the geological epochs during which the ancient plants flourished there; hence the existence of these plants in these regions may be conceived, without our having recourse to changes so considerable as those which would have depended on the variation or the important modification in the inclination of the ecliptic.

The light which the polar regions enjoyed in ancient geological epochs, during at least half the year,-light so much the more intense, because the solar rays then traversed masses of air extremely heated and transparent, in consequence of the complete solution of aqueous vapour,-was doubtless sufficient for the life of these ancient vegetables. Its brilliancy and intensity during this lapse of time, compensated then in some degree for its nearly total absence, and its entire want, at a certain period of the year.

This hypothesis is so much the more admissible, because we are completely ignorant if these arborescent ferns, these equisetaceæ, these lycopodiaceae, of the coal formation, required a large quantity of light, and because the larger quantity of the species analogous to these last actually live in the most shaded places. Besides, it is possible that it may have been the case with these plants, as it is with many which still flourish, that a too great brilliancy of light may have fatigued instead of being of advantage to them. Such are, for example, nearly all the species of the genus Mirabilis, and the Silene nocturna, whose flowers expand only after the setting of the sun, Alpine plants, those which live constantly in gloomy shady places, and which, in consequence of this and other circumstances, cannot be raised, and cannot be made to flourish in our gardens, are also a proof of this. There are besides so many degrees in this respect in the vegetable scale, that we may very well admit that the trees and plants may have been able to live, as we have already remarked, in places alternately illuminated by a brilliant light, or nearly totally deprived of its enlivening influence.

In fact, all plants are far from requiring a large quantity of light, and perhaps it is in this respect as in regard to the temperature which is necessary for them. The difficulty, however, does not exist relative to this last influence, since all the facts show that these polar regions had, at the epoch when these arborescent ferns, equisetaceæ, and lycopodiaceæ lived, a tempera

ture equal to that of intertropical countries, and sufficient to enable the large pachydermatous animals, of which we find such numerous remains, to fulfil all their conditions of existence.

Thus the presence, in the polar regions, of fossil plants, of which the analogues live only in the hottest countries of the earth, does not in any degree prove that there has been a change of the inclination of the ecliptic; for these plants could flourish under the influence of the elevated temperature, and of the light which these regions then enjoyed. Besides, we should only admit such a change, which would have caused so many others, with extreme reserve, and if forced by the evidence of facts. Such a necessity not existing, it should be sufficient for us to have been able to conceive these phenomena by the aid of induction and analogy, the only one which is available to us for seizing the facts belonging to periods when there was no human witness.-L'Institut, No. 88.

Account of the Founding of a New Grand Observatory for the Russian Empire, by the Imperial Academy of Sciences of St Petersburgh.*

It is a truth which can scarcely be denied, that the cultivation of the sciences, both in the department of physics and natural history, is greatly promoted by royal patronage. These sciences imperatively require establishments, the original found-ing and subsequent maintenance of which far exceeds the abilities of any private individuals. This remark is especially true -with regard to Astronomy, the history of which clearly demonstrates the intimate connexion which exists between its advance and the protection of princes; whilst it is further interesting to observe, that monarchs themselves have frequently taken an active share in the extension of this science.

It was when Ptolemy Philadelphus invited wise men from Greece to Alexandria, and with their help formed a school afterwards so celebrated, that in 250 a. c. we see the rise of the first establishment in which the heavens were studied for a

Saint-Petersbourg. From the Press of the Imperial Academy of

Sciences.

long series of years. It was in the portico of the Museum, which was placed close to the palace of the king, in the Bruchion, that Eratosthenes fixed his armillary spheres, by which to follow the motions of the stars. A hundred years later, the same apparatus was employed by Hipparchus, the greatest astronomer of antiquity; and by Ptolemy, 150 years after the Christian era. Hipparchus had fixed in the same place his celestial sphere, which exhibited a representation of the stars, arranged according to the discoveries which he had made. Here, too, was found the Alidade of this same philosopher, as also the Astrolabe of Ptolemy, and his parallel rulers. After a flourishing existence of 400 years, in which the basis of practical astronomy was established, the Observatory of Alexandria began to decline, and it is probable it was entirely destroyed at the time that the Arabian conquest overthrew all the scientific establishments of that country.

If the period which succeeded, of nearly a thousand years duration, until the revival of letters, was truly a dark age for the most of the sciences, this is, at the same time, less true of astronomy than of any other. The Arabian caliphs and the Mongul khans vied with each other in their application to the study of this science, and in endeavouring to promote it by the establishment of observatories. The caliph Almamoum founded one observatory at Damas and another at Bagdad; and, at a later period, there was another established at Bagdad by the Egyptian caliph Hakem. At the overthrow of the caliphat, in the thirteenth century, astronomy found protection with the victorious Monguls. Holagu-Ilekan, the grandson of Gengiskan, the conqueror of Mostazem, the last of the Abassides, was a zealous patron of this science. Nassireddin de Thous, the greatest astronomer of his time, then flourished in the East. He had been banished the court of the caliph Mostazem by a low cabal. The brother of Holagu, and his predecessor in the khanate, Mangu by name, had previously declared his intention of founding an observatory, and had instructed his brother Holagu, who acted as his general against the caliphate, to send him the illustrious astronomer, as soon as he had made himself master of Irak. Mangu did not survive to see the accomplishment of this event; but as soon as Holagu had terminated his campaigns,

in which he penetrated as far as Egypt, he announced himself the Protector of Science. Nassireddin resorted to his court, and the strictest friendship was forthwith established between the Khan and Kodjah. Immediately after the capture of Bagdad, in 1258, the khan gave orders to the treasurer to pay over to Nassireddin whatever sums he might demand for scientific objects; and the following year the foundation of the observatory in the capital, Meragah, was laid, about seventy miles from Tauris. The building was placed upon a hill in the neighbourhood of the town, and there Nassireddin made observations to a very advanced age; and the result of these labours is what is now known under the name of the Tables of Ilekan, which for a long time have been the most celebrated of the East. A description of this observatory of Meragah still exists, which was drawn up by Mujawad de Damas, the friend and assistant of Nassireddin; from which it appears that the establishment possessed four instruments of Grecian workmanship, and five of Arabian invention, all of such dimensions as to require very substantial buildings for their accommodation.

Previous to the revival of astronomy in Europe, it flourished amongst the Usbek Tartars, whose prince, Ulugh-Bey, grandson of Tamerlan, was beyond comparison the greatest astronomer of the Middle Ages. Ulugh-Bey reigned at the commencement of the fifteenth century, for forty years, and collected in Samarkand, his capital, the most able astronomers of Asia,-though, more learned than any of them, they acted merely as his assistants in his observatory. His instruments were magnificent, and of a prodigious size. Amongst others he had a gnomon 180 feet high, by means of which was determined, by the shadows, the latitude of Samarkand, and the obliquity of the ecliptic. The tables of Ulugh-Bey, and his catalogue of fixed stars, are very properly considered as the principal work on astronomy in the Middle Ages, and imply the taking of observations which surpass in accuracy all that had previously been made.

It is to these princes that astronomy owes its preservation of the knowledge acquired by the Greeks, not less than its extension, and its conveyance into Europe. As early as the thirteenth century, the Emperor Frederick the Second caused the

works of Ptolemy to be translated from Arabian into Greek, and Alphonso, King of Castile, introduced the construction of new astronomical tables. But it was in the sixteenth century, that a new era for astronomy, as a science of observation, was opened up, under the auspices of the Landgrave of Hesse, William IV., who enriched the science by a long series of observations; and also procured the protection of Frederick II. of Denmark to Tycho Brachè, the greatest astronomer of his time. The King of Denmark gave the island of Hveen, in the Sound, to this astronomer, for the purpose of there establishing the first observatory of modern times, to which he gave the name of Uranienbourg, all the cost and expense of which was defrayed by the prince. The instruments necessary for this establishment were constructed in a workshop appropriated to the purpose, in which the first German tradesmen worked under the eye of Tycho. He began his observations there in 1577, with twenty-eight different instruments, and, with the help of many assistants, continued them till 1597. This invaluable treasure of observations became, in the hands of his scholar and friend Kepler, the instrument by which were effected the grand discoveries concerning the true forms of the planetary orbits, and concerning the laws of the movements of these planets in their orbits,-discoveries which have immortalized the name of Kepler, and which soon after gave birth, the offspring of Newton's genius, to the whole of physical astronomy. After the death o King Frederick, the Emperor Rudolph became the patron or Tycho, and invited him to Prague, where he was associated with Kepler.

The extraordinary progress which astronomy made in the -17th century, principally by the discovery of the telescope, is well known; for by it, new means were acquired for revealing to the inhabitants of the earth the wonders of the heavens. Many observatories were then constructed, under the patronage of enlightened princes, at Copenhagen, Paris, Greenwich, &c.; and in the following century, others arose at Manheim, Palermo, Stockholm, and in other places. It would here occupy too much space to relate all that has been done by princes, during this period, for the advancement of astronomy. None can be ignorant how much we are indebted for our knowledge of the