Royal Society. 221 



resulting spectrum, however, were not always synchronous portions, 

 sometimes appearing and disappearing by separate or partial changes, 

 like the effect of the dissolving views of the magic lantern. 



6. Pictures, diagrams, printing, &c., were found, under due influ- 

 ence of light, to yield cognizable and sometimes vivid impressions 

 on the retina. Diagrams in black and white, or chequered surfaces 

 like that of a chess-l)oard, gave very distinct pictures, always nega- 

 tive, the squares coming successively into view, beginning with the 

 portion gazed at. The succession of changes, when the impression 

 was strong, in this experiment was not a little curious, the perfect 

 image of the chess-board after bursting into view, gradually fading 

 altogether away, and then reviving, in less strong tints, in a series 

 of repetitions. 



Another curious, though anticipated result, the author also de- 

 scribes under this section, — the determination, by viewing the ocular 

 spectra, of portions of diagrams or elements in pictorial or typogra- 

 phical surfaces, which had not been noticed in the act of gazing. 

 Thus, particularly on viewing a line of printed figures at a particular 

 point, without noticing those on either side, a considerable series, 

 right and left, were so plainly depicted on the visual organ as to be 

 easily known ; whilst, in like manner, a point in a line of a printed 

 placard being gazed at, the lines above and below came into view on 

 closing the eyes, and could frequently be read. 



Of certain general facts elicited by this first series of investigations, 

 the author notices, that in viewing impressions on the retina with 

 closed eyes, all the pictures appear to occupy a jiosition externally, 

 similar to the effect when the objects are directly seen ; that the 

 spectra derived from moderate or strong degrees of transmitted light 

 have prevalently the character of transparency, and those from very 

 low degrees, most ordinarily, of opacity ; that although many of tiie 

 spectral phsenomenathe author had observed were well known to be 

 capable of elicitation in the ordinary form of the experiment with 

 the eyes open, yet the series of phaenomena, as a whole, could not 

 be so elicited, nor was it possible by such form of exjaeriment to 

 analyse and compare the pha?nomena whilst in progress of change, 

 which, in the form he had adopted, were usually exhibited as plainly 

 as if the spectra were the real and immediate effects of ordinary 

 direct vision ; and that such is the precision and such the cer- 

 tainty with which the jiictures are ordinarily developed, after duly 

 viewing any illuminated object, that the expected result, so far as the 

 eliciting of definite pictures is concerned, hardly ever fails. 



Jan. 12, 1854.— The Lord Chief Baron, V.P., in the Chair. 



A paper was read, entitled " On some New and Simple Methods 

 of detecting Manganese in Natural and Artificial Compounds, and 

 of obtaining its Combinations for oeconomical or other uses." By 

 Edmund Davy, Esq., F.R.S., M.R.I.A. &c. 



In this pajjcr the growing importance of manganese since its 

 discovery, and its extensive distribution in Nature are noticed. 

 Manganese is chiefly found combined with oxygen, but its oxides 



