ASTRONOMICAL PHENOMENA AND PROGRESS. 



stations can be found in the antarctic regions 

 for observation of the transit could doubtless 

 be rendered at the same time not less profitable 

 than an arctic exploration, by combining with 

 this main purpose, those of observations in con- 

 nection -with geography, geology, hydrography, 

 magnetism, meteorology, natural history, and 

 other subjects for which the localities may be 

 suitable. 



Prof. Airy had previously discussed, in an 

 elaborate paper, the circumstances of the coming 

 transit, and especially in reference to the selec- 

 tion of stations for observation, his paper being 

 published in the "Monthly Notices" (R. A. S.). 

 In explanation, it may be stated, that the method 

 of determining the sun's distance by means of 

 the transit, depends on a comparison of the 

 lengths of time occupied in the passage of the 

 planet across the solar disc, as witnessed from 

 different points on the earth's surface ; and the 

 result is more nearly correct in proportion as 

 the differences in the apparent duration of the 

 transit are made to approach nearer to the max- 

 imum of possible difference (this geometrical 

 maximum being expressed by 2.00). The tran- 

 sit of 1882 will occur on the 6th of December ; 

 its duration will be nearly six hours, namely, 

 from about 2 hours to about 8 hours, Greenwich 

 mean solar time. Now, the instant and place 

 (true perhaps to a second of time and arc) at 

 which the planet will enter and leave the solar 

 disc, are known ; and, of course, also, exactly 

 how the earth will be hanging in space at the 

 time how its axis will be situated in reference 

 to the plane of the ecliptic, and to the line of 

 the apparent path of the planet across the solar 

 disc. Suppose a plane cutting the centre of the 

 earth, and tangent to the sun's limb at the point 

 of the planet's ingress upon fhe disc : then, of 

 two sets of observers at points on the two sides 

 of the earth remote from this plane, one set will 

 (as its distance approaches a semi-diameter of 

 the earth) see the ingress accelerated, while 

 the other set will, in like proportion, see it 

 retarded. Suppose another plane, cutting the 

 centre of the earth and the point of the planet's 

 egress from the disc : in like manner, observers 

 on the two sides of the earth remote from this 

 plane will respectively see the egress retarded 

 and accelerated. The desiderata, then, are 

 suitable stations for observing, at both or all 

 of which the sun shall be visible at 2 hours and 

 at 8 hours Greenwich mean time ; while at one 

 set of these, the ingress shall be accelerated and 

 the egress retarded, and at the other the ingress 

 shah 1 bo retarded, and the egress accelerated 

 thus securing the greatest practicable difference 

 of apparent durations of the transit. 



Prof. Airy finds that the latter of these two 

 conditions is well answered by stations on the 

 seaboard of the United States (those toward 

 the Gulf of Mexico having the advantage of a 

 higher sun at egress), and at Bermuda. At 

 these places the duration of transit is shortest ; 

 along the Atlantic seaboard, the mean retarda- 

 tion of ingress is 0.95, the mean acceleration of 



egress 0.83 nearly: total shortening, 1-78 (pos- 

 sible maximum, 2.00). At Bermuda, the par- 

 allactic values are, for ingress, 0.9, and for egress 

 0.9: total shortening, 1.80. 



For the parts of the earth, however, at 

 which the duration of transit will be longest, 

 the choice of stations is more limited and the 

 practical difficulties are greater. The station 

 must be on the antarctic continent, and at some 

 point at which the brief descent (in a practica- 

 ble latitude) of the sun at that season below 

 the horizon shall occur and terminate between 

 the hours of 2 and 8 Greenwich mean time. 

 As the sun will be low at best, it is further de- 

 sirable that the hour angles of these two times 

 shall be as nearly equal as possible. The re- 

 quirements can only be satisfied by a location 

 in about 65 S. lat. and about 105 E. long. ; 

 and therefore somewhere between Sabrina Land 

 and Repulse Bay. The value for acceleration 

 of ingress would here be 0.95, that for retarda- 

 tion of egress about 0.66 : total lengthening, 

 1.61. Combining this with observations at 

 Bermuda, the whole difference of durations 

 would be 3.41 (geometrical maximum, 4.00). 

 Supposing the latitude 65 S., and the sun's 

 south polar distance 67 27', the sun's altitude 

 at each observation would be 4 6' ; which, if 

 the sky were not liable to banks of haze near 

 the horizon, and the weather should prove 

 favorable, would suffice. A point on the ant- 

 arctic continent nearly opposite that now con- 

 sidered, would show the sun at both ingress 

 and egress; but the total lengthening would 

 be only about 0.6, against 1.61 near Sabrina 

 Land. 



In accordance with these conclusions, Mr. 

 Airy, in the letter before referred to, urges an 

 early exploration of the region between this 

 coast and Repulse Bay ; and he then continues : 



" The points to be ascertained are (1) wheth- 

 er the coast is accessible on December 6th ; (2) 

 whether a latitude of 65 can be reached ; (3) 

 whether the sun can usually be seen well on 

 December 6th at three hours on each side of the 

 lower meridian. * * * Should the answer 

 to the first or third of these questions be nega- 

 tive, then it would be proper to examine other 

 portions of the South Continent, say in longi- 

 tude not very different from 5 h [75] West, but 

 with no particular restriction, except that of 

 gaining the highest possible South latitude. 

 And the only point for inquiry would be, how 

 well the sun^aa usually be seen on December 

 6th, at 2 h and 8 h Greenwich mean solar time." 



Asteroids. Mr. Pogson, of Madras, an- 

 nounced the discovery, May 3d, 1864, of a 

 supposed new asteroid, and to which he as- 

 signed the name and number, Sappho (80). T. 

 Oppolzer, in a letter to Mr. Airy, asserted, from 

 comparison of the elements of the two, the 

 identity of this planet with M. D 'Arrest's, 

 known as Freya (76). Mr. Pogson, in a later 

 note, admitted this identity, remarking that the 

 name Sappho is thus at liberty for future use. 

 Astronomers seem not yet to have changed the 



