66 



A paper was read, entitled, " Experiments on the Length of the 

 Seconds' Pendulum ; made at the Royal Observatory at Greenwich." 

 By Captain Edward Sabine, of the Royal Regiment of Artillery, 

 F.RS. 



The experiments described in this paper were made with the 

 original convertible pendulum constructed by Capt. Kater, and em- 

 ployed by the author in Portland Place, in the year 1817; except that 

 the tail pieces were removed, and the moveable weight dispensed 

 with : and they were made on the vacuum apparatus established in 

 the south-west angle of the Pendulum-room, the place assigned for 

 it b}^ the Astronomer Royal. Having had reason to suspect that the 

 retardation of the vibrations of the pendulum performed in circular 

 arcs, when the weight was above, was greater than that assigned by 

 the formula commonly employed, the author first investigates the 

 correction necessary to be applied from this cause. He next as- 

 certains the reduction to a vacuum for the small residue of air 

 which the apparatus still contained, or for the small portion which 

 may have introduced itself by leakage. The alteration of rate for 

 each degree of Fahrenheit is then determined to be 0.441, a quan- 

 tity almost exactly the same as that which was deduced from a 

 former inquiry. The result of the present inquiry is, that the vibra- 

 tions of Captain Kater's pendulum, which at 57° were found to be 

 86069. 1 , are at 62°, 86066.9. At this latter temperature, the length 

 of the seconds pendulum, in vacuo, would be 39.13734? inches. 

 Tabular details of the experiments accompany the paper. 



A paper was read, " On recrossed Vision ; being the Description 

 of a distinct Tribe of ocular Phenomena, supplementary to a Rati- 

 onale of the Laws of cerebral Vision, recently published." By John 

 Fearn, Esq. Communicated by Captain John Grover, F.R.S. 



The phenomena described in this paper, and which the author 

 designates those of recrossed vision, are cases in which objects placed 

 between and very near the eye, such as the two sides of the nose, 

 appear on opposite sides of the sphere of vision : the object on the 

 right side of the nose being seen to the left by the right eye, and 

 that which is on the left of the nose being seen to the right by the 

 left eye. These and other phenomena illustrative of the well-known 

 law by which we estimate the position of objects with relation to 

 the eye to be in a line drawn from its image in the retina through 

 the centre of the eye, are considered by the author as requiring 

 further explanation. Not satisfied with the theory of Berkeley, that 

 the mind is guided by the perceptions received from the sense of 

 touch, in interpreting the signs furnished us by the sight, the author 

 proposes to explain these phenomena by an hypothesis of his own, 

 which he states in the following words. " Over and above the gift 

 of two external or cranial eyes, man has been by his adorable 

 Creator endowed with an internal cerebral organ, which performs 

 the office of a third eye, by being the common recipient of impres- 

 sions propagated either from one, or both of the external eyes ; and 

 the mind, in her chamber of percipience, steers with regard to ex- 



