast of Africa, in Arabia or in India, but in which is doubtful. Jose-phus places it on the peninsula of Malakka.

O'pium is the dried juice of the unripe seed-vessels of a kind of poppy. The poppy is cultivated in India, Persia, China, Turkey and Egypt. It requires a very rich soil, and irrigation is often used as an aid to cultivation. The main opium district in India is a large tract on the Ganges, about 600 miles long and 200 broad. In India the seed is sown in November, the plant blossoms in January or later, and in three or four weeks after, when the poppy heads or capsules are about as large as a hen's egg, the field is ready for work. The collector takes a small instrument made of four little knives tied together, looking like the teeth of a comb, and with this cuts or scratches the poppy heads. This is done in the afternoon, and the next morning a milky sap can be collected from the heads by scraping with a kind of scoop into an earthen vessel. The vessel is kept turned on its side so that any watery fluid may drain out, and as the juice dries it is turned often, so that it will dry equally. It takes three or four weeks before it is thick enough to be used in the factories. It is then thrown into great vats in the factories and kneaded, and made into balls or cakes', which are dried and packed in chests for the market. Opium has a bitter taste and a peculiar, heavy odor. It is poisonous, but makes a most valuable medicine, in which form it is used to allay pain and produce sleep. The habitual use of the drug is known as opium-eating or the opium habit, and is made use of to relieve pain or sleeplessness, when it soon becomes a habit most difficult to overcome. The amount usually taken is about three grains a day, though De Quincey (himself a slave to the habit) says that he used sometimes 8,000 drops of laudanum (a form of opium) daily. Tt acts as a stimulant, followed by depression and nervousness, requiring a fresh dose to remove them. Another way in which it is used is in smoking, a practice most common in China and in India. The opium prepared for smoking is called chandu, and is a watery extract about twice as strong as the drug. A piece of opium as large as a pea is placed in a small cup at the end of a pipe and lighted, and the smoke inhaled. The opium is distilled by the process, and there is very little morphine in the smoke. There are said to be a million opium smokers in the United States. Excessive use of it wrecks the constitution

Description images/pp0277 1

fig. 1

Description images/pp0277 2

fig. 2