Part 12

Hard on the heels of this work came news of Galvani's remarkable discovery (1790) of the fact that freshly amputated frogs' legs, on being touched along the lines of the muscles by dissimilar metals, were powerfully agitated. We can only speak of this discovery as the stumbling on to an isolated fact, for it was reserved for Volta to establish the generalization that a current is produced in the conductor joining dissimilar metals when the latter are both in contact with a suitable electrolyte (or liquid capable both of conducting electricity and of acting on one, and incidentally also sometimes both, of the metals). Meantime (Du Bois-Reymond observes), "wherever frogs were to be found, and where two different kinds of metal could be procured, everybody was anxious to see the mangled limbs of frogs brought to life in this wonderful way. Physiologists believed that at last they should realize their visions of a vital power, and physicians that no cure was impossible."

Volta first discovered merely the fact of electrification by contact. He wrote to Galvani: "I don't need your frog. Give me two metals and a moist rag, and I will produce your animal electricity. Your frog is nothing but a moist conductor, and in this respect it is inferior to my wet rag!" Nobili, nevertheless, in 1825 proved the existence of galvanic currents in muscles.

Later on Volta invented the "_couronne des tasses_" (crown of cups), thus at the same time adopting the general form of cell used, with modifications, to-day, and producing the higher electromotive force, or electrical pressure, consequent on the multiplication of the cells in a series battery.

Just before Volta's celebrated communication to the Royal Society, in 1800, Fabroni, of Florence, in discussing Galvani's phenomenon, went to the root of the matter by suggesting that the energy of chemical action was at the bottom of galvanic manifestations, and he was warmly upheld in this contention by Sir Humphry Davy, who, upon the publication of Volta's discoveries, constructed a most elaborate battery with which (apparently about 1806) he produced the arc light between carbon pencils.

In the year referred to, Davy published the results of a series of experiments of enormous significance, among other things of the isolation of the alkali metals, sodium and potassium, whose existence had hitherto not been dreamed of. The simple electrolytic decomposition of water had been accomplished by Nicolson and Carlisle in the last year of the eighteenth century. Sir W. S. Harris says: "A series of new substances was speedily discovered, the existence of which had never before been imagined. Oxygen, chlorine, and acids were all dragged, as it were, to the positive pole, while metals, inflammable bodies, alkalies, and earths became determined to the negative pole of the battery. When wires connected with each extremity of the new battery were tipped with prepared and well-pointed charcoal, and the points brought near each other, then a most intense and pure evolution of light followed, which on separating the points extended to a gorgeous arc." It was at first supposed that the galvanic or voltaic electricity was distinct from the so-called "frictional" or "ordinary" electricity.

A distinguished contemporary of Cavendish was Coulomb, the value of whose work in developing certain exceedingly important mathematical laws with regard to action at a distance, surface densities, and rates of charge dissipation can hardly be overestimated. His name was given to the torsion balance which, since his day, has been the standard instrument for measuring electric and magnetic attractions and repulsions. The importance of his work has since been recognized by the perpetuation of his name in connection with the unit of quantity of electricity, as that of Volta has been honored by its use, abbreviated (volt), to designate the unit of electrical tension or pressure.

Certain highly instructive and interesting data were accumulated about this time by Volta, Laplace, Saussure, and the renowned chemist Lavoisier, in connection with the subject of electrification produced when evaporation, and the liberation of gases and vapors in general from any cause, occurs. The liquid, solid, or mixture liberating the gas was contained in a metallic dish and the resultant electrification of the latter examined qualitatively. Volta's observations led him to conclude that the electrification was always negative, but Saussure demonstrated finally that its sign was dependent on the material of the dish. These experimenters covered, between them all, a somewhat extensive field, examining, among other things, the electrification resulting from the ebullition of various liquids, from the ordinary combustion of fuel, and from the decomposition of acids by metals to liberate hydrogen.

About the end of the first decade of the century Poisson attacked the phenomena of electricity analytically, and succeeded in demonstrating the right of electrical investigation to rank among the exact sciences. Of his most important mathematical propositions is one in which, assuming as a working hypothesis the existence of two mutually attracting fluids, he deduced formulæ covering the distribution of these fluids on the surfaces of two conducting spheres, in or out of contact.

A great deal of work was done during the end of the last century and the beginning of the present one on what is now known as pyro-electrification. The Abbé Haüy discovered that fragments of tourmaline crystal exhibited opposite electrifications on opposite extremities of their lines of cleavage. It is this crystal also which has unusually remarkable powers of polarizing light, and which, under electro-magnetic stress, suffers modifications of the latter property. Haüy investigated the field with much diligence, and succeeded in cataloguing a large number of natural crystals by the side of tourmaline. The subject was amplified later by Sir David Brewster, who added a series of artificial crystalline salts to the list of pyro-electrical materials, among them, notably, hydro-potassic (and sodic) tartrate. The property was found not always to reside on these substances, but to be developed by heating them. Brewster found that even powdered tourmaline exhibited opposite electrifications on the opposite extremities of each tiny particle, causing the latter to act, so far as attractions and repulsions went, as infinitesimal magnets.

Our rapid and imperfect survey has now brought us to the threshold of the great activity in electrical work elicited by the tremendous discovery, made by Professor Oersted, of Copenhagen, of the existence of the electro-magnetic field. It happens that two of the most amiable and estimable individuals that have ever devoted their lives to scientific research stand out in this connection head and shoulders above all other investigators--Ampère and Faraday, the latter sixteen years younger than the former and destined to long survive him.

WINGLESS BIRDS.

BY PHILIPPE GLANGEAUD.

It is often said that there are no rules without exceptions. We purpose to test the truth of this maxim once more. Fishes are made to live in water, but some of them pass the greater part of their existence in mud. Some even perch upon trees, thus competing with birds, whose kingdom is the air, and which are able, with the aid of their wings, to plunge into space and travel rapidly over considerable distances. Yet there are birds, deprived by Nature, which do not possess the wing characteristic of the feathered tribe, and are consequently, like the majority of animals, pinned to the soil.

Birds do not all have equal power of flight, which is closely related to the extent of the development of their wings. There exist all grades in the spread of wings between that of the condor, which is four times the length of the body, whereby the bird is able to rise to the height of nearly twenty-five thousand feet, and the little winglets of the auk, which are of no use to it. The penguins have still smaller wings, which are nothing more than short, flattened stumps, without proper feathers and covered with a fine, hairlike down which might be taken for scales.

Another group of birds exists, called appropriately _Brevipennes_, the wings of which are so poorly developed as to be wholly unsuitable for flight. As an offset and just compensation for this, their long and robust legs permit them to run with extraordinary speed. For that reason they have been called running birds, in distinction from other kinds that constitute the group of flying birds. Among them are some gigantic birds, and also some that have no visible wings on the outside of their bodies, and may therefore be properly called wingless.

The ostrich is a member of this group. With its bare, callous head and short bill, its long, featherless neck, and its massive body, supported by long, half-bare legs, ending in two large toes; its very short wings, formed of soft and flexible feathers; and its plume-shaped tail, it presents a very special appearance among the birds.

The nandous, the American representatives of the ostrich, have still shorter wings, which have no _remigia_ at all, and terminate in a horny appendage, and they have no tail feathers.

The cassowary and the emu also resemble the ostrich in many points, but their wings are still more reduced than those of the nandou. They are only slightly distinct, and can not be seen when the bird holds them close up to its body. In the _Apteryx_, the name of which, from the Greek, means without wings, the organs of flight are hardly apparent, and consist simply of a very short stump bearing a thick and hooked nail. The _Apteryx_, which is also called _Kiwi_, a native of New Zealand, is the most singular of living birds. The neck and the body are continuous, and the moderately sized head is furnished with a long beak resembling that of the ibis. Having long hairs similar to the mustaches of cats at its base, it is different from the bills of all other existing birds in possessing nostrils that open at its upper point. Although the _Apteryx_ can not fly, it runs very fast, despite the shortness of its legs, and can defend itself very effectively against assailants by the aid of its long-nailed and sharp-nailed feet. The tail is absent like the wings. The very pliant feathers are extremely curious, of the shape of a lance-head, pendent, loose, silky, with jagged barbs, and increase in length as they go back from the neck. The bird is of the size of a fowl, and when in its normal position stands with its body almost vertical, and carries the suggestion of a caricature--resembling, we might say, a feathered sack, with only a long-billed head and the claws projecting, and one beholding it feels that he is looking at some unfinished creature. It is a nocturnal bird, of fierce temper, and has become rare in consequence of the merciless war that is made upon it. Everything is strange about it, even the single egg it lays, which weighs about a quarter as much as its body.

Together with the _Apteryx_, there lived in New Zealand a bird that reached the height of nearly twelve feet--the _Dinornis_. It and the _Phororhaces_ and the _Brontornis_, which have been recently exhumed in Patagonia, might be regarded as the giants of birds. This bird was known to the natives as the _Moa_, and lived in troops like the ostriches. Its organization was very much like that of the _Apteryx_, from which it was, however, distinguished by its great size, long neck, and short beak. It seems to have had the aspect of an ostrich, with a feathered neck and no wings or tail. The feet of the _Dinornis_, with their three large toes, were really enormous. Isolated fragments of its bones suggest very large mammals, rather than birds. The femur and tibia are larger than those of a bear, the tibia alone being about four feet long, and the thickness, in the narrowest part, of the width of a man's hand, while it was more than seven inches in the thickest part. The sternum, on the other hand, was small, convex, and longer than broad. The wing could not have been visible on the outside of the body, for the bones that constitute them are proportionally smaller than those of the _Apteryx_. There was, therefore, a maximum reduction of the wing in this bird.

The _Dinornis_ was covered with a rich plumage, and this was doubtless what led to its destruction, women preferring its plumes to all other ornaments. The large number of bones which have been discovered in the alluviums, the caves, and the peat bogs of New Zealand authorize the thought that the island was once inhabited by a considerable number of these birds, which were able easily to repel the attacks of other animals by means of their big feet. But they could stand no chance against Nature's more terrible destroyer--man--who, when seeking the gratification of his taste and fancy, does not hesitate to exterminate whole species. The natives of New Zealand still recall the history of these singular birds; their extermination seems to have occurred about the time the island was visited by Captain Cook (1767-1778). Moreover, some of the bones collected in later years still had animal matter upon them. Even parts of the windpipe have been discovered, mixed with charcoal, and evidences of cooking have been found.

A near relative of the _Dinornis_, which the Maoris regard as extinct, is the _Notornis_, of which only four living specimens have been found since 1842, the last one having been captured in the latter part of 1898.

The eggs of the _Dinornis_ were very large, having a capacity of about a gallon and being equivalent to eighty hen's eggs. Still larger eggs than these, however, are known. In 1851 Isidore Geoffroy Saint-Hilaire exhibited, in the French Academy of Sciences, eggs of a bird coming from Madagascar that had a capacity of two gallons. Some specimens of these eggs may be seen in the galleries of the Paris Museum, and still larger eggs have been found. The museum in London has one with a capacity exceeding eleven quarts, or equivalent to two hundred and twenty hen's eggs, or more than seventy thousand humming birds' eggs. It was thought at first that the bird which laid these gigantic eggs was still living, for natives of Madagascar spoke of having seen a bird of colossal size that could throw down an ox and make a meal of it. Such, however, were not the ways of the bird called the _Epiornis_, which had no talons or wings, and fed on vegetable substances. The description by the celebrated traveler Marco Polo of a great flying bird of prey, called a roc, has no reference to the _Epiornis_. M. Grandidier has demonstrated that this bird no longer exists in Madagascar, and that if man ever knew it the stories with marvelous details which the savages hand down from generation to generation make no mention of it. We owe to M. Grandidier, M. Milne-Edwards, and Major Forsyth what is known of the history of this large wingless bird, which resembles the _Dinornis_ in several points. If its size was proportioned to that of its eggs it should have been twice as large as the _Dinornis_. It was not, however, but constituted a family represented by very diverse forms and of variable size, though never much exceeding eleven feet. The head was similar in appearance to that of the _Dinornis_, but the surface of the forehead was furrowed with wrinkles and cavities, indicating the presence of a crest of large feathers. A curious peculiarity was the opening of the Eustachian tube directly on the exterior. The cervical vertebræ are very numerous, while the sternum is much reduced. It is a flat bone, broad but very short, especially in the median part. The wing also has suffered a great regression, for it comprises only a thin, short rod, the humerus, and a small osseous mass representing all the other bones of the wing stuck together. The _Epiornis_ had no wings externally visible. The bones of the feet were, on the other hand, of considerable size, and indicate that the bird that possessed them was larger than the _Dinornis_.

The _Epiornis_, according to M. Milne-Edwards, frequented the borders of waters, keeping among the reeds along lakes and rivers, for its bones are found associated with those of turtles, crocodiles, and a small hippopotamus. It most probably nested in the low plains around lakes.

Just as the _Apteryx_ among birds, and the bison and the beaver among mammals, so the _Dinornis_ and the _Epiornis_ have been destroyed as man has extended his abode and his domination.

When we regard the fauna of Madagascar and of New Zealand we are struck by the great resemblance between them, from the points of view of their recent and ancient vertebrate fauna. These resemblances suggest the past existence of relations between these two lands now separated by a wide expanse of sea, and this agrees with geological observations.--_Translated for the Popular Science Monthly from La Nature._

SKETCH OF FREDERICK C. SELOUS.

The description of Selous, in Men and Women of the Time, as "explorer, naturalist, and sportsman," is suggestive of the manner in which his career has been developed and his fame has grown. Beginning his active life as a mere hunter of big game in the wilds of South Africa, and known at first only as a sportsman, he has become recognized as one of the leading, most intelligent, and most efficient explorers of his time, and is accepted as the most eminent authority respecting what relates to the large and important region of Mashonaland.

FREDERICK COURTENAY SELOUS was born in London, the son of a father of Huguenot extraction and of a mother who, descended from the Bruces of Clackmannan, could count Robert Bruce among her ancestors, and was also related to Bruce, the Abyssinian traveler. He was taught at Bruce Castle, Tottenham, and then went to school at Rugby, where he distinguished himself by his activity, which was displayed in his high spirits and love of violent mischief and by his personal courage to such an extent that his schoolfellows wittily nicknamed him "Zealous."

Leaving Rugby when sixteen or seventeen years old, he spent two years in Switzerland and Germany, studying at Neufchâtel and Wiesbaden. His hardy activity seems to have been as marked in Germany as at Rugby, for it is recorded of him that he attracted some notice in the papers by jumping into the Rhine in winter after a wild duck which he had shot. He was not dressed for a swim, and, his great coat and top boots becoming filled with water, he had much difficulty in getting to shore with his game. His determination to achieve a career in South Africa by hunting and collecting specimens was apparently reached while he was still a youth, and at nineteen years of age he sailed from England, to land at Algoa Bay in 1871. Hunting was his object, as is substantially confessed in the title of his first book, A Hunter's Wanderings in Africa. The book won instant recognition as a story of sport and a hunter's prowess, and was regarded in that light by the critics and the general public. The Royal Geographical Society, however, perceived other qualities in the story he had to tell, and gave him successively honorable mention, the Cuthbert Peake grant, and, in 1883, the Founder's Gold Medal, the highest honor it had to bestow.

Among the earliest testimonials paid by this society to the value, as yet not generally appreciated, of Selous's work was that given by Lord Aberdare, president, in his anniversary address, delivered in May, 1881, to the services rendered to geography in the regions west of Lake Nyassa by Mr. Selous, who had "hitherto been known as a mighty hunter of large game.... This gentleman, we learn, in 1878 penetrated for one hundred and fifty miles the unknown country north of the Zambezi, in the direction of Lake Bangweolo. He has since crossed in various directions the Matabele country south of the Zambezi, discovering two new rivers and defining the course of others which had previously been laid down from vague information." Selous's Notes on the Chobi, it appears, had already been published by the Geographical Society.

Mr. Selous has spent most of his time since he began his African wanderings in 1871, except for occasional visits to England, in traveling and hunting over that part of the African continent with which his name as an explorer is associated. In 1877 he and some companions penetrated into Matabeleland to hunt elephants. Relating the story of his wanderings in an address to the Royal Geographical Society in 1893, he described his experiences with fever and ague, the attacks of which began in Griqualand in 1872, but came on only when he halted anywhere a few days. North of the Zambezi he made several journeys among the Balongas, and spent a wretched rainy season, almost without equipment, on the Manica table-land, of the luxuriant vegetation of which, with sweet-smelling flowers after the rains, he gave a glowing description in his address. Interesting observations were made on some of the northern rivers. The curious phenomena of the steady rise of the waters of the Chobi and Machabi--an outlet of the Okavango--was observed from the first week in June till the last week in September, when the flood began to recede.

From 1882 the journeys acquired additional geographical importance, and Mr. Selous proceeded to rectify the maps of Mashonaland made by earlier travelers, taking constant compass bearings, sketching the courses of rivers, and fixing the positions of tributaries. The value of this work was made manifest in a magnificent large scale map of the country.

This map, which was published in 1895, was intended, first and chiefly, to illustrate the work done by Mr. Selous while in the service of the South African Company; and, secondly, to embody, as far as possible, the knowledge possessed of the entire region extending from Fort Salisbury to the northward as far as the Zambezi, and to the eastward as far as the lower Pungwe. Mr. Selous's manuscript originals, deposited in the map room of the Royal Geographical Society, comprise a compass survey, showing the routes during a year's employment in the service of the British South African Company, September 1, 1890, to September, 1891, on a scale of 1:255,000; a sketch map, showing the route of the Manika Mission from Fort Charter to Umtassa's and thence to the camp near Mount Wedza, and also the routes taken by Mr. Selous from the camp near Mount Wedza to Makoni's, Mangwendi's, Maranka's, and back to Makoni's, on a scale of 1:255,000; a sketch of routes from Umtali to Mapanda (Pungwe) and back, in 1891, on the same scale; a sketch of Mashonaland, showing tribal boundaries, on the same scale; a rough survey map of the countries ruled over by the Makorikori chiefs, for which a mineral concession had been granted to the Selous Exploration Syndicate, on a scale of 1:210,000; and about thirty sheets of manuscript maps and rounds of angles, utilized in the compilation of the first four maps of this list.