Royal Society, 455 



union of pictures, one of which is more or less turned round 

 in its own plane ; — to the phenomena exhibited by uniting the 

 images of two similar real solids, the one elevated and the 

 other depressed; — to the union of dissimilar plane figures 

 which should at the same time give a solid in relief, and in the 

 converse of relief*; — and to the union of portions of dissimilar 

 figures, those which are wanting in the one figure existing in 

 the other. Among the singular effects produced under these 

 various conditions, nothing is more remarkable than the ten- 

 dency or desire, as it were, of the eyes, to unite and fix the 

 two pictures hovering before them, to convert them into some 

 figure of three dimensions (sometimes in relief, sometimes in 

 the converse, and sometimes in both at the same time) ; and 

 the suddenness with which the two images start into union, 

 give birth to a solid figure on which the optic axes are con- 

 verged, and release the eyes from that unnatural condition in 

 which they had previously been placed. 



St. Leonard's College, St. Andrews, 

 January 1843. 



LXV. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 217.] 



Dec. 7? A PAPER was read, entitled, " On a sudden rise and 

 1843. ■* fall of the Sea in the Dock-yard Creek, Malta, on the 

 21st and 25th June, 1843." By S. Napier, Esq., Master- Attendant. 

 Communicated by the Lords Commissioners of the Admiralty. 



At 6 o'clock, a.m. on the 21st of June, the water was found to be 

 6 inches above the average height* and continued so till 6f , when it 

 rose to 18 inches, and in a few minutes sank to 3 feet 6 inches below 

 the average ; which oscillations continued till 8^ a.m., when it re- 

 sumed its usual level. On the 25th, a rise to the extent of 2 feet 6 

 inches above, followed by a fall of 3 feet below, the average, was 

 observed ; these alternations in height recurring four several times 

 on that day. The author was unable to assign any particular cause 

 for these extraordinary agitations of the sea. 



December 14. — A paper was read, entitled, " Researches into the 

 Structure and Development of a newly-discovered Parasitic Ani- 

 malcule of the Human Skin, the Entozoon folliculorum." By Eras- 

 mus Wilson, Esq., Lecturer on Anatomy and Physiology in the 

 Middlesex Hospital. Communicated by R. B. Todd, M.D., F.R.S. 



The animalcules which are the subject of this paper were disco- 

 vered above a year ago by Dr. Simon, who published a description 

 of their structure in the number of Muller's ' Archiv,' &c. for June 



* In order to produce simultaneously this double effect, the lines of the 

 pyramid, for example, which are to give the converse of relief, should be 

 fainter than the other lines, or in different and feebler colours. 



