Part 5

When the liquid is poured out of a vessel in the air it is rapidly converted into gas. The great lowering in the temperature causes a condensation of the moisture of the air in the form of a cloud. The same thing is seen when the cover is removed from a can containing the liquid. Of course, this liquid does not wet things as water does. When, however, as happened in New York, the lecturer deliberately pours a dipperful of the liquid upon a priceless Worth gown, he may expect to hear expressions of horror from the owner. This experiment passed off most successfully. Every trace of the liquid air was converted into invisible gases before the fleeting agony of the sympathetic audience had passed away.

The effects of very low temperature upon a number of substances have been studied, and some of them can easily be shown. Paraffin, resin, and rubber immersed in liquid air soon become very brittle, and the color of the resin is completely changed. A beefsteak or an onion also becomes brittle, and can be broken into small fragments by the blow of a hammer. A similar effect is produced in the case of some metals. Tin and iron, for example, become brittle, and the tenacity of the iron is greatly increased. A copper wire, however, retains its flexibility. At low temperatures the electric conductivity of all metals is increased. In general, the lower the temperature the greater the conductivity. If a copper wire could by any means be kept cold enough, electrical energy could be transmitted by it with but little loss--perhaps none. Mercury is easily frozen by surrounding it with liquid air, and the solid thus formed is very hard, though if it is cooled down sufficiently it becomes brittle.

Alcohol can be frozen without difficulty by means of liquid air. By the aid of the lowest temperatures hitherto attainable it has only been possible to convert alcohol into a pasty mass. The frozen alcohol is as hard as ice. When alcohol is dropped into liquid air the drops retain the globular form. When taken out on a platinum loop the flame of a Bunsen burner does not set fire to it.

Phosphorescence is greatly increased by cooling substances down to the temperature of liquid air. This has been shown by means of water, milk, paper, eggs, and feathers. An egg and a feather could be distinctly seen in a dark room.

Scarlet iodide of mercury is converted into the yellow variety when it is subjected to the temperature of liquid air. Some other colors are changed under the same circumstances, but not enough is known of this subject to warrant a general statement.

Attention has already been called to the fact that liquid air loses its nitrogen more rapidly than it does its oxygen, and that, after a time, the residue contains a large proportion of oxygen. As combustion is combination with oxygen, combustion or burning takes place more readily in contact with this liquid oxygen than it does in the air. If a lighted match is attached to the end of a steel watch spring, and this then plunged beneath the surface of liquid air, the spring will soon take fire and burn brilliantly, the sparks flying off for some distance in beautiful coruscations. Hair felt, which does not burn in the air, burns in a flash when soaked with liquid air. Finally, when liquid air is confined in any vessel not capable of sustaining an enormous pressure, say about ten thousand pounds to the square inch, the vaporization goes on until the vessel bursts or the stopper is forced out. It might therefore be used as an explosive without any addition, but its manipulation is not altogether simple.

Now for the inevitable question: Of what use is liquid air likely to be? This is a perfectly proper question, and yet, if scientific workers always stopped to ask it, and would not work unless they could find a favorable answer, progress would, to say the least, be much slower than it is. Most great practical discoveries have necessarily passed through the plaything stage. Some of the most important discoveries have not even furnished playthings, and have found no practical applications as this expression is commonly understood. But the production of liquid air, while furnishing mankind with a beautiful and instructive plaything, seems likely to find practical applications. We may look for these in four directions, to each of which a short paragraph may be devoted:

First, as a cooling agent. Low temperature is marketable. To be sure, the demand for the extremely low temperature that can be produced by liquid air does not exist to-day, but this concentrated low temperature can be diluted to suit conditions. The only question to be answered in this connection is, then, What is the cost of cold produced by liquid air? It is impossible for any one to answer this question at all satisfactorily at present. It can only be said that this is what experimenters are trying to find out. It appears, however, that they are on the way to cheap liquid air, and that as the processes are improved the price will become lower and lower.

Second, for the construction of motors. There is no doubt that liquid air with its enormous power of expansion can be used as a source of motive power just as compressed air is. In the case of steam it is necessary to heat the water in order to convert it into steam, and to heat the steam to give it the power of expansion. The cost is, in the first instance, that of the fuel. Given a certain amount of heat, and a certain amount of work is obtained. If liquid air is used, the problem is much the same. Engines must be run in order to compress the air which is to be liquefied. Every gallon of liquid air has been produced at the expense of work of some kind. Now, the question arises at once, What proportion of the work that was put in that gallon of liquid air in the course of its production can be got out of it again? It is certain that all of it can not be got out unless all that we have ever learned about such matters goes for nothing. In dealing with the problem of the application of liquid air as a source of motive power we are therefore doubly handicapped. In the first place, we do not know the cost of the liquid when produced on the large scale; and, in the second place, _we_ do not know the probable efficiency of a liquid-air motor. I say "we do not know." Perhaps Mr. Tripler and the others engaged in the experiments on this subject do know approximately. We certainly can not blame them for not telling us all they know at this stage of the work. It is unfortunate, however, that such a statement as was recently published in a popular magazine should be allowed to gain currency--apparently with the sanction of Mr. Tripler. The statement referred to is to the effect that ten gallons of liquid air have been made by the use of three gallons of liquid air in the engine. If that means that the ten gallons of liquid air are made from air at the ordinary pressure, the statement is in direct conflict with well-established principles. If it means that the ten gallons of liquid air are made from air that has already been partly compressed, we must know how much work has been done before the liquid-air engine began. Leaving out of consideration the question of cost, it may be pointed out that liquid-air engines would have the advantage of compactness, though they would necessarily be heavy, as they would have to be strong enough to stand the great pressure to which they would be subjected.

The third application of liquid air that has been suggested is in the preparation of an explosive. In fact, an explosive has been made and used for some time in which liquid air is one of the constituents. When the liquid from which a part of the nitrogen has boiled off is mixed with powdered charcoal, the mixture burns with great rapidity and great explosive force. "To make this explosive, Dr. Linde pours the liquid containing about forty or fifty per cent of oxygen on fragments of wood charcoal, two or four cubic millimetres in size. These are kept from scattering under the ebullition of the liquid by mixing them into a sort of sponge with about one third of their weight of cotton wool." Of course, this explosive must be made at or near the place where it is used. It has been in use in the way of a practical test in a coal mine at Pensberg, near Munich. It is claimed that the results were satisfactory. The chief advantage of the explosive is its cheapness, and the fact that it soon loses its power of exploding.

Finally, the fourth application of liquid air is for the purpose of getting oxygen from the air. This can be accomplished by chemical means, but the chemical method is somewhat expensive. Oxygen has commercial value, and cheap oxygen would be a decided advantage in a number of branches of industry. It will be observed that it is the liquid oxygen that makes possible the preparation of the explosive described in the last paragraph. Oxygen as such in the form of gas is of value in Deacon's process for the manufacture of chlorine. In this process air and hydrochloric acid are caused to act upon each other so as to form water and chlorine. The nitrogen takes no part in the act, and it would be an advantage if it could be left out. It is only the oxygen that is wanted. There are many other possible uses for oxygen either in the liquid or in the gaseous form, but these need no mention here.

In conclusion it may safely be said that it is highly probable that liquid air will be found to be a useful substance, but it is impossible at present to speak with any confidence of the particular uses that will be made of it. As work with it is being carried on energetically in at least three countries, we may confidently expect important developments in the near future.

THE PHYSICAL GEOGRAPHY OF THE WEST INDIES.

BY F. L. OSWALD.

II.--BIRDS.

The abundance of birds on the four largest islands of the West Indian archipelago, where indigenous mammals are almost limited to rodents and bats, has often suggested the conjecture that the ancestors of those islanders must have been immigrants from the east coasts of the American mainland; and that theory seems to be confirmed by two facts: the identity, or similarity, of numerous Mexican and West Indian species, and the circumstance that those analogies include so many swift-winged birds.

There are no woodpeckers in the forests of the Antilles, and only two species of large gallinaceous birds, but a prodigious variety of pigeons, swallows, finches, and crows. The _alcedos_ (kingfishers) are scarce, but the blackbirds so numerous that some of the countless species seem to claim a South American and even transatlantic ancestry. The restless _estornino_ of the Cuban highland forests, for instance, might be mistaken for a varnished starling, resembling the _Sturnus vulgaris_ of western Europe in everything but the more brilliant luster of its plumage. The curious _codornilla_, or dove quail, too, has its nearest relatives on the other side of the Atlantic, in Syria, Arabia, and the foothills of the Atlas. It builds its nest on the ground and, judging from its appearance, would seem to form a connecting link between the doves and small _gallinæ_; but its wings are those of a pigeon, and with the assistance of a northeast gale may possibly have carried it across the ocean.

In studying the geographical distribution of animals, we may estimate the prevalence of special genera by the number of their varieties, or by the aggregate sum of individuals, and in the latter sense the migratory pigeons of our forest States once nearly outnumbered all the other birds of North America, though the family is limited to five or six species. But in the West Indies the _Columbidæ_ predominate in both respects. Cuba is a country of wild pigeons as pre-eminently as South Africa is a land of pachyderms and Madagascar of night monkeys. The _Columba leucocephala_ (a congener of our ringdove) inhabits the mountain forests in countless swarms, and at the end of the rainy season visits grainfields in such numbers that hundreds are sometimes captured in nets, by means of corn scattered along the furrows.

A closely allied variety is found in San Domingo, where in many upland regions a darkey, equipped with a shotgun and a supply of gunpowder, can dispense with agriculture and raise a family of anthropoids on pigeon pies and _tortillas_, compounded from the grain found in the crops of his victims.

But the _tittyblang_ (_tête-blanc_) has scores of smaller and larger cousins, culminating in the Cuban primate of the family, the splendid _paloma real_, with its coronet of pearl-gray plumes and dark-blue wings.

Ducks, too, must number some twenty West Indian species, and one kind of wild geese often obliged the rice planters to employ mounted sharpshooters, who galloped up and down the long dikes, yelling blasphemies, and every now and then enforcing their quotations with a handful of buckshot. But, for all that, the planter could think himself lucky to gather a sixty-per-cent harvest of the total produce, for experience soon enabled the long-necked depredators to estimate the target range of the _cazador_ within a dozen yards and take wing in the nick of time, only to resume their feast at the other end of the plantation.

A long-continued process of natural selection has also modified the habits of numerous species of West Indian parrots. Four hundred years ago, when Fernan Oviedo superintended the placer mines of Hayti, _loris_ were so abundant and tame that his assistants often amused themselves prowling about a thicket of berry bushes and capturing the chattering visitors by means of a common ring net. Nestlings could be taken from every hollow tree, and often from the thatchwork of deserted Indian cabins; but the overconfident specimens came to grief, and the survivors have learned to give the Caucasian varieties of the _Simia destructor_ a wide berth. They raise their young in the cavities of the tallest forest trees, and approach human habitations only at dawn of day and sometimes during the noonday heat, when creoles can be relied upon to indulge in a _siesta_ nap. In reliance on their protective colors, gray parrakeets frequent the dead timber of the coffee plantations, while the leaf-green Amazon parrot sticks to leaf trees.

"When they alight on a dry branch," says Captain Gosse, in his Jamaica chronicle, "their emerald hue is conspicuous and affords a fair mark for the gunner, but in a tree of full foliage their color proves an excellent concealment. They seem aware of this, and their sagacity prompts them to rely on it for protection. Often we hear their voices proceeding from a certain tree, or have marked the descent of a flock, but on proceeding to the spot, though the eye has not wandered from it, we can not discover an individual; we go close to the tree, but all is silent; we institute a careful survey of every part with the eye, to detect the slightest motion, or the form of a bird among the leaves, but in vain, and we begin to think that they have stolen off unperceived, but on throwing a stone into the tree a dozen voices burst forth into cry, and as many green birds dart forth upon the wing."

The gorgeous macaws, on the other hand, seem to owe their color contrasts to sexual selection. "Ya son vencidos los pavos de India"--"That does beat a Hindostan peacock"--exclaimed King Ferdinand, when Columbus introduced those most splendid products of the American tropics.

Nor can the exigencies of protection have evolved the glaring colors of the West Indian hornbill. The _toco_ (toucan), as the Cubans call the yellow-billed species, can be descried from a distance of two hundred yards, and is, indeed, not anxious to be admired at close range. Old specimens get as wary as mountain ravens, but, like crows, become ridiculously tame in captivity, and will follow their proprietors with loud croaks, every now and then opening their lunch-trap to indicate their desire for refreshment. They are, on the whole, the hardiest of all tropical birds, and can weather the winters of our coast towns as far north as Wilmington, in open-air cages, owing perhaps to their habit of extending their excursions to the high mountain ranges of their native land.

Economical Nature rarely wastes the gift of song on a bird of bright plumage, but it is less easy to understand why so many feathered beauties should have been afflicted with harsh and positively repulsive voices. The horrid screams of the peacocks, guinea hens, and macaws can hardly be supposed to charm their mates, and are too easily recognized to deter their natural enemies. But the roars (there is no more adequate word) of some species of hornbills would almost seem intended to serve the latter purpose.

"The voice of the _Buceros bicornis_," says Wallace, "can be plainly heard at a distance of a mile, so that the amazement of travelers visiting its haunts seems explicable enough. Its screams may be described as something between the bray of a jackass and the shriek of a locomotive, and are not surpassed in power by any sound that an animal is capable of making. They re-echo through the hills to such a degree that it is difficult to assign the noise to a bird, and are sometimes kept up so continuously as to become absolutely unbearable."

The condor and the harpy eagle have not found their way across the Caribbean Sea, but the West Indies boast three varieties of fish eagles, several species of mountain falcons, and a curious singing owl, the _oriya_, that chants its serenades in the plaintive strain of the whip-poor-will, and is dreaded by the Porto Rico darkeys as a bird of ill-omen:

"Grita l'oriya: Venga amigo, Venga conmigo a mi patria, Venga te-digo!"

Small hooting owls abound, and there are four species of sparrow hawks, one of them not much larger than a finch.

It is probably the smallest bird of prey, and there is no doubt that one species of West Indian humming bird is the smallest bird on earth, the _Vervain colibri_, of Jamaica, that hides its nest under an orange leaf, and, though an insect-eater, could be easily overpowered by an able-bodied bumblebee. In beauty some of the south Cuban species rival those of the Amazon Valley, and frequent every flowering shrub from the jungles of the coast lands to the highland meadows of the Sierra Maestra. In Hayti there are parklike plateaus where they often appear in swarms at a time of the year when the forests of the foothills are drenched by the afternoon cloudbursts of the rainy season, and on some of the smaller Antilles they are seen only during the flowering period of special plants.

In the solitudes of the Morne Range (San Domingo) mountain ravens rear their brood in the crevices of steep rocks, and fiercely attack birds of prey, not excepting the black-crested eagle, that now and then visits the sierras in quest of conies. But the winged constables of the highlands rarely leave their mountain reservation. Of Abd-el-Wahab, the Arabian heretic, it used to be said that "Mohammedan zealots shrank in affright from his superior fanaticism," and on the midway terraces of the Dominican sierras the persecution mania of the giant crow yields to that of the great shrike, the _Lanius rufus_, that operates pairwise and assails all winged comers with absolutely reckless courage.

The raven of the Mornes seems to be identical with the cosmopolitan forager that is found in the uplands of the eastern continent from the bleak summit regions of the Hindu-Kush to the sierras of Portugal, and from the Atlas to the Norwegian Alps; but there are several exclusively West Indian species of the genus _Corvus_, including a steel-blue rook that flits about the Cuban coffee plantations and has a curious habit of perching on a stump and talking to itself in a sort of croaking chuckle for half hours together.

The _gallinæ_, as might be expected from their limited wing-power, are well represented in the number of individuals, rather than of species. Turkeys, though abundant in the coast forests of Central America, are not found wild in any part of the West Indies, where the perennial presence of berries would be as inviting as the absence of foxes.

In the mountains some species of curassow have, however, developed into a stately game bird, the _Oreophasis niger_, or highland "pheasant," that lays a dozen large eggs, and in its courtship season becomes so infatuated that it can be approached and killed with a common walking-stick. The consequent persecution has made it rather scarce in famine-stricken Cuba, but in Hayti it can still be seen in troops of a dozen or more, scratching up the dry leaves of the sierra forests, or pecking at insect-haunted shrubs, exactly like a flock of Tennessee turkeys.

There are also several varieties of true pheasants, and two species of quail (besides the above-mentioned _codornilla_), and in eastern Cuba numerous barnyard chickens have taken to the woods and become so shy that it seems a puzzle how their ancestors in the coast range of Burmah could ever be captured and domesticated. They still practice polygamy, combined with a system of co-operative housekeeping, to judge from the number of eggs that are often found in one nest. At the approach of an unfeathered biped the hen bird takes wing with a screech, and is apt to vanish for the rest of that day. The roosters are rarely seen, their glaring colors having faded into more protective shades of olive and brown, but at dawn of day their shrill reveille can be heard from afar in the heart of the pathless jungle woods.

[_To be continued._]

INSANE CHARACTERS IN FICTION AND THE DRAMA.

BY PROF. CESARE LOMBROSO.

One of the things that most strikes one who compares the ancient theater, and even the theater of a few years ago, with the modern theater, is the enormous difference in the character of the personages, and particularly the curious frequency of insane as principal personages in the modern theater. We have come to such a point that one may be almost sure that in reading over a new play, by Ibsen, for example, he will find three or four insane personages in it, if, the characters are not all so. These madmen have characteristics so particularized as to seem as if they might have been depicted by an alienist. If the protagonists are not mad, they are agitated by such violent and strange passions as the ordinary world never meets in life; which it therefore refuses to accept when they are described in a scientific book, but nevertheless receives them when it sees them in the scenes or meets them in the romances of the great modern novelists.

Ibsen, for example, has made a most exact picture of the progressive general paralysis which arises, precisely as he depicts it, in men of genius, of great mental activity, who have wasted their hereditary power in pleasures or excessive work; and there is in them both impulsiveness and want of will power, complete perversion of all the instincts, and mental confusion, alternating here and there with genial flashes; but he is wrong in accumulating in a single subject the maladies of a large number of diseased, and therefore exaggerating their eccentricities--as he exaggerates atavism and heredity of disease when he makes the morbid son repeat the same incoherent phrases as the father from whom he inherits his disorder used.

Just and true, however, is that other form of heredity under which from a father corrupted by licentious indulgence and by alcohol, and criminally vicious, is born, besides a paresic son, a lascivious and criminal daughter, who throws herself into prostitution at the first opportunity without any special cause.