1873.] President's Address. 7 



graphic records, some will employ Mr. De La Rue's photoheliograph ; 

 some will endeavour to arm it with M. Janssen's arrangement for taking 

 numerous pictures of Venus at small intervals ; some prefer a horizontal 

 telescope 40 feet in length, into which the sun's rays will be thrown by a 

 large plane mirror moved by a heliostat, and by which the primary 

 image of the sun will be photographed. A working model of the Transit 

 has been established at the Eoyal Observatory, by means of which the 

 singular optical phenomena are well seen. My own estimate, and that 

 of my experienced friends, on the amount of uncertainty, reduces it 

 low ; but I believe that my younger observers are not so successful. 

 German astronomers have proposed to make use of observations of the 

 Minor Planets (Flora in the present year) for measuring the Solar 

 Parallax ; but I conceive that Mars in 1877 will be very far superior. 

 The publication of the Eclipses of 1870 and 1871 is still delayed, mainly 

 by troubles with engravers. I am happy to state that, at the instance of 

 the Smithsonian Institution, and by the liberality of the Anglo- American 

 Company (who have declined all commercial remuneration), telegraphic 

 announcements of astronomical discoveries are now made direct from the 

 United States to Europe, and vice versa. 



In G-eodesy and related subjects an important repetition of Caven- 

 dish's experiment has been made by MM. Cornu and Bailie, using, for 

 the attracting material, hollow spheres filled with mercury, which was 

 transferred from one sphere to the other; the mean density of the 

 earth thus obtained is 5'56. It is proposed in Erance to repeat the 

 observations for the great arc of meridian. Allusion was made in the 

 last two Addresses to the interruption of the Indian pendulum-observa- 

 tions by the death of Captain Basevi ; the pendulums (two the property 

 of this Society, and two belonging to the Russian Government) have 

 been brought to this country ; and observations of them have been made 

 at Kew Observatory by Captain Heaviside. It is proposed, I believe, to 

 combine with these observations a re-observation of Kater's double- 

 knife-edge pendulum. 



Geographical research has been very active. The ' Challenger,' after 

 three times crossing the Atlantic, was last reported at Bahia. One result 

 of her operations is the establishment of a general uniformity of depth, 

 averaging perhaps 2300 fathoms. A second is, the ascertaining of the 

 temperature at different depths ; in some places in low latitudes the 

 deep-sea temperature is lower than in high latitudes. A third is, the 

 dredging up of Crustacea of new forms. A fourth is, the ascertaining 

 the character of the soft bottom of the Atlantic : this will probably 

 require the examination of the geologist. Dredgings made among the 

 banks of the New-England coast by Mr. Verrill have given results very 

 similar to those of Dr. Carpenter. The Congo expedition, fitted out, I 

 believe, by Mr. Young, and organized by the Eoyal Geographical Society, 

 was last heard of at some distance up the country, at a point on the 



