7S 



k NOWLEDGE, 



[April, 1902. 



in connection with the great comet which bears bis name. 

 This comet, detected by him in Florence as a faint 

 nebulous spot, on June 2ud, 1858, developed in a few 



Arcetri Observatory, Florence (Soutli Front). 



months' time into one of the most superb celestial 

 spectacles ever witnessed, its nucleus rivalling Ai-cturus 

 in splendour, while the tail extended over an arc of forty 

 degrees, forming a magnificent object in the autumn skies 

 of that year which it graced for one hundred and twelve 

 days. The building operations, which lasted some three 

 years, being completed, the new Observatory was formally 

 opened on October 27th, 1872. Donati, however, was 

 unhappih' not destined to long enjoy the advantages of 

 its improved position, for he died suddenly on September 

 ISth, 1873, but forty-seven years of age. For a brief 

 interval, under the care of an assistant, the Observatory 

 came, in 1875, under the management of Temjjel, who, 

 adding the skill of an accomplished draughtsman to his 

 accuracy as an observer, executed a quantity of very 

 beautiful drawings of nebulae with the aid of the A.mici 

 equatorial, noticed above, and smaller instruments. During 

 Tempel's directorship, however, certain structural defects 

 had made themselves apparent, so that at his death in 

 1889 considerable alterations were vmdertaken which have 

 brought the building and its instrumental equipment into 

 line with the most exacting modern requirements, and, 

 under the present Director, the Observatory has taken up 

 an important position among the observatories of Italy. 



Such, in brief, is the history of an institution which may 

 be said to have sprung directly from the founder of ob- 

 servational astronomy, and it was but fitting that Prof. 

 Abetti, in his inaugural address delivered at the re-opening 

 of the University of Florence for the present session, 

 should have drawn attention to the close relationship 

 existing between Galileo and his school, and the Ai-cetri 

 Observatory. Indeed, the spirit of Galileo seems to per- 

 vade the classic hill of Arcetri on which the Observatory 

 stands, for close by lies his villa, il Gioiello, where he was 

 visited by Milton, in 1638, and where he spent the de- 

 clining years of his life, having been chiefly attracted 

 towards this spot by reason of its proximity to the Convent 

 of San Matteo, where his two daughters, Suor Maria 

 Celeste and Suor Arcangela, lived as nuns. It was iu this 

 villa that Galileo sought retirement after returning, still 

 a prisoner, from his memorable visit to Rome, whither he 

 had been summoned by Pope Urban VIII. to abjure 

 before the tribunal of the Inquisition the " heresies " of 

 the Copernican doctrine ; and it was here that his 

 favourite daughter, Suor Maria, undertook the filial task 

 of reciting weekly the seven ])enitential psalms which 

 formed part of her father's sentence. Now it was that 

 the great astronomer was justly characterised by Byron 



as "the starry Galileo with his woes," for he was soon 

 struck with total blindness. " The noblest eye," as his 

 friend Castelli expressed it, " was darkened— an eye so 

 gifted that it may be said to have seen more than the 

 eyes of all that are gone, and have opened the eyes of all 

 that are to come." His death followed but a few years 

 afterwards, on the 8th January, 1642, wheu he was in the 

 seventy-eighth year of his age. 



Its associations alone would thus ensure for Arcetri an 

 honoured position among observatories, quite apart from 

 the fact that it occupies a site which, for historic interest 

 and natural beauty of surroundings, is almost without a 

 rival in Europe. Standing on the terrace of the Observa- 

 tory, the eye ranges over a magnificent prospect, which is 

 bounded on the eastern horizon by the wooded heights of 

 Vallombrosa, and on the western by the distant Carrara 

 Mountains, while southward lie the beautiful hills of 

 Chiauti, and on the other side, Fiesole, and the lofty spurs 

 of the Apennines, at whose foot lies Florence in the broad 

 "valley down which the yellow Arno steals silently 

 through its long reaches to the sea." 



ASTRONOMY WITHOUT A TELESCOPE. 



By E. Walter Maundee, f.r.a.s. 



Xn.— THE MARCH OF THE PLANETS. 



The nightly procession of the stars across the sky was not 

 the only celestial movement which impressed the observers 

 of old. The coming and going of the planets held an 

 even stronger attraction for them, and the mystery of 

 their wanderings, which seemed at first sight to be so 

 lawless, was the subject of much deep speculation. But 

 this field of work has been so completely occupied in 

 modern times by the transit circle and allied instruments 

 that it is now hopeless for the " Astronomer without a 

 Telescope" to dream of obtaining results of any real value. 

 The only thing that he can do is to imitate his fore- 

 runners and to familiarise himself with the apparent 

 motions of the planets as they present themselves to the 

 naked eye. 



In this work he will find that the five planets within the 

 reach of his unaided sight divide themselves into three 

 groups. The first group includes Mercury and Venus, 

 which moving in orbits interior to that of the earth, can 

 never come into opposition to the sun, but oscillate 

 backwards and forwards on either side of him. Both of 

 them are therefore most easily observed when they are at 

 their elongations. Of the two. Mercury, being much the 

 least bright, since he is smaller, and has a less reflective 

 surface than Venus, is by far the more difficult object, a 

 difficulty increased by the fact that his elongation cannot 

 under the most favourable conditions amount to 28°, 

 whilst the greatest elongation for Venus is nearly 48^. 

 For reasons corresponding to those which were considered 

 in the preceding chapter as regulating the most favourable 

 conditions for observing heliacal risings and settings of 

 stars, the most favourable position for Mercury to be seen 

 as an evening star is when his eastern elongation occurs 

 near the spring equinox ; his most favourable position for 

 observation as a morning star is when his western 

 elongation occurs near the autumnal equinox. 



Comparatively few dwellers iu England have seen 

 Mercury with the naked eye, unless they have persistently 

 searched for liini, and hence the idea has ariseu that 

 there was something very remarkable about the kuow- 

 ledjge which the ancients had of this planet. But as 

 Colonel Mark wick remarked in a paper iu Knowledge 

 (July, 1895, p. 152) — "To anyone who has seen that 



