216 Chronicles of Science. [April,. 
He finds that the refraction of Bessel’s ‘ Fundamenta’ require to 
be diminished in the proportion of 0:99797 to 1, to be correct 
for Greenwich. He has examined also the Melbourne observations 
for 1863, 1864, and 1865, to test the accuracy of the proposed 
diminution of the Greenwich tabular refractions. A somewhat 
remarkable result has attended the inquiry. He finds evidence of 
a difference in mean refraction towards the south and north at 
Melbourne. He ascribes this to the position of Melbourne. ‘The 
refractions towards the south are greater, because the ocean les to 
the south, so that there is more moisture in the air-masses which 
lie in that direction. The refractions toward the north are less, 
because the effective strata of air have been to a considerable extent 
deprived of moisture. 
Mr. Penrose has attempted to facilitate the prediction of occul- 
tations and eclipses by the application of geometrical constructions. 
Such methods are not, perhaps, likely to supersede the more 
rigorous processes adopted by the compilers of our ephemerides, 
but they are valuable in many respects. We believe that there is 
room for a great extension of geometrical processes to the illustra- 
tion of many astronomical phenomena which at present are either 
dealt with by abstruse processes intelligible only to the advanced 
mathematician, or so roughly and imperfectly illustrated that the 
amateur astronomer is more likely to adopt incorrect impressions 
than to acquire any real information. 
Mr. Browning has ascertained that the colours of stars are not 
nearly so intense in telescopes of large aperture as in small instru- 
ments. 
The following summary of the results of the examination of three 
long periods for the determination of Mars’ Rotation-period may 
prove interesting. Each period begins from Hooke’s observation of 
Mars, on March 12, 1666, 12h. 20m. (astronomical time and new 
style), and the periods extend severally,—(i) to April 24, 1856, 
10h. 50m., (ii) to November 26, 1864, 11h. 46m., and (ii) to 
February 23, 1867, 6h. 15m. :— 
P Cor, fi Cor. fi C ted No. of |Resulting Rotati 
Int. Int. in Seca. Gaaes ieties Hosea Int. fs Eeoadeks Bataiions Period in Saad ¥ 
(i) | 5999524200 — 0° —12° | 5999521246 67682 88642°737 
(ii) | 6270650760 —248° 0° | 6270589696 70740 88642°734 
(iii) | 6341394300 —273° +3° | 6341326590 71538 88642°734 
Mr. Proctor mentions that nothing is doubtful in this table except 
the correction for Geocentric longitude (which, however, may be 
depended on as being within 1° of the truth) and the correction for 
phase. The last correction depends only on the accuracy of the 
drawings of Mars by Hooke—at one end of the intervals, and by 
