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HISTORICAL SURVEY 21
The picture was fixed by plunging it in a solution of hypo-sulphite of soda.
The negative thus obtained is a picture on a plane surface of a solid object, and Talbot prepared positive pictures from negatives of this kind.
He placed the negative upon a piece of sensitized paper prepared with chloride of silver, as previously described, and allowed the light to act upon it. This shone through the white places of the negative, and imparted a dark colour to those parts of the sensitized paper lying under them, while the dark places of the negative protected the paper lying under them from the effects of the light. Thus he obtained a positive picture from a negative. He could repeat the process as often as he pleased, and therefore was in a position to prepare, by the aid of light, many positives from a single negative. Photography was thus classed among the arts that multiply copies, and this circumstance exercised an important result on its future development .
Daguerre's method only gave a single picture at a time ; if more were required, the person had to sit several times. In Talbot's method a single sitting sufficed to produce hundreds of pictures.
It must be admitted that the earlier pictures of the Talbot process were not remarkably engaging. Every roughness of the paper and each small speck of dirt were imprinted on the positive, which on this account could not be compared in point of delicacy with the fine daguerreotypes ; but the method was soon improved.
Experiments of Niepce de St Victor. — Niepce de St Victor, nephew of Nicophore Niepce, the friend of Daguerre, conceived the happy idea of substituting glass for paper in the preparation of the negative. He coated glass plates with a solution of albumen in which iodide of potassium was dissolved.
A solution of this kind can be easily prepared by