Page:Popular Science Monthly Volume 26.djvu/151

Rh rarer metals, the oxygen-furnace, and the atmospheric gas-furnace, and, in its incipient stage, the electrical furnace. The success of air-refrigerating machines and the economic distillation of sea-water arc dependent on the same knowledge. Engineering and electrical science are brought into close relations in the construction of telegraph and cable lines, in the development and application of dynamo-machines and dynamo-energy, and in electric lighting, telephony, and microphony. In navigation, the engineer avails himself of optical science in the equipment of lighthouses; of pneumatics in Sir William Thomson's apparatus for taking quick soundings, and of magnetic science in his adjustment of improved compasses. Mathematical principles enter into the construction of ship-models. In the processes of the preparation from the ore of various metals, "it is essential that the engineer and the chemist should either be combined in one and the same person, or go hand in hand." The chemist and the microscopist have to be called in to ascertain the purity of every contemplated source of water-supply; and the chemist, when it is desired to convert a hard water into soft. Engineers must consult the geologist before they can intelligently make estimates of the works they are about to undertake. In biology, the engineer learns from the botanist the qualities of the various woods he occasionally uses in his work, and has the "germs" in view in arranging for the purity of water-supply and for ventilation. Lastly, great works of engineering facilitate geographical exploration, and are called into existence by the dictates of the economist. The speaker closed his address with a tribute to the memory of Sir William Siemens.

Cultivation of Cacao,—The cacao-tree flourishes in the hot regions of America, and has been cultivated since the conquest in Mexico, Guatemala, and Nicaragua. To secure success, the cacao-plantation must be made in new land, for the tree requires a rich, deep,' and moist soil, and heat. The best situation is cleared forest-land, so inclined as to permit its being irrigated. The cultivation of the trees often ceases to be profitable when the temperature falls below 73°. The cacao seldom blossoms till it is thirty months old. The planters destroy the first flowers, in order to prevent fruiting before the fourth year. There are few plants in which the flower is so small and so disproportioned to the size of the fruit. A bud measured by M. Boussingault, at the time of its expansion was not more than four millimetres broad. The flesh-colored corolla was composed of ten petals surrounding five silver-white stamens. The flowers did not appear singly, but in bouquets on every part of the trunk, on the principal branches, and even on the salient wood-roots. The fruit comes to maturity in about four months after the fall of the flowers. It is about ten inches long and three or four inches in diameter, slightyslightly [sic] curved, weighs three hundred or five hundred grammes, and is divided into three lobes. Its color varies from a greenish-white to a red-violet. The pericarp is furrowed longitudinally within; the flesh or pulp is rosy-white and acid, and generally envelops twenty fine, white, oily kernels which in drying assume a superficial brown tint. Two principal crops are harvested every year, but on large plantations the gathering is going on all the time, and it is not uncommon to see trees bearing both flowers and fruits at the same time. After breaking the shell, the nuts are taken out and exposed to the sun. In the evening they are piled up under a shed. An active fermentation soon sets in, which must not be allowed to go too far, and, accordingly, the nuts are on the next day spread out in the air. The cultivation of a cacao-plantation does not demand much labor. One man can take care of a thousand trees. The most serious difficulties are the dangers from storms, which are very destructive to the fruit; otherwise the principal duty of the attendant is to protect the crop from animals. The cacao is shelled by roasting at a moderate heat, in which process it acquires, like the coffee-bean, an odor arising from a minute proportion of a volatile principle which it contains. This is the peculiar aroma which we perceive in chocolate. The cacao-beans are rich in nutritious principles, containing a fat, nitrogenous substance analogous to albumen and caseine, theobromine and ternary compounds, all of which vary somewhat in their relative quantities. The theobromine is almost identical with the caffeine of coffee and the theine