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Washington glass, but Mr. Grubb in his own practice finds sensible flexure even in 15-inch glasses and uses three intermediate supports for these (six in all), and in the 27-inch Refractor which he is making for the Vienna observatory he expects to use six such. This advantage of the Reflector could be reduced, however, as Mr. Grubb himself suggests, either by introducing a central support, or, more elegantly, by having an air-tight tube for the Refractor, hermetically sealed and filled with air under pressure. The eye end could be sealed by a Barlow lens of low power. This air would form the most perfect of supports for the objective, and the plan is quite feasible, though novel. Mr. Grubb has worked out the details of this plan, and finds that for an objective of forty inches aperture and six hundred pounds weight, two thirds of whose weight it is required to support by the air-cushion, a pressure of one third of a pound per square inch (one fiftieth of an atmosphere) would suffice.

B. This advantage increases rapidly with increased size. With regard to the practical difficulties in each case and the most promising means of overcoming these, Mr. Grubb adduces from his own extensive experience the most important facts. For Refractors, it appears to him "that the chances of obtaining 40-inch discs of glass, in the present state of the art of glass-making, are remote.” The difficulties of figuring large objectives can be overcome by the opticians without doubt. Certainly Mr. Grubb in Europe, and the Clarks of Cambridgeport, will undertake to figure an objective of any size. For Reflectors, the difficulties of getting discs of glass over six feet are probably insuperable, as no one of the glass-makers in Europe is now willing to undertake to make a disc of that diameter (although the quality of the glass is here of no moment), and therefore silver-on-glass Reflectors of that size are for the present out of the question. With regard to metallic specula of large dimensions Mr. Grubb says that his own experiments lead him to believe that we shall soon be able to produce metallic mirrors with a reflecting power twenty-five per cent greater than those formerly made; they certainly can now be made of six feet aperture. It is probably in this direction that Mr. Grubb looks with the greatest hope. His final conclusion, "that no one kind of telescope is best for all kinds of work, and that in the choice of telescopes reference must be made to the work that the instrument is intended for " and to the circumstances under which it is to be employed, is

so eminently just that it simply requires to be stated to be ad

mitted.

The Comets of 1877.

The recent dearth of comets has been supplied in 1877 by the discovery of three. Comet a was discovered by Borelly of Marseilles, on February 8, and was visible as a telescopic object till March 18 in Europe, but was observed by the 26-inch telescope at Washington so late as March 30. It had the usual comet spectrum. Comet b was discovered by Winnecke of Strassburg, on April 5, and independently by Block of Odessa, on April 10. Young of Dartmouth and Wolf of Paris have investigated its spectrum, which is of the usual type. Comet c was discovered by Swift of Rochester on April 10, and independently by Borelly on the 14th. It was at first supposed that Comet b, whose elements are similar to those of 1827.II. and 1852.II., might prove to be periodic, but according to Hind this is not likely. There is a strong resemblance between the elements of Comet c and those of the Comet of 1762. D'Arrest's periodic comet was detected on the 30th of July by M. Tempel, of Florence.

Astronomical Expedition to Ascension Island.

Mr. David Gill of England is to take up his residence at Ascension Island, for the purpose of making heliometric observations of Mars to determine the solar parallax. The heliometer to be employed is the one used by Mr. Gill in the Transit-of-Venus Expedition of Lord Lindsay in 1874, in which Juno was observed and the parallax 8".82 deduced. This expedition is of great importance in many ways, as it is quite possible that from its results the best determination of solar parallax may be had, the method employed admitting of great refinement. The support given to the expedition is also noteworthy, as the Royal Astronomical Society guarantees the expenses, £500, and as several observatories will join in the fixing of the star places, etc. It contrasts with the unfortunate expedition of Gilliss (1849-52), who, on his return to the United States from Chili, found that his brilliant labors in the same field, although by a different and less independent method, had been practically in vain, through the feeble support given by Northern observers.

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The new Durchmusterung.

Astronomers will never cease to be grateful to Argelander and his assistants, Krueger and Schoenfeld, for the Durchmusterung des Nordlichen Gestirnten Himmels, which embraces all the stars, of the first nine magnitudes, from the North Pole to 2° of south declination. This work was begun in 1852, and at its completion a catalogue of the approximate places of no less than 324,198 stars, with a series of excellent star-maps giving the aspect of the northern heavens for 1855, was at the service of astronomers, and has been in the most constant use from that time forward. Argelander's original plan was to carry this Durchmusterung as far as 23° south, so that every star visible in a small cometseeker should be registered. His original plan was abandoned, but his former assistant and present successor at the observatory of Bonn, Dr. Schoenfeld, is now engaged in executing this important work. The same methods will be followed by Schoenfeld which were so successful formerly; the equinox of 1855 is chosen as the fundamental one; and almost the only changes are the adoption of a telescope of six inches aperture for the work, and a closer discrimination of the magnitudes of the fainter order of stars. In the prosecution of the plan, Schoenfeld has already determined the position of 74,885 stars; and astronomers in the northern hemisphere will soon possess an index, as it were, to every star likely to be used in their observations.

New Satellites to Mars.

On the 16th of August, since the above was written, Professor Hall, in charge of the 26-inch equatorial of the Naval Observatory at Washington, discovered a faint satellite to Mars. From the observations up to the present date, it appears that its time of rotation is about thirty hours, and its greatest distance from the centre of Mars about eighty seconds of arc. It appears to be of the 13-14 magnitude. The mean distance of this satellite is between 14,000 and 15,000 miles, which is less than that of any known planet.

On the 18th of August Professor Hall suspected the existence of another satellite interior to the first; at the date of writing this no further observations are at hand. The discovery of these two satellites is one of the most important astronomical events of the century, being paralleled only by the discovery of Ariel and Umbriel by Lassell, and of Hyperion by Lassell and Bond.

ART. XI. CONTEMPORARY LITERATURE.

1.-1. Renaissance in Italy: The Age of the Despots. By JOHN ADDINGTON SYMONDS. London Smith, Elder, & Co.

pp. xvi, 574.

2. The Revival of Learning. London. 1877. pp. xv, 546. 3. The Fine Arts. London. 1877. pp. xiv, 539.

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1875. 8vo.

Ir is Mr. Symonds's purpose in the three handsome volumes before us (to be completed by one on Italian Literature) to give a detailed account of that wonderful intellectual movement in the fifteenth century which for want of a better term we name Renaissance, the new birth of humanity brought about by the revival of classical letters, or rather of the classical spirit. In a narrow sense the Renaissance is the period during which the Italians became conscious of their Latin ancestry and sought to revive the literature and arts of ancient Rome. In a broader sense the Renaissance is the transition period from the Middle Ages to the modern world, and it is in this sense that Mr. Symonds understands it and attempts to describe it.

A mere history of the effects of a certain spirit would be unsatisfactory without some account of the growth of that spirit and the external causes that modified it and caused it to assume peculiar and phenomenal shapes. This is the case with the history of the Renaissance. The new spirit of classical learning, with the momentous changes it wrought in the moral constitution of mankind, modified powerfully Italian society of the fifteenth century, but it was itself influenced by it, and the rapid assimilation of the new spirit could not have taken place without a certain pre-existing state of society. The author devotes the first volume of his work to giving a picture of this society in a survey of the political and social condition of Italy during the fifteenth century. It may be doubted whether any period of modern history possesses so many individual characters who have exercised on posterity such powerful fascination as Lorenzo de' Medici, the Borgias, Savonarola, and Michael Angelo, names which represent the extremes of the tendencies of their age. It was the age of immense contrasts, of the grossest immorality and most fervent piety, of outward Christianity and inward paganism, of wild bloodthirstiness and gentle manners, the age that produced a Vittoria Colonna and a Lucrezia Borgia. It is, in short, an age that

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must always remain a psychological problem and baffle the fascinated student. Mr. Symonds gives a vivid picture of this immoral, tyrantridden Italy of the fifteenth century, and indicates the conditions which were favorable to the new spirit which manifested itself, first, in what is known as the Revival of Learning. The numerous courts of wealthy and able despots were so many centres of patronage where the tyrant assumed the mask of Mæcenas and lavished the state treasures on manuscripts of Cicero and Homer. It is difficult for us now to comprehend the boundless enthusiasm for classical learning which possessed the whole nation. We must, however, bear in mind that it had all the charm of freshness. In Petrarch's day Greek was practically unknown in Italy, and there is something touching in the middle-aged Boccaccio endeavoring to catch a glimpse of Homer's grandeur, and becoming the first Greek scholar in Italy. This charm of freshness attached to Latin also, for although it was the language of the Church and State, it had departed immeasurably from the models of classic times, and the language of Cicero was as new as the language of Homer.

In his second volume the author describes the Revival of Learning from Petrarch and Boccaccio to its final stage in Bembo and the purists. We witness the eager search after manuscripts, the careful collation of texts, the founding of the great libraries at Florence and Rome, the rise of learned academies, and the final pedantry which brought discredit upon the whole movement and degenerated into affectation. One of the most interesting characters of this period is the wandering professor, a perambulating library, who expounded the new-found classics to enthusiastic crowds, and when he had finished the minute exposition of the few authors to whom he had devoted his life moved on to another city where his lectures were fresh. They were for the most part arrogant, irascible men, puffed up with the consciousness that they were the only receptacles of learning, and their quarrels form one of the most curious chapters in the history of the period.

The large mass of biographical details in this volume wearies the reader; it is, however, relieved by many interesting disquisitions on libraries, the introduction and early history of printing, and the Latin literature of the Renaissance. It is not until we can form an idea of the whole movement and its results on the individual and society that we can appreciate the efforts of a Poggio Bracciolini in collecting manuscripts or the munificence of a Cosimo de' Medici in founding public libraries.

The new spirit was not manifested alone in literature, it soon showed itself in art; and it is to this side of the movement that the third volume of Mr. Symonds's work is devoted. His purpose, as he says in his Pref

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