The Macedonian Expeditions under Alexander the Great, the downfal of the Persian Empire, the beginning of intercourse with Western India, and the influence of the 116 years' duration of the Greco-Bactrian kingdom, mark one of the most important epochs of General History; or of that part of the progressive development of the History of the Human Race, which treats of the more intimate communication and union of the European countries of the West with South-Western Asia, the Valley of the Nile and Lybia. The sphere of the development of community of life, or of the common action and mutual influence of different nations, was not only immensely enlarged in material space, but it was also powerfully strengthened, and its moral grandeur increased, by the constant tendency of the unceasing efforts of the conqueror towards a blending of all the different races, and the formation of a general unity, under the animating influences of the Grecian spirit. The foundation of so many new cities at points the selection of which indicates higher and more general aims, the formation and arrangement of an independent community for the government of those cities, the tenderness of treatment towards national usages and native worship, all testify that the plan for a great organic whole was laid. At a later period, as is always the case, much which may not have been originally comprehended in the plan, developed itself from the nature of the relations established.

It has often been said, that if delight in nature were not altogether unknown to the ancients, yet that its expression was more rare and less animated among them than in modern times. Schiller, in his considerations on naïve and sentimental poetry, remarks, that “when we think of the glorious scenery which surrounded the ancient Greeks, and remember the free and constant intercourse with nature in which their happier skies enabled them to live, as well as how much more accordant their manners, their habits of feeling, and their modes of representation, were with the simplicity of nature, of which their poetic works convey so true an impress, we cannot but remark with surprise how few traces we find amongst them of the sentimental interest with which we moderns attach ourselves to natural scenes and objects. In the description of these, the Greek is indeed in the highest degree exact, faithful, and circumstantial, but without exhibiting more warmth of sympathy than in treating of a garment, a shield, or of a suit of armour. Nature appears to interest his understanding rather than his feelings; he does not cling to her with intimate affection and sweet melancholy, as do the moderns.”

In attempting to recount the most distinctly marked periods and gradations of the development of cosmical contemplation, we have in the last section endeavoured to depict the epoch, in which one hemisphere of the globe first became known to the cultivated nations inhabiting the other. The epoch of the most extensive discoveries upon the surface of our planet was immediately succeeded by man's first taking possession of a considerable part of the celestial spaces by the telescope. The application of a newly formed organ, of an instrument of space-penetrating power, called forth a new world of ideas. Now began a brilliant age of astronomy and mathematics; and in the latter the long series of profound investigators, leading to the “all-transforming” Leonard Euler, the year of whose birth (1707) is so near the year of Jacob Bernouilli's death.

A few names may suffice to recal the giant strides with which the human mind advanced in the 17th century, less from any outward incitements than from its own independent energies, and especially in the development of mathematical thought. The laws that regulate the fall of bodies, and the planetary motions, were recognised; the pressure of the atmosphere, the propagation of light, and its refraction and polarisation, were investigated. Mathematico-physical science was created, and established on firm foundations.

After the dissolution of the great Macedonian Empire comprising territories in the three Continents, the germs which the uniting and combining system of the government of Alexander had deposited in a fruitful soil, began to develop themselves every where, although with much diversity of form. In proportion as the national exclusiveness of the Hellenic character of thought vanished, and its creative inspiring power was less strikingly characterised by depth and intensity, increasing progress was made in the knowledge of the connection of phenomena, by a more animated and more extensive intercourse between nations, as well as by a generalisation of the views of Nature based on argumentative considerations. In the Syrian kingdom, by the Attalidæ of Pergamos, and under the Seleucidæ and the Ptolemies, this progress was favoured and promoted every where and almost at the same time by distinguished sovereigns. Grecian Egypt enjoyed the advantage of political unity, as well as that of geographical position; the influx of the Red Sea through the Straits of Bab-el-Mandeb to Suez and Akaba, (occupying one of the SSE.-NNW. fissures, of which I have elsewhere spoken), bringing the traffic and intercourse of the Indian Ocean within a few miles of the coasts of the Mediterranean.

The kingdom of the Seleucidæ did not enjoy the advantages of sea traffic, which the distribution of land and water, and the configuration of the coast line, offered to that of the Lagidæ; and its stability was endangered by the divisions produced by the diversity of the nations of which the different Satrapies were composed.

As fresh and vivid descriptions of natural scenes and objects are suited to enhance a love for the study of nature, so also is landscape painting. Both shew to us the external world in all its rich variety of forms, and both are capable, in various degrees, according as they are more or less happily conceived, of linking together the outward and the inward world. It is the tendency to form such links which marks the last and highest aim of representative art; but the scientific object to which these pages are devoted, restricts them to a different point of view; and landscape painting can be here considered only as it brings before us the characteristic physiognomy of different positions of the earth's surface, as it increases the longing desire for distant voyages, and as, in a manner equally instructive and agreeable, it incites to fuller intercourse with nature in her freedom.

In classical antiquity, from the peculiar direction of the Greek and Roman mind, landscape painting, like the poetic description of scenery, could scarcely become an independent object of art: both were used only as auxiliaries. Employed in complete subordination to other objects, landscape painting long served merely as a background to historical composition, or as an accidental ornament in the decoration of painted walls.

The fifteenth century belongs to those rare epochs in the history of the world, in which all the efforts of the human mind are invested with a determinate and common character, and manifest an unswerving direction towards a single object. The unity of these endeavours, the success with which they were crowned, and the vigour and activity displayed by entire nations, give grandeur and enduring splendour to the age of Columbus, of Sebastian Cabot, and of Vasco de Gama. Intervening between two different stages of cultivation, the fifteenth century forms a transition epoch belonging at once to the middle ages and to the commencement of modern times. It is the epoch of the greatest discoveries in geographical space, comprising almost all degrees of latitude, and almost every gradation of elevation of the earth's surface. To the inhabitants of Europe it doubled the works of Creation, while at the same time it offered to the intellect new and powerful incitements to the improvement of the natural sciences in their physical and mathematical departments.

The world of objects, now as in Alexander's campaigns but with yet more preponderating power, presented to the combining mind the separate forms of sensible objects, and the concurrent action of animating powers or forces.

Principal epochs of the progressive development and extension of the idea of the Cosmos as an organic whole.

The history of the physical contemplation of the universe is the history of the recognition of nature as a whole; it is the recital of the endeavours of man to conceive and comprehend the concurrent action of natural forces on the earth and in the regions of space: it accordingly marks the epochs of progress in the generalisation of physical views. It is that part of the history of our world of thought which relates to objects perceived by the senses, to the form of conglomerated matter, and to the forces by which it is pervaded.

In the first portion of this work, in the section on the limitation and scientific treatment of a physical description of the universe, I have endeavoured to point out the true relation which the separate branches of natural knowledge bear to that description, and to shew that the science of the Cosmos derives from those separate studies only the materials for its scientific foundation. The history of the recognition or knowledge of the universe as a whole,—of which history I now propose to present the leading ideas, and which, for the sake of brevity, I here term sometimes the “history of the Cosmos,” and sometimes the “history of the physical contemplation of the universe,”—must not, therefore, be confounded with the “history of the natural sciences,” as it is given in several of our best elementary books of physics, or in those of the morphology of plants and animals.

To satisfy a curiosity that is naturally excited by any thing new, great or uncommon, I tried to obtain all the information I could, connected with the Telescopes I endeavour to describe. To gratify a similar feeling in others, more remote from my opportunities of looking on, I venture to publish an account of what I have seen.

As I am hardy enough to do so without any assistance from, or even the cognizance of the noble projector of those instruments, whose liberality in diffusing his knowledge and wish for its promotion, leave me no uneasiness on this point, so I do not expect to give that information which men of deep research or mathematically close enquiry would desire. There are some particulars which might, perhaps, be more enlarged upon with advantage, but it has been my aim to place before the general reader such an account as will make the manufacture of the Specula, and the mechanism of the Telescopes, as plainly understood as could be expected, without entering with too much tediousness into minute details. I have been as explicit as possible in the history of the compound three foot Speculum, knowing that individuals whose inclination would lead them to construct Specula on a large scale, without possessing the pecuniary advantages of Lord Rosse, will be naturally led to adopt a course the most manageable and economical, and one which does not appear to be the less certain of success.

The rapid sale of the First Edition, together with the many very favorable opinions expressed in reference to it by the Newspaper Press, leads the Author to hope that this work has been presented in an acceptable form. In the present edition he has therefore merely supplied a few trifling omissions which an unavoidable hurry in bringing out the former, occasioned.

In the account of the three-foot Speculum which Lord Rosse published in the Philosophical Transactions for 1840, he speaks of the possibility of one six feet in diameter being cast. It might at that time have been considered as little less than a chimera by those who were not sufficiently acquainted with the experiments that had been made in his Lordship's laboratory, and there were not wanting some who denied altogether the practicability of the design. Various reasons were given why the attempt should be a failure, and many calculations entered into to prove the little benefit to be derived even supposing a perfect casting were obtained—But fortunately others thought differently; the idea had no sooner occurred to Lord Rosse than he determined to put it to the test, and we may say, without flattery, that no absurdity was likely to occupy a mind like his. The attempt has been made, and the result is perfect success.

As yet we cannot say how far it may advance our knowledge of the celestial spheres, or help us to understand more fully the mechanism of the universe; but this at all events is certain, that be the advantage great or small, it is the last step that can be taken to enlarge our acquaintance with those distant bodies, and all that is ever likely to be brought before us will now be seen.

Lord Rosse having satisfied himself by experiments with lenses that the Refracting Telescope could not be much improved, turned his attention to Reflectors; and as the first object of experimenters had always been to increase the magnifying power and light by the construction of as large a mirror as possible, so was it to this point that his Lordship's attention was also directed.

Previous to his experiments, there had not been any instrument constructed, with the exception of Sir W. Herschell's, which had given an opportunity of sufficiently well enjoying the advantage of the Reflecting Telescope; and even of this it has been lately stated, that it possessed but little, if any, practical superiority over others of smaller size.

Since Newton manufactured his Specula until the present day, there have been several opinions both as to the metals to be employed in their construction, and the quantities in which they should be mixed—some have recommended various proportions of tin and copper; some have added arsenic; some silver; some antimony; and others, the three together—the general aim of all the operators being to increase the whiteness, and to diminish the porosity and brittleness of the compound; for the last named property has destroyed a much greater number of Specula than it has allowed to be completed—it is the “asses' bridge” over which few have been fortunate enough to travel.