66 GENERAL VIEW AND BASIS OF SCIENTIFIC RESEARCH. 



time by simply breathing upon them. Other organic 

 solids besides brain, which^also grow and decay, per- 

 petuate impressions ; for instance, the seed of plants and 

 animals. Physiology supplies many instances of actions 

 analogous in some degree to memory ; the effect of small- 

 pox inoculation is an example. ' If, on a cold polished 

 piece of metal, any object, as a wafer, is laid, and the 

 metal then be breathed upon, and, when the moisture 

 has had time to disappear, the wafer be thrown off, though 

 now upon the polished surface the most critical inspection 

 can discover no trace of any form, if we breathe upon 

 it, a spectral figure of the wafer comes into view, and this 

 may be repeated again and again. Nay, even more ; if 

 the polished metal be carefully put aside where nothing 

 can deteriorate its surface, and be so kept for many 

 months, even for a year, on breathing again upon it, the 

 shadowy form emerges ; or, if a sheet of paper, on which a 

 key or other object is laid, be carried for a few moments 

 into the sunshine and then instantaneously viewed in the 

 dark, the key being simultaneously removed, a fading 

 spectre of the key on the paper will be seen ; and if the 

 paper be put away where nothing can disturb it, and so 

 kept for many months, at the end thereof, if it be carried 

 into a dark place and laid on a piece of hot metal, the 

 spectre of the key will come forth. In the cases of bodies 

 more highly phosphorescent than paper, the spectres of 

 many different objects which may have been in succession 

 laid originally thereupon, will, on warming, emerge in 

 their proper order. 



These illustrations show how trivial are the physical 

 expressions which may be thus registered and preserved. 

 A shadow is said never to fall upon a wall without leaving 

 thereupon its permanent trace, a trace which might be 

 made visible by resorting to proper processes. All kinds 



