THE HISTORY OF SOMK DISCOVKRIES OF PIIOTOCR M'll V. 2U1 



aloii.i; llio whole Iciiirtli of (lie plate from liclow and on tlic side (.ppositc the 

 coatiii;,'. When the liiiuid has ceased to run. the plate is dried in the darl<. 'I'he 

 eoatinj,' heinj; well (h-ied it is to he jilaeed in tlie camera (.hscnra. The time 

 reiiuired to lu-ocure a photographic copy of a landscaite is from seven to ei^dit 

 hours, hut sin.<,'le monuments strom;I.v ilhmiinatcd Iiy tlic sun oi- \ci-.\ l.riixht in 

 tliemselves are cojiied in al)out ilww liours. 



Wlien ojierating on jjlass It is necessary, in order to increase tiie litrlit, to 

 ]>lace the phite upon a piece of jiaper, with yreat care that the coimection is 

 perfect over every part, as otiierwise confusion is produced in the design hy 

 i mperf ect reflection. 



It frecniently happens th;it wlien the i)late is removed from tlie camera tliere 

 is uo trace of any imajre upon its surface. It is tlierefore necessary to use an- 

 other process to hrinj; out the liidden desifjn. 



To do this, i)rovide a tin vessel larger than the tahlet, havinj? all around a 

 ledge or horder ;">() nun. (2 Knglisli inches) in depth. Let this he three- 

 fourths full of th(> oil of petroleum. Fix your tahlet hy the hack to n piece of 

 wood which completely covers the vessel and place it so that the tahlet, face 

 downwards, is o^-er but- not touchiui,' the oil. The vai)or of tiie petroleum pene- 

 trates the coatins of the plate in those parts on whicli the li.i,dit has acted 

 feehly — that is. in the portions which correspond to the shadows — imparting to 

 them a transparency as if notliing were tliere. On tlie contr:iry. tlie points of 

 the resinous coating on which light has acted, having l)een rendered imjiervious 

 to the vapor, remain unchanged. 



The design must he examined from time to tinu' and withdrawn as soon as 

 a vigorous effect is obtained. By urging the action too far even the strongest 

 lights will be attacked by the vapor and disapi)ear. to the destruction of the 

 jiiece. 



It nni}^ perhaps appear to .some that I have needlessly given the 

 particulars of a process, now superseded by others, possessing the 

 most infinite sensibility, j)rodii('ing in a few minutes a better effect 

 than was obtained by the heliographic process in several hours. 

 There are, however, so many curious facts connected witli the action 

 of light on these resins that no treatise on photography could l)e 

 considered complete without some description of thein: and this 

 process is now revived with a view to the i)r()(luction of etchings 

 directly from nature. 



M. Daguerre remarks that numerous experiments tried bv him 

 with these resinous preparations of M. Niepce j)rove that bglit can 

 not fall upon a body without leaving traces of decomposition; and 

 they also demonstrate that these bodies possess the power of renewing 

 in darkness what has been lost by luminous action, jn-ovided total 

 decomposition has not been effected. This henograi)hic jirocess nnist 

 be regarded as the earliest successful atl(iii|)l at lixing on solid tablets 

 the images of the camera obscura and at dexcloping a doiinant image. 



B. Talbot's Piionxiioxic Dkawinmjs. 



On tlie 81st of January, 18:51), six ntonths prior to the j^ublication of 

 M.' Daguerre 's process, Mr. Fox Talbot connniuiicated to the Royal 

 Society his photographic discoveries, and in February he gave to the 



