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air. The desideratum in the manufacture of gunpowder is to generate a large quantity of gaseous matter at a high temperature. This is secured by combining six parts of nitrate of potash with one part each of sulphur and charcoal. When fired, the niter, by its decomposition, furnishes oxygen, which combines with the carbon, forming carbonic acid; the sulphur at the same time combines with the potash, thus generating nitrogen and carbonic acid gases; and these, at the moment of explosion, occupy more than a thousand times the volume of the powder from which it is formed. Here again is an instance of the power of man to set in order a train of causes, existing elementally in nature, which has produced the most extraordinary results. The discovery of gunpowder has exerted a mighty influence on the history of civilization. It has mitigated the barbarities, and diminished the fatality, of warfare. It has extended the geographical area of educated nations, and it has, in reality, been eminently serviceable to the interests of peace.*

The freezing of water inside red hot crucibles is another striking example of the power of intelligent man so to adjust and collocate natural laws as to produce results which nature alone could never have produced. The "spheroidal condition" of liquids in contact with heated surfaces, upon which the success of the experiment depends, is, of course, a natural law. But the placing of sulphurous acid in the red hot crucible, (which, in reality, does not come in contact with the hot crucible, in consequence of its having assumed the spheroidal state, and thus being surrounded by a cushion of elastic vapor,) and the placing of water on the sulphurous acid, which is instantly converted into ice, is the act of man. Man's increasing knowledge of the laws of nature has been constantly accompanied by advancing power over nature; and the author of "The Reign of Law" anticipates the final and complete subjugation of all nature to the intelligence of man.

Every student of chemistry is aware that man has been able to produce new substances-substances not found in nature— which are of the utmost value in manufactures, medicine, and the arts. He does not need to be informed that iodide of potash, iodide of mercury, nitrate of silver, and numberless

• See Buckle's "History of Civilization," pp. 146-150, vol. i.

[April, other substances, are not found in nature; that nitric acid, bichromate of potash, alcohol, so extensively used in manufactures, are not natural products; and that chromate of lead, (yellow,) oxide of lead, (red,) arsenite of copper, (Paris green,) and the aniline colors, (the finest purples and violets,) are all creations of chemical skill.

It is scarce necessary to direct attention to the control which man exerts over the electrical and magnetic forces. The achieve. ments of the Electro-Magnetic Telegraph are known to all our readers. The Atlantic cable needs only to be supplemented by a Pacific cable, and man may bid the subtle, and invisible, and immaterial power to convey his messages to the ends of the earth, and around the world.

V. The influence which man, by his intelligence, exerts over the vegetable life of the globe.

Remarkable changes, and astonishing modifications in the development of vegetable life, have been effected by man. He has transferred plants from their original habitat, placed them in new conditions of light, temperature, and soil, and they have undergone changes in consequence so great as scarcely to be recognized as the same species. One of the most obvious changes resulting from the agency of man is an increase in the size of the cultivated plant. This change is strikingly exhibited in the parsnip and the carrot. The woody, spindly root of the Daucus carota has been transformed into the large, juicy, Arlington carrot. Not only has the size of the entire organism been changed, but the relative development of the individual parts of the plant has been greatly modified by the agency of Thus cultivation converts a single into a double flower, as in the rose and the dahlia. In fact every natural flower is single, and wherever we have a double flower it is the result of cultivation. Cultivation also obliterates spines, and prickles, and thorns, a change which Linnæus designates "the taming of wild plants," and of which we have examples in the apple and the plum. A great number of plants which, in their natural state, were creepers, and trailed upon the ground, when cultivated have reared their stalks and stand erect; while others that were annuals become perennial, and biennials have become annuals.

man.

Remarkable changes have also been effected in the color of flowers by the agency of man. Placing charcoal around the roots has darkened and enriched the colors of the dahlia, the rose, and the petunia. Carbonate of soda reddens the ornamental hyacinth; and super-phosphate of soda alters, in various ways, the hue and bloom of other cultivated plants. The Hydrangea Hortensis has been changed from red to blue; and Mr. Herbert asserts that from a red cowslip he has raised a primrose, an oxlip, a polyanthus, and a hose-in-hose cowslip. The statement of Mr. Herbert has been confirmed by the experiments of Prof. Henslow, of Cambridge.*

Fruits have also been astonishingly developed, and modified in color and in flavor, by the action of man. The crab has been transformed into an apple, and varieties have been multiplied without limit. In 1850 more than fifteen hundred varieties had been enumerated. The sloe has been converted into the plum; the Pulsica Vulgaris, a native of Persia, into the peach, of which we have now two hundred varieties. And such a command over nature has man acquired in this department, that it is claimed "he can command any flavor of the fruit he may desire."+

Perhaps one of the most wonderful transformations is that of Brassica Oleracea. Its native habitat is the sea-coast, where it is a bitter, acrid plant. Man has transferred it to a more wholesome soil, and it has lost its saltness, and been metamorphosed into three vegetables as distinct from each other as they are unlike the parent plant-the cabbage, the cauliflower, and the broccoli. Our gardens, in fact, are full of such vegetable transformations; not so marked and striking, perhaps, as the Brassica Oleracea, but still such as to impress us with a sense of the amazing power which man wields in the direction and government of natural laws. Our cultivated potatoes, in all their variety of color, size, and flavor, have been produced by man from a tiny, bitter root, which has its native home on the sea-coast in Chili.

These instances may be taken as illustrations of the power of man to modify, and indeed materially alter, the vegetable life on the globe. In this department he has produced results

*See Lyell's "Principles of Geology," p. 590.
+"Cottage Gardener."

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which nature alone could never have produced. Nature alone never produced a double rose, or a Rhode Island Greening, or a Lawton Blackberry, or a Cuyahoga Grape. These are results of man's action upon nature. They show that nature is flexible to the hand of intelligent man.

VI. The influence of man on the physical development, habits, and instinct of animals.

The power of man to control, modify, and subordinate nature, has been strikingly exhibited in this department. In animal organisms, as well as vegetable, there is a remarkable susceptibility to the external conditions of climate, food, domestication, and the like, so as to present a remarkable deviation from general uniformity. Peculiarities sometimes arise, to all appearances de novo, originating in causes which are scarcely appreciable. Many of these deviations and peculiarities are rendered perpetual by hereditary transmission.

Selecting those animals which have the most flexible frame and constitution, and which even Professor Owen regards as "having been predestinated and prepared for man," he has for ages been conducting experiments in varying their forms, modes of life, and instincts, so as to make them more fully subservient to his use and pleasure. And the amount of his success has been amazing. Animals have been altered in size and materially changed in form, as may be seen by comparing the Shetland pony with the Arabian race-horse, which have unquestionably a common origin; and the Italian grayhound with the Newfoundland dog, which are undoubtedly of one species. Instincts have been obliterated, or rendered dormant, as in the horse; and new instincts or habits have been induced and become hereditary, as in the Pointer and Retriever dogs.

Dogs are all, unquestionably, of one species, and have therefore had one common origin. This is asserted by every naturalist of note, from Baron Cuvier to Professor Owen. The number and relation of the bones are the same in all the varieties of dogs; the form of the teeth is the same, the period of gestation is the same, and when they have run wild, as in Cuba and South America, the varieties have disappeared, and they have returned to the common form. Now let any dog-fancier before his mind all the varieties with which he is

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acquainted, and he will see how man has strangely and marvelously modified nature by his knowledge and control of nature's laws. For in nature we shall seek in vain for the Scotch Terrier, the Shepherd's dog, the Italian Grayhound, the Newfoundland dog, the Pointer, the Retriever, and others which might be named. These forms and characteristics belong to the sphere of domestication and civilization. They have been superinduced on the flexible nature of the species by the genius of man.

The habits of the dog have been altered in a noteworthy manner by his association with man. In a wild state the dog is gregarious, hunting in packs of fifty or more. In the domestic state he takes on him the peculiar individuality of his master, prefers his society, and drives other dogs from the premises. The wild dogs of South America, and the Gingo of Australia, do not bark. Barking is an acquired, hereditary instinct, and probably originated in the attempt to imitate the human voice. Peculiar faculties also are developed in the domestic dog which are not displayed in a state of simple nature. Some, as the Shepherd's dog, will drive home a flock of sheep; he will take all precaution to prevent their scattering, and readily bring back the wanderers; he will even keep two flocks from mingling, and if mixed, will separate them. The Setting dog will find and start the game; the Pointer will stop and indicate the position of the game, and the Retriever will gather it up and bear it to his master. These qualities, which at first are the result of education, soon become hereditary, so that the young dog, on being taken for the first time into the field, will behave as well as its parent.

The same remarks are equally applicable to the various breeds of horses, oxen, and sheep. All horses are of one species, yet how do they differ in size, build, temper, and physiognomy, from the Shetland pony to the Arabian racer. "Of all the quadruped servants of man, none has proved of more value to him, in peace or in war, than the horse: none have co-operated with the advancing races more influentially in man's destined mastery over the earth and its lower denizens. In all the modifications of the old palæotherian type to the end, the horse has acquired nobler proportions and higher faculties; more strength, more speed, with amenability to the bit. As such, I

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