228 Royal Society :— 



It is probable that this reaction would produce the naphtlialamine 



term, corresponding to anilocyanic and cyanic acid. 



Cyanic acid. . .'. Cj H NOj 



Anilocyanic acid Cj4 Hg NO3 



Naphthocyanic acid jDja Hg NO^ 



Menaphthoximide, when heated, yields, in fact, a vapour of a most 



penetrating organic odour ; but Mr. Perkin has not yet obtained 



sufficient material for a more minute examination of the body to 



which it belongs. 



January 31. — The Lord Wrottesley, President, in the Chair. 



The following communication was read : — 



" Account of Pendulum Experiments undertaken in the Harton 

 Colliery for the purpose of determining the Mean Density of the 

 Earth." By G. B. Airy, Esq., Astronomer Royal. 



In the first section of this paper, the author explains the reasons, 

 founded on calculation, which appeared to make it probable that 

 the comparison of gravity at the top and the bottom of a mine 

 would give means of determining the earth's mean density with 

 accuracy, perhaps superior to that obtained in the Schehallien or the 

 Cavendish experiment ; and which induced him first in the summer 

 of 1826 (in concert with Dr. Whewell), and again in 1828 (with 

 Dr. Whewell, Mr. Sheepshanks and others), to try the experiment in 

 the Dolcoatli mine near Camborne in Cornwall. These attempts were 

 both frustrated by accidents having no connexion witli the essential 

 parts of the experiment. After a lapse of many years, he found that 

 several circumstances (of which one was the general familiarity with 

 the manipulation of the galvanic telegraph and the facility of applying 

 it to the comparison of widely separated clocks) were very favourable 

 to a repetition of the experiment ; and having selected the Ilarton 

 Colliery in the neighbourhood of South Shields as a fit place, in 

 which two stations could be found in exactly the same vertical but 

 at 1256 feet difference of height, and being assured of every assist- 

 ance from the owners of the mine, he proceeded with the experi- 

 ments in the months of September and October 1854. 



The principal instruments employed were two detached pen- 

 dulums on iron stands, the property of the Royal Society, which 

 were most carefully repaired by Mr. Simms ; graduated arcs, baro- 

 meters, thermometers, &c.; two clocks, one the property of the 

 Royal Society, which were fitted for this purpose with inclined 

 gilded reflectors upon the pendulum bobs, intended to be illuminated 

 by the light of lamps passing through holes in the side of the clock- 

 cases ; galvanometer-needles attached to the clock-cases, with circuit- 

 breakers ; a galvanic battery at the upper station ; a journeyman- 

 clock at the upper station, fitted with an apparatus by which it 

 completed the galvanic circuit at every 1 5^ of its own time ; and two 

 galvanic wires passing down the mine-shaft and forming a closed 

 circuit through the battery, the journeyman-clock, and the two 

 galvanometers. 

 . The working party consisted of Mr. Dunkin (superintendent) and 



