An Experimental Study of Latent-Image Formation by Means of Interrupted and Herschel Exposures at Low TemperatureMeasurements of Reciprocity Law Failure at Low Temperature*

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Abstract
The present paper contains results of experiments carried out to test the theory of latent-image formation recently proposed by Gurney and Mott. In their theory, these authors have introduced the concept of electrolytic transport of Ag+ ions to account for the nucleation of latent image Ag about the sensitivity specks preexistent on the surface of the grains. The Ag+ ions are supposed to diffuse to the specks under the attraction of electrons trapped there during the exposure to light. The first experiment consisted of a series of intermittent exposures made at liquid air temperature with warm-up periods between flashes. The results indicate that something vital to the photographic process takes place during the warm-up period between exposures. The second experiment consisted of a series of Herschel exposures made under the following temperature conditions: (a) White-light exposure 20°C, Herschel exposure 20°C; (b) white-light exposure 20°C, Herschel exposure −186°C; (c) white-light exposure −186°C, Herschel exposure 20°C; (d) white-light and Herschel exposures both at −186°C; (e) case (d) repeated with warm-up period between the exposures. The results obtained are radically different under the different conditions. Finally, results are presented on reciprocity measurements at temperatures 20°C, −78°C, and −186°C. These results show that the low-intensity reciprocity law failure has disappeared at −78°C and that the high intensity failure has practically disappeared at −186°C. All of the foregoing results are shown to have ready interpretation on the Gurney-Mott picture of latent-image formation.

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