2 REPORT 1865. 



redder parts of its disk are land, and the greyer parts sea, appears to be verified ; 

 recent observations also confirm the view that snow is visible in its polar regions. 

 Comparing the latitudes of arctic climates on Mars with those on the earth, it bar? 

 been concluded that the temperature on the two planets is not very different. The 

 solar radiation in the two cases is, of course, very disproportionate ; but the expla- 

 nation of the result is to be sought in the action of a dense atmosphere, which, as 

 Professor Tyndall has shown, serves to retain large quantities of heat which would 

 otherwise radiate into space. 



Mr. Lassell has communicated to the Royal Astronomical Society an ephemeris 

 of the satellites of Saturn, now finally reduced to four. 



The number of the minor planets continues to increase. M. Serret has presented 

 to the Academy of Paris a theory of the movement of Pallas, complete as regards 

 the perturbations of the principal planets. He promises a second part, discussing 

 the influence of the minor planets, in which he states that he has arrived at some 

 curious and unexpected results. 



Although the subject of auroras more properly belongs to that of terrestrial mag- 

 netism, it may here be mentioned that the height of these phenomena has been 

 determined to be from 35 to 290 miles. Meteors and falling stars, whose periodic 

 visits in August and November are well known, have both, by the labours of 

 Alex. Herschel, Quetelet, and Secchi, been shown to be minute planetary bodies, 

 differing only in size. When visible, they pass at a height of from fifty-two 

 to seventy-three miles above the surface of the earth. M. Deville has even at- 

 tempted to account for the known depression of temperature in February and May, 

 and the elevation in August and November, by their position intercepting the heat 

 of the sun during the former periods, and preventing the heat from the earth radi- 

 ating into space during the latter. 



Before leaving our solar system, we must notice the discussion which has arisen 

 respecting an expedition to the Antarctic regions to reconnoitre for practicable 

 stations for the observation of the transit of Venus in 1882. It is unnecessary to 

 remind this section that upon accurate observations of this phenomenon, at proper 

 points upon the earth's surface, will depend a verification or otherwise of M. Fou- 

 cault's correction of the sun's distance, due to his new measurements of the velocity 

 of light. The question of the expedition, however, will doubtless be fully discussed 

 in the geographical section. 



A celestial atlas, just published by M. Dien, promises to surpass all its prede- 

 cessors in accuracy of detail. The difference of longitude between points on the 

 great arc of parallel — Bonn, Nieuport, and Haverfordwest — has been carefully ob- 

 served ; so has the longitude of the observatory at Glasgow. 



The usual amount of attention has been paid by observers and calculators to the 

 subject of comets and their orbits. But, besides this, M. Hock, in a paper presented 

 to the Royal Astronomical Society, has argued in considerable detail in favour of 

 his view that comets move in parabolic and hyperbolic orbits, not in ellipses — tbat 

 they are not isolated bodies, but consist of groups of fragments of bodies broken 

 up by the sun or planets. 



Passing to the more remote celestial objects, Mr. Iluggins has been continuing 

 his observations on, and has determined, the spectra of the fixed stars and nebula', 

 of which we may hope to hear some further particulars. In the meantime, I will 

 notice only one point, but that a very curious one. Lord Rosse and Professor Bond 

 find, by telescopic observations, that the brighter portions of the great nebula in 

 Orion are apparently resoluble into stars. Mr. Huggms's analysis, on the other hand, 

 gives a spectrum consisting of three bright lines only, indicating a gaseous condition. 

 An explanation of this apparent contradiction is perhaps to be found in the sugges- 

 tion that the bright points shown by the telescope are not stars in the ordinary 

 sense of the term, but condensed parts of the nebulous fluid. Imagination would 

 lead us to suppose that we have here before us a stage of cosmical process interme- 

 diate between nebula and stars — the formation of a sun ; but strict science forbids 

 us as yet to' adopt this as an ascertained conclusion. 



Spectrum analysis continues to receive further additions at the hands of the chair- 

 man of our Kew Committee, Mr. Gassiot, who has carried the question so far as to 

 construct an apparatus for determining whether the so-called fixed lines of the 



