SCIENCE. 



165 



SCIENCE: 



A Weekly Record of Scientific 

 Progress. 



JOHN MICHELS, Editor. 



Published at 



229 BROADWAY, NEW YORK. 



P. O. Box 3838. 



SATURDAY, OCTOBER 2, 1880. 



We are pleased to remark some prospect of renewed 

 astronomical activity at the Dearborn Observatory, 

 Chicago. This institution was, for a period of more 

 than ten years, in possession of the largest refracting 

 telescope in existence — the object glass of which has 

 an aperture of eighteen and one-half inches. The 

 great telescopes which have since been built, 

 and are now in process of construction, have 

 the apparent effect of dwarfing the Chicago tele- 

 scope, which, at the time it was made, was a 

 great advance on every thing that had preceded 

 it. There seems to be the best of reason for 

 doubting, however, whether any other instrument at 

 present in existence is surely superior to the Chicago 

 refractor for efficient astronomical work. Mr. S. W. 

 Burnham, distinguished for his researches in double 

 stars, speaks with authority in this matter — " I know 

 of no object, faint or otherwise, which has been seen 

 at Washington or elsewhere, that cannot be seen per- 

 fectly here [at Chicago] and accurately measured." 

 Professor Newcomb, in his " Uranian and Neptunian 

 Systems, Investigated with the 26-inch Equatorial of the 

 United States Naval Observatory, Washington," re- 

 marks that Ariel and Umbriel, the inner satellites of 

 Uranus, " are visible only when the atmosphere is 

 very fine, and are then difficult objects," and considers 

 it very doubtful whether these objects have ever been 

 seen with an aperture so small as twelve inches. 

 Director Hough, of the Dearborn Observatory, states 

 that near the time of the planet's opposition, these satel- 

 lites can readily be seen and measured, under ordinary 

 atmospheric conditions, with the Chicago telescope. 

 If, as is quite possible, the Chicago refractor should 

 prove to be quite as effective in actual observation as 

 some of the larger telescopes of a later day, we shall 

 have another of those instances frequently forced 

 upon the astronomer, wherein his computation of the 

 adequacy of a particular instrument does not tally 

 with its observational effectiveness. Every astronomer, 

 then, must regret that so competent an instrument 

 must, through lack of endowment, be lying mainly 

 idle, or, at the most, only employed by those who are 

 able to turn it to scientific observation without 

 pecuniary compensation. The valued work of Mr. 

 Burnham with this instrument, in the discovery and 

 observation of double stars, is well known. Professor 



Hough, in connection with Professor Colbert, con- 

 ducted a series of observations of Jupiter at the late 

 opposition. Owing to the discordance in the deter- 

 minations of the ellipticity of the planet's disk from 

 observation, their attention was given to a new deter- 

 mination of this quantity, with these results : 



By Professsr Hough , 1 — 16.23 



By Professor Colbert 1 — 16.73 



The English Nautical Almanac uses the value 

 1-13.71, while the value 1-16.40 is adopted in the 

 American Ephemeris. With the same magnifying 

 power, 638 diameters, the absolute polar and equa- 

 torial diameters of the planet were observed to be, 

 for the mean distance of Jupiter from the Sun : 



Polar. Equa'l. 



By Professor Hough 36". 319 38°. 704 



By Professor Colbert 36". 030 38". 316 



Assuming a solar parallax of 8". 81, the measures of 

 Professor Hough give for the equatorial diameter 

 90,570 miles, and for the polar diameter 85,000 

 miles. 



Measures of the angle of position of the north edge 

 of the equatorial belt show that it had the same direc- 

 tion around the entire circumference, and that this 

 direction (exactly parallel to the planet's equator) was 

 maintained throughout the entire opposition. Very 

 complete measures of the apparent latitudes and 

 widths of the several components of the belt system of 

 Jupiter were also made, the great red spot co-inciding 

 very nearly with one of these belts. The reduced 

 measures of apparent latitude show very clearly that 

 the belts were arranged symmetrically on either side 

 of the equator, three being in the northern and three 

 in the southern hemisphere of Jupiter. The report on 

 these observations is accompanied with wood-cuts 

 showing the red spot, the belt system, and, to some 

 extent, the structure of the great equatorial belt. 

 From the observations of this spot, Professor Colbert 

 has computed the time of rotation of the planet on 

 its axis: he finds it to be oh. 55m. 34.2s., differing 

 about eight seconds from the value hitherto consid- 

 ered the most probable. 



Micrometric measures of the diameters of the four 

 satellites of Jupiter were made on three nights, the 

 resulting values being, at mean distance of the planet: 



1. 

 1". 114 



in. 



r.778 



IV. 



i"'457 



The actual diameters of the satellites given by 

 these measures are 2610, 2290, 4160, and 3410 miles, 

 respectively. 



But the superior quality of the object glass of the 

 Chicago refractor is more effective with such objects 

 as the satellites of Uranus ; micrometric observa- 

 tions were secured as follows : 



Of Ariel, on four nights. 

 Of Umbriel, on one night. 

 Of Titania, on eight nights. 

 Of Oberon, on seven nights. 

 And this, notwithstanding that the observations were 

 begun late in the opposition, and were interrupted by 

 an unusual amount of cloudy weather. We should 

 like to see the superior light-gathering power of this 

 object glass turned toward systematic figuring of the 

 fainter nebulae. 



We may mention the meridian circle of the Dear- 



