260 Chronicles of Science. [April, 



extended, in combination with those made upon CepLei 51 and B 

 Ursfe Minoris from 1851 to 1865, be obtains for the final value 

 of the constant of nutation 



9"-134-0-55p + 2-02 5^ + 0-29 5?w - Q-G 5c. 



•where p, Sp, Bm, and Be are the possible errors in the assumed 

 estimates of the proper motion of the pole-star in E. A, and N. 

 P. D, and of B Ursaj Minoris, and of 51 Cephei in N. P. D. re- 

 spectively. On account of the bearing of the constant of nutation 

 upon our estimate of the moon's mass and of the sun's distance, 

 these investigations are of extreme importance. 



The Astronomer-Pioyal has supplied another of his valuable 

 papers on the preparatory arrangements which will be necessary 

 for the efl&cient observation of the transits of Venus in the years 

 1874 and 1882. It is almost impossible fairly to represent the 

 nature of the present paper in the brief space available in these 

 pages. Indeed the eight octavo plates which accompany the 

 paper, and the two which illustrate Mr. De la Kue's paper on the 

 same subject, are very necessary to the proper interpretation of 

 Mr. Airy's remarks. But while referring the reader who would 

 thoroughly master the views presented in these admirable essays 

 to the papers themselves, we may point to the following important 

 conclusions derivable from Mr. Airy's calculations : — 



1. For observing the ingress of Venus as accelerated by parallax 

 (in 1874), Owhyhee and the neighbouring islands, the Marquesas 

 Islands, the Aleutian Islands, and the mouth of the A moor are 

 more or less favourably situated. 



2. For observing the ingress retarded by parallax, Kerguelen 

 Island and Crozet's Island are well situated though geographically 

 unfavourable. Next in order come Eodriguez, Mauritius, and 

 Bourbon Islands, Madras, and Bombay. 



3. For observing the egress accelerated by parallax, a part of the 

 Southern Continent if available would be the best place. Passing this 

 region over, we come next to the Auckland Islands, Canterbury, 

 Wellington, and Auckland, Norfolk Island, Melbourne, and Sidney. 



4. For observing the egress retarded by parallax, Omsk, Orsk, 

 Astraehan, Erzeroum, Aleppo, Smyrna, and Alexandria are well 

 situated. 



All these cases refer to the transit of 1874. As regards the 

 transit of 1882, it is noteworthy that there is a possibihty of ap- 

 plying the same method as was employed in 1769, — that is, deter- 

 mining the sun's distance from the dilierent duration of the transit 

 as observed from different points of the earth's surface. This 

 method, Mr. Airy remarks, tails altogether in 1874, and there is 

 not much prospect of its being successfully a])plied in 1882. Both 

 these transits take place in ]3ecember, when the southern or sea- 



