The Calotype paper is sensitive to light to an extraordinary degree, which transcends a hundred times or more than of any kind of photographic paper hitherto described. This may be made manifest by the following experiment: take a piece of this paper, and having covered half of it, expose the other half to daylight for the space of one second in dark cloudy weather in winter. This brief moment suffices to produce a strong impression upon the paper. But the impression is latent and invisible, and its existence would not be suspected by anyone who was not forewarned of it by previous experiments.