DAGUERROTYPE. 



and the decided terms in which Sir Humphrey Davy 

 expresses his failure might perhaps have discourage d, 

 his less experienced follower, had he not fortunately 

 already conquered the difficulty which had de- 

 stroyed the hopes of the former chemists. 



" In the course of my experiments directed to 

 that end," says Mr Talbot, " I have been as- 

 tonished at the variety of effects which I have 

 found produced by a very limited number of dif- 

 ferent processes when combined in various ways ; 

 and also at the length of time which sometimes 

 elapses before the full effect of these manifests it- 

 self with certainty. For I have found that images 

 formed in this manner, which have appeared in 

 good preservation at the end of twelve months 

 from their formation, have nevertheless somewhat 

 altered during the second year." He was induced 

 from this circumstance to watch more closely the 

 progress of this change, fearing that in process of 

 time all his pictures might be found to deteriorate ; 

 this however was not the case, and several have 

 withstood the action of the light for more than 

 five years. 



The images obtained by Talbot's process are 

 themselves white, but the ground is differently 

 and agreeably coloured; and by slightly varying 

 the proportions, and some trifling details of mani- 

 pulation, any of the following colours were readi- 

 ly obtained : light blue, yellow, pink, brown, 

 black, and a dark green nearly approaching to 

 black. 



The first objects to which the process was ap- 

 plied were leaves and flowers, which it rendered 

 with extraordinary fidelity, representing even the 

 veins and minute hairs with which they were 

 covered, and which were frequently imperceptible 

 without the aid of a microscope. Mr Talbot goes 

 on to mention that the following considerations led 

 him to conceive the possibility of discovering a 

 preservative process. Nitrate of silver, which has 

 become darkened by exposure to the light, is no 

 longer the same chemical substance as before ; 

 therefore, if chemical re-agents be applied to a pic- 

 ture obtained in the manner already mentioned, 

 the darkened parts will be acted upon in a differ- 

 ent manner from those which retain their original 

 colour, and after such action they will probably be 

 no longer affected by the rays of the sun, or, at 

 all events, will have no tendency to assimilate by 

 such exposure; and if they remain dissimilar, the 

 picture will continue distinct, and .the great diffi- 

 culty be overcome. 



The first trials of the inventor to destroy ths 

 susceptibility of the metallic oxide were entirely 

 abortive ; but he at length succeeded to an ex- 

 tent equal to his most sanguine expectations. The 

 paper employed by Mr Talbot is superfine writing 

 paper: this is dipped into a weak solution of com. 

 mon salt, and dried with a towel till the salt is 

 evenly distributed over the surface : a solution of 

 nitrate of silver is then laid over one side of the 

 paper, and the whole is dried by the heat of the 

 fire. It is however necessary to ascertain by ex- 

 periment the exact degree of strength requisite in 

 both the ingredients, for if the salt predominates, 

 the sensibility of the paper gradually diminishes, 

 in proportion to this excess, till the effect almost 

 entirely disappears. 



In endeavouring to remedy this evil, Mr Talbot 

 discovered that a renewed application of the nitrate 

 not only obviated the difficulty, but rendered the 

 preparation more sensitive than ever ; and by a repe- 



tition of the same process the mutability of the 

 paper will increase to such a degree, as to darken 

 of itself without exposure to the light. This 

 shows that the attempt has been carried too far, 

 and the object of the experimentalist must be to 

 approach, without attaining this condition. Hav- 

 ing prepared the paper and taken the sketch, the 

 next object is to render it permanent, by destroy- 

 ing the susceptibility of the ingredients for this 

 purpose. Mr Talbot tried ammonia and several 

 other re-agents with little success, till the iodide of 

 potassium, greatly diluted, gave the desired result : 

 this liquid, when applied to the drawing, produces 

 an iodide of silver, a substance insensible to the 

 action of light. This is the only method of pre- 

 serving the picture in its original tints, but it re- 

 quires considerable nicety, and an easier mode is 

 sufficient for ordinary purposes. It consists in im- 

 mersing the picture in a strong solution of salt, 

 wiping off the superfluous moisture, and drying it 

 by the heat of the fire ; on exposure to the sun, 

 the white parts become of a pale lilac, which is 

 permanent and immovable. Numerous experi- 

 ments have shown the inventor that the depths of 

 these tints depends on the strength of the solution 

 of salt ; he also mentions that those prepared by 

 iodine become a bright yellow under the influence 

 of heat, and regain their original colour on cool- 

 ing. Without the application of one of these pre- 

 servatives the image will disappear by the action 

 of the sun ; but if inclosed in a portfolio, will be 

 in no danger of alteration : this, Mr Talbot re- 

 marks, will render it extremely convenient to the 

 traveller, who may take a copy of any object he 

 desires, and apply the preservative at his leisure. 

 In this respect Mr Talbot's system has the advan- 

 tage over that of M. Daguerre, since it would be 

 scarcely possible for a traveller to burden himself 

 with a number of metallic plates, which in the lat- 

 ter process are indispensable. 



Since the publication of the above discoveries, 

 numerous candidates have appeared in the field, all 

 claiming the palm of originality, while philosophers 

 of every grade and country have eagerly pursued 

 the investigation of the subject. The first we 

 shall notice is M. Niepce, who claims priority even 

 over M. Daguerre ; and the account he publishes, 

 if correct, will undoubtedly determine the question 

 in his favour. A letter from M. Bauer is the prin- 

 cipal evidence for M. Niepce, who, it appears, men- 

 tioned his discovery to this gentleman in the year 

 1827, while on a visit at Kevv, and by the advice 

 of his friend he drew up a memoir on the subject, 

 and caused it to be forwarded to the royal society. 

 This document was however returned, it being con- 

 trary to the rules of the association to receive ac- 

 counts of scientific discoveries unless they detailed 

 the process employed. M. Niepce shortly after- 

 wards returned to France, having presented to his 

 friend several specimens of the newly discovered 

 art, which are still in the possession of M. Bauer. 

 The pictures taken are of two kinds, copies from 

 engravings, and copies from nature ; the best of 

 the former is in the possession of Mr Cussel, and 

 is considered nearly equal to those of M. Daguerre, 

 with suitable allowance for twelve years' exposure; 

 the specimen taken from nature is however by no 

 means so successful, and is considered inferior to 

 the earliest attempts of his countryman. M. 

 Bauer distinctly asserts that he possessed copies 

 of engravings produced solely by the action of light, 

 which were capable of being Multiplied in the 



