A Manual Of Photography

CHAPTER IV. ON THE PHOTOGRAPHIC REGISTRATION OF PHILOSOPHICAL IN- STRUMENTS AND THE MEANS OF DETERMINING THE VARIATIONS OF ACTINIC POWER, AND FOR EXPERIMENTS ON THE CHEMICAL FOCUS. Section I.—Photographic Registration. There are so many advantages attendant on self-registration, as to make the perfection of it a matter of much interest to every scientific enquirer. The first who suggested the use of pho- tographic paper for this purpose was Mr T. B. Jordan, who brought the subject before a committee of the Royal Cornwall Polytechnic Society, on the 18th of February, 1839, and exhi- bited some photographic registers on the 21st of March of the same year. The plan this gentleman adopted was to furnish each instrument with one or two cylinders containing scrolls of photographic paper. These cylinders are made to revolve slowly by a very simple connection with a clock, so as to gne the paper a progressive movement behind the index of the instrumen, the place of which is registered by the representation of its own image. The application of this principle to the barometer or thermo- meter is most simple ; the scale of either of these instruments being perforated, the paper is made to revolve as close as possible to the glass, in order to obtain a well-defined image. ihe cylinder being made to revolve on its axis once in forty-eight hours, the paper is divided into forty-eight parts by vertical lines, which are figured in correspondence with the hour at which they respectively arrive at the tubes of the instruments Ihe graduations on the paper correspond to those on the dial of the barometer or scale of the thermometer, and may be printed on the paper from a copperplate, or, what is much better, may be minted by the light at the same time from opaque lines on the winch WORM of course leave a light impression on the Dauer by this means we should have all that part of the paper above th/mercury darkened, which would at the same time be graduated with white lines, distinctly marking the fluctuations in its height for every minute during daylight, and noting the time of every passing cloud.