Читать книгу A Practical Manual of the Collodion Process. Giving in Detail a Method For Producing Positive and Negative Pictures on Glass and Paper онлайн

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LIGHT, HEAT, AND ACTINISM.

A sunbeam may be capable of three divisions—light, heat, and actinism; the last causes all the chemical changes, and is the acting power upon surfaces prepared to receive the photographic image. The accompanying illustration, ssss1, will readily bring to the minds of the reader the relation of these one to another, and their intensities in the different parts of a decomposed sunbeam.

Fig. 2.

The various points of the solar spectrum are represented in the order in which they occur between A and B, this exhibits the limits of the Newtonian spectrum, corresponding with ssss1. Sir John Herschel and Seebeck have shown that there exists, beyond the violet, a faint violet light, or rather a lavender, to b, which gradually becomes colorless; similarly, red light exists beyond the assigned limits of the red ray to a. The greatest amount of actinic power is shown at E opposite the violet; hence this color "exerts" the greatest amount of influence in the formation of the photographic image.