A Manual Of Photography

190 PRACTICE OF PHOTOGRAPHY. to the truth. The form of experiment was to select a number of specimens of paper.—prepare them with great care in precisely the same manner, and expose them to the same solar influences. They were partly covered with a piece of colourless glass,—the object of this being to determine whether under it the action was gulelver or slower than when exposed uncovered. Sir John Herschel has shown that there are some peculiar differences in this respect ; and this method offered a very correct mode of determining the relative effects. I.—Papers prepared with Muriate of Soda and Nitrate of Silver. a. Superfine satin post.... Considerable exalting effect. b. Thick wove post ......Depressing influence. c. Superfine demy........Slight exalting effect. d. Batli drawing card .... Changes slowly. e. Thick post............Slight exalting effect. f. Common bank post.... Ditto. g. Thin post ............Very tardy. h. Tissue paper..........Considerable exalting effect. II.—Papers prepared with Muriate of Barytes and Nitrate of Silver. a. Superfine satin post.... b. Thick wove post .... c. Superfine demy....... d. Bath drawing card .... e. Thick post........... /. Common bank post .... g. Thin post........... h. Tissue paper........ Slight exalting influence. Ditto, but stronger. Similar to a. Similar to a. Considerable exalting influence. Similar to a. Similar to e. Results uncertain. III.—Papers prepared with Muriate of Ammonia and Nitrate of Silver. a. Superfine satin post.... b. Thick wove post....... c. Superfine demy........ d. Bath drawing card e. Thick post............ f. Common bank post.... g. Thin post............. h. Tissue paper.......... Strong exalting influence. Results uncertain—dependent on the size employed. Slight exalting effect. Results uncertain. Ditto. Very slow. Ditto. Strong exalting influence.