Page images
PDF
EPUB

breeds of oxen, sheep, and horses, we may discern additional examples of deviation from an original standard. Some breeds of sheep and oxen are destitute of horns; others, on the contrary, are distinguished by the large size of their horns. In Paraguay there are breeds of oxen without horns, descended from the common horned race. With respect to horses, Blumenbach again observes that there is less difference in the form of the skull in the most dissimilar of mankind, than between the elongated head of the Neapolitan horse and the skull of the Hungarian breed, which is remarkable for its shortness and the extent of the lower jaw. The varieties in the covering of animals are not less worthy of notice than those to which reference has already been made. In the same race of sheep, some are clothed with wool, others with hair. It is known that if a flock is neglected, the fine wool is succeeded by a much coarser growth, intermixed with strong hairs; the breed, being no longer kept up with care, seems gradually to degenerate towards the characters of the argali, or wild sheep of Siberia, which naturalists consider to be the stock whence all domestic sheep have proceeded. A striking specimen of the changes which occur in breeds is afforded by the sheep of the West India islands, which, although descended from the woolly sheep of Europe, are covered with coarse hair. The deterioration has usually been attributed to the heat of the climate; but it must also be referred to the circumstance of their breed having been neglected. Other animals, such as goats and dogs, display a similar variety in the nature of their covering.

The preceding facts clearly prove that, in the lower animal creation, there spring up, in the same species, varieties of an analogous or similar kind to those which mark the different races of men. The existence of this analogy confirms still further the opinion expressed as to the unity of the human species. It now only remains to inquire whether it is absolutely known that varieties have arisen in a family or race of men similar to those diversities which distinguish one nation from another.

It is a well-attested fact that, among negroes and other dark-coloured tribes, individuals of the albino and xanthous complexions are not unfrequently born; and with respect to form and structure, and the texture of the skin and hair, many instances are recorded wherein

surprising peculiarities have made their appearance in a race or family, and some in which these have been transmitted to descendants. The description of such cases would exceed the limits of the present treatise; but an account of several may be seen by referring to the author whom we already cited.

It appears, therefore, that if we apply to the subject under discussion the several criteria stated at the outset of this inquiry, the results, every one, lead to the inference that the various nations of the globe are descended from the same stock. This inference is drawn, first, from the observed uniformity in the grand laws of their animal economy, allowance, of course, being made for the effects of climate and of particular habits; secondly, from the existence in the same species among the inferior tribes of the creation, of varieties analogous to those which occur in mankind; and thirdly, from the fact of varieties being really known to have sprung up among men, more or less similar to those which distinguish different nations. There is, nevertheless, a point at which the similarity between the two cases obviously terminates: the peculiarities which arose in the human species at a remote and unknown period have become the characteristic marks of large nations, whereas those which have made their appearance in later times, have, in general, extended very little beyond the individuals in whom they first showed themselves, and certainly have never attained to anything like a prevalence throughout whole communities. this is a circumstance which it does not seem difficult to explain, if we consider that, ever since the population of the world has been of large amount, the possessors of any peculiar organisation have borne such a very small numerical proportion to the nation to which they belonged, that it is no way surprising that they should soon have been lost in the general mass, still less that they should have failed to impress it with their own peculiar characters. In the early period of the world, when mankind, few in numbers, were beginning to disperse themselves in detached bodies over the face of the earth, the case was altogether different, and we can easily understand how, if any varieties of colour, form, or structure, then originated in the human

But

• Dr. Prichard's "Researches into the Physical History of Mankind."

race, they would naturally, as society multiplied, become the characteristics of a whole nation. These considerations may suggest to us the manner in which national diversities first obtained their ascendancy. The causes of those diversities are, and probably ever will remain, enveloped in mystery; and the inference as to the unity of the human kind is not weakened by our inability to assign those causes, since we are ignorant of the occasions even of the varieties which sometimes display themselves within the limits of a single family.

It will be seen, however, upon a comprehensive survey, that in the distribution of the different races of men there is a certain relation to climates. We may observe that the black races of men are principally situated within the torrid zone; and the white races in the regions approaching towards the pole; and that the countries bordering on the torrid zone are generally inhabited by nations of a middle complexion. It further appears that the natives of mountainous and elevated tracts are usually of lighter colour than the natives of the low and hot plains on the sea-coast. In Africa, most of the races between the tropics are either black or of a very deep colour; while beyond the tropics the prevailing complexion is either brown or red. The people of Fezzan, who are of a black hue, form an exception to this rule; but it has been remarked of them, that they are chiefly slave-dealers, and have been intermixed with the negro race brought from the interior of Africa. In other countries of the globe, the majority of the nations near the equator are almost black. In India there are black tribes in Malabar; and the Hindoos of the Deccan are generally very dark, as are also the inhabitants of Ceylon. In most of the islands of the Indian ocean, the aborigines are of a black colour; and still further eastward are the Papuas of New Guinea and the black inhabitants of Solomon's islands and the New Hebrides. In equatorial America, the natives are not so dark as in other parts of the torrid zone; but its elevated mountains, vast rivers, and extensive forests, impart a peculiar character to the climate of the New World, which may probably account for the difference. In the low countries of California it is remarked that the population are nearly as dark as negroes.

It is a very general opinion, that the

origin of the diversities of colour in mankind is to be referred entirely to the gradual influence of climate and of the sun's rays in darkening the complexion; it being a commonly-observed fact, that the skin, even of white men, becomes embrowned by constant exposure to the heat. But there are circumstances which militate against this opinion. There is positive testimony that the offspring of individuals, darkened by the sun in hot countries, is born with the original complexion, and not with the acquired hue of the parents; besides which, it is known that white races of men, who have been removed from a cold to a hot climate, and have not intermarried with the natives, have retained for ages their original colour; while, on the other hand, black families, when transplanted into more temperate coun tries, have remained for generations of exactly the same hue as their African progenitors. Dr. Prichard has also remarked that the above supposition is contrary to a general law of the animal economy, according to which, acquired varieties are not transmitted from parents to their offspring, but terminate in the generation in which they have had their origin.

Yet although it seems that the existence of varieties cannot be attributed to the slow and gradual operation of climate upon successive generations, numerous facts lead to the conclusion that there is a natural tendency among races, both of men and animals, to the production of varieties suited in form and constitution to the local circumstances of the country where they arise. Or it may, perhaps, be better explained, in some cases, by supposing that, whatever varieties occur, the ability to establish a footing in any country belongs to those only which possess a constitution adapted to local circumstances. Thus men of the xanthous variety of colour are known to spring up among the negroes in Africa; but their constitution being entirely unsuited to the climate, we cannot believe that they would ever become numerous in that continent. In the temperately-cold regions of the world they would be favourably circumstanced; and we accordingly see that this variety has multiplied there to a considerable extent.

Dr. Prichard's "Researches," vol. it. pp. 532. &e. Acquired varieties are opposed to those which a person brings into the world at his birth.

1100 parts is, or how that unit is represented on our scale, provided that we apply the same unit and measure to all the three sides of the triangle. Thus it is of no consequence whether the 1100 parts of the hypotenuse be 1100 miles, or yards, or feet, &c. or whether an inch, or half an inch, &c. on our scale represent a mile, provided that in taking all the three measures the inch or half inch represents the same quantity: if half an inch, for instance, represent 100 miles when we measure AB, it must represent the same quantity of miles when we measure B C or A C.

(9.) In order, therefore, to resolve a triangle by construction, it is only necessary to have the means of constructing the data, that is, the things given, and then we measure the lines or angles that are unknown: for if the data be sufficient, the very act itself of representing them on paper enables us also to represent those lines and angles that are not given, and when those unknown quantities are represented on paper, and on a scale proportional to the known quantities, we have but to measure them and their values are then ascertained. The examples, which it will be necessary to subjoin in this Part, of this mode of resolving triangles, will sufficiently illustrate the above explanation of the phrase resolving a case by construction.

CHAPTER II.

Preliminary Considerations.- On Tra

verses.

(10.) IF we often interrupted the course of useful pursuits to analyze the manner in which we perform some of the complex though common operations of life, a very small part only of that which is actually accomplished by human energies and industry would then be achieved: yet there are cases in which, in order to obtain a clear conception of matters of science or art, with which we are not familiar, it is expedient to advert to those every day occupations, which have some connexion more or less remote with the object of inquiry, and to consider the different processes, which lead to their completion, and which, generally, through the influence of habit, make no impression on our minds,

Thus the very common operation of walking from any one spot to another, not in sight at the commencement of our journey, is connected with the infinitely

more difficult one of directing the course of a ship through the ocean. The traveller on land has, in common with the mariner, to ascertain his course and distance: but the great point, in which journeying upon land and sailing on the sea differ in this respect, is, that on land the course and distance are usually determined by means of fixed marks on the surface of the earth, with the appearance of which the traveller is either acquainted, or is enabled to avail himself of their assistance by the aid of certain general considerations drawn from experience; which is indeed the source of the greater part of that more humble knowledge which all mankind possess in common. In traversing the ocean, on which vessels leave no permanent trace behind them of the path they have pursued, and the same difficulties present themselves to each succeeding voyager, the sky and the sea alone remain to direct the mariner in his course.

It is easy, however, to imagine a case in which the traveller on land may be wholly dependent on those guides, which a knowledge of some of the first principles of navigation alone can furnish.

(11.) Thus (fig. 2) we will suppose

A

Fig. 2

him at a house A situated on some extensive and barren plain, on which there is no object that can by possibility serve

as a landmark to direct his steps, and that he wishes to traverse the plain to a village B at the distance of sixty nautical (Art. 44) miles from the spot on which the house is placed: let a line AC be conceived to be drawn through that spot towards the North Pole, or North point of the heavens; and let a line AB join the house and the village; and let the direction of the village from the house, or the line A B, make an angle of 45° with the line A C, that is, let the angle BAC equal 45°: draw also the line BC at right angles to A C. The angle BAC and the distance B A (=60 nautical miles) are determined, by means which will be explained hereafter, (Art. 54.)

Let us further suppose that the most eastern point of a large body of water, shown in fig. 2 by the irregular and crooked line, is situated due North of the house A, and 'that the situation and extent of this lake obliges our traveller, in his journey from A to B, to pursue the track marked out by the dotted line. Such a track is called by seamen a traverse; and it will be readily seen, that none of the ordinary modes which are in daily practice, of finding the way from one spot to another, will avail a person so circumstanced as in our example. (12.) Before, however, we proceed to explain all the contrivances which are to be substituted for such ordinary modes, we shall define certain terms which it will be convenient to make use of hereafter; we shall also give a more simple example than that proposed in

the last article.

Few of our readers can be ignorant, that such lines as B C and A B in fig. 2, supposed to be drawn on the round surface of the earth, cannot be straight lines;-they must be curved lines. But as the earth is a globe of very large dimensions, (Art. 44,) a very small curved distance, such as sixty miles, differs very slightly from a straight line; and therefore in our investigations we may assume the line A B, and of course all the other lines in the figure smaller than A B, to be straight lines. We shall find hereafter, (Art. 52,) that no error can possibly arise from this supposi tion in questions similar to those solved in examples I. and II.; and such an assumption, it is evident, must materially facilitate our inquiries. Draw the right angled triangles a b D, bc B. We shall call the line A C, drawn towards the north pole, and all lines

parallel to it, as a b, meridian lines; and as those lines are drawn towards the top of our page, that top will represent the north, the right of the paper the east, the left the west, and the bottom the south. This supposition is invariably made with respect to all figures drawn to illustrate problems in navigation, so that we are enabled to discover the nature of lines by the position in which we find them, with reference to the top of the page. We perceive that the lines AB, D b, b B all make certain angles with meridian lines; these angles are called courses; the angle CAB is called the course from A to B; and as it equals 45°, the course from A to B is said to be N* 45° W, or 45° from the north, on the side of the west; and as this is just half way between the two, it is NW. The course from one place to another is also called the bearing of the latter place from the former; thus B is said to bear N 45° W from A, and A, S 45° E from B. For the present we shall call all lines drawn at right angles to meridian lines, departures. Thus B C, a D, and Bc are termed departures; also the lines which make with the meridian lines the angles called courses are called nautical distances ; such are the lines A B, D b, and b B. The true nature of courses, departures, and nautical distances, will be better understood hereafter, (Art. 51 and 52.)

EXAMPLE I.

to travel, or a ship be supposed to sail, (13.) Let a man (fig. 1) be supposed eleven miles, (from B to A); let the course (A B C) make an angle of 53° with the meridian line (B C); and let it be required to find the length of the line BC, or, in other words, the distance made good in the direction B C, or from north towards the south.

is compounded of a southern and westIt is plain, that as the ship's motion ern course, she must sail farther than the length of the line BC before she makes good that distance towards the south; we see, in fact, that she sails on the hypotenuse of the triangle instead is by the last article S 53° W. of the perpendicular. The course also

Draw the line B A proportional to eleven miles, making an angle of 53° with another line B C drawn from the

It seems scarcely necessary to mention, that the letters N, S, E, and W stand for north, south, east, and west respectively. The letter b stands for by: thus, north by west is written Nb W.,

1100 parts is, or how that unit is represented on our scale, provided that we apply the same unit and measure to all the three sides of the triangle. Thus it is of no consequence whether the 1100 parts of the hypotenuse be 1100 miles, or yards, or feet, &c. or whether an inch, or half an inch, &c. on our scale represent a mile, provided that in taking all the three measures the inch or half inch represents the same quantity: if half an inch, for instance, represent 100 miles when we measure AB, it must represent the same quantity of miles when we measure B C or A C.

(9.) In order, therefore, to resolve a triangle by construction, it is only necessary to have the means of constructing the data, that is, the things given, and then we measure the lines or angles that are unknown: for if the data be sufficient, the very act itself of representing them on paper enables us also to represent those lines and angles that are not given, and when those unknown quantities are represented on paper, and on a scale proportional to the known quantities, we have but to measure them and their values are then ascertained. The examples, which it will be necessary to subjoin in this Part, of this mode of resolving triangles, will sufficiently illustrate the above explanation of the phrase resolving a case by construction.

CHAPTER II.

Preliminary Considerations.— On Tra

verses.

(10.) IF we often interrupted the course of useful pursuits to analyze the manner in which we perform some of the complex though common operations of life, a very small part only of that which is actually accomplished by human energies and industry would then be achieved: yet there are cases in which, in order to obtain a clear conception of matters of science or art, with which we are not familiar, it is expedient to advert to those every day occupations, which have some connexion more or less remote with the object of inquiry, and to consider the different processes, which lead to their completion, and which, generally, through the influence of habit, make no impression on our minds,

Thus the very common operation of walking from any one spot to another, not in sight at the commencement of our journey, is connected with the infinitely

more difficult one of directing the course of a ship through the ocean. The traveller on land has, in common with the mariner, to ascertain his course and distance: but the great point, in which journeying upon land and sailing on the sea differ in this respect, is, that on land the course and distance are usually determined by means of fixed marks on the surface of the earth, with the appearance of which the traveller is either acquainted, or is enabled to avail himself of their assistance by the aid of certain general considerations drawn from experience; which is indeed the source of the greater part of that more humble knowledge which all mankind possess in common. In traversing the ocean, on which vessels leave no permanent trace behind them of the path they have pursued, and the same difficulties present themselves to each succeeding voyager, the sky and the sea alone remain to direct the mariner in his course.

It is easy, however, to imagine a case in which the traveller on land may be wholly dependent on those guides, which a knowledge of some of the first principles of navigation alone can furnish.

(11.) Thus (fig. 2) we will suppose

A

Fig. 2

him at a house A situated on some extensive and barren plain, on which there is no object that can by possibility serve

« PreviousContinue »