Celluloid Film Research Articles

The Use of Negative Paper

Dr. Bromley gave a brief account of the use of negative paper for radiographic work. He said that he had been using negative paper for radiography for about a year, and within its limitations he could say that he was thoroughly satisfied with it. It was identical with the negative films which many professional photographers used for portrait work. Its limitations could be overcome to some extent by the use of an intensifying screen. The essential thing was to use a soft tube. He had never worked with a tube above 60,000 volts, and his senior radiographer used one which was softer still. The usual five minutes' development was given. The speaker passed round a few examples obtained in ordinary hospital work. He pointed out that the smallest fractures of the carpal and metacarpal bones could be detected; also very fine detail in the patella and in the elbow joint. The prints exhibited covered a wide range of work. The chief advantage of the method was its cheapness as compared with the use of celluloid film...

Absorption of Ultrasonic Waves by Various Gases

Absorption coefficient for ultrasonic waves in C${\mathrm{O}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{H}}_{2}$ and He.---A beam of ultrasonic waves with a frequency of 612 kilocycles from an oscillating quartz crystal was passed through a mixture of gas and air, contained in a brass absorption tube with ends covered by thin celluloid films. The design of the tube greatly reduced the effect of resonance and allowed the use of two different lengths of absorbing gas, leaving the geometrical arrangement of openings and absorbing screens the same. The emergent beam was allowed to fall upon another quartz crystal which had a natural frequency very nearly equal to the frequency of the waves and which was connected to the grid of a triode. The intensity of the received signal was measured by a previously calibrated vacuum tube voltmeter. A logarithmic decrease in the transmitted energy with increase in the percentage of the gas in the mixture was found with C${\mathrm{O}}_{2}$, ${\mathrm{N}}_{2}$O, ${\mathrm{H}}_{2}$, and He. The increase in the absorption coefficient (${\mathrm{cm}}^{\ensuremath{-}1}$) at 612 kilocycles when air was replaced by a mixture containing 1 percent by volume of the gas was found for C${\mathrm{O}}_{2}$ to be 0.029; for ${\mathrm{N}}_{2}$O, 0.034, for ${\mathrm{H}}_{2}$, 0.014, for He, 0.0025. For argon mixtures no absorption was observed.Reflection of ultrasonic wave by a thin celluloid film. The fractional part of the beam which was transmitted by the films at the ends of the absorption tube, increased with increase in percentage of C${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$O but decreased with increase in percentage of ${\mathrm{H}}_{2}$ and He, agreeing qualitatively with Rayleigh's theory.

Diffraction of Cathode Rays by a Thin Film

IF a fine beam of homogeneous cathode rays is sent nearly normally through a thin celluloid film (of the order 3 × 106 cm. thick) and then received on a photographic plate 10 cm. away and parallel to the film, we find that the central spot formed by the undeflected rays is surrounded by rings, recalling in appearance the haloes formed by mist round the sun. A photograph so obtained is reproduced (Fig. 1). If the density of the plate is measured by a photometer at a number of points along a radius, and the intensity of the rays at these points found by using the characteristic blackening curve of the plate (see Phil. Mag., vol. 1, p. 963, 1926), the rings appear as humps on the intensity-distance curves. In this way rings can be detected which may not be obvious to direct inspection. With rays of about 13,000 volts two rings have been found inside the obvious one. Traces have been found of a fourth ring in other photographs, but not more than three have been found on any one exposure. This is probably due to the limited range of intensity within which photometric measurements are feasible.

Absorption in the Region of Soft X-Rays

Energy of soft x-rays from a tungsten-coated nickel target as a function of potential from 40 to 610 v---Soft x-rays from the target were allowed to fall on a solid solution consisting of CaS${\mathrm{O}}_{4}$+2 percent MnS${\mathrm{O}}_{4}$. The square of the time of duration of the thermoluminescence produced was assumed to be proportional to the total energy of the x-rays. The results indicate that in the range 40-610 v., the total energy varies approximately as the square of the potential applied to the tube.Absorption of soft x-rays (40-610 v.) by thin celluloid films.---By interposing a thin celluloid film, about 25 m\ensuremath{\mu} thick, between the target and the thermoluminescent substance, the transmission of the film was measured for various values of the applied potential from 40 to 610 volts. The transmission varied from 0.0 percent at 40 volts (minimum wave-length 310A) to 57 percent at 610 volts (minimum wave-length 20A). The results are in general agreement with the hypothesis that the absorption varies as the cube of the wave-length, that K absorption discontinuities in celluloid occur between 300 and 600 volts and that the x-rays cover a wide spectral region. A photographic method of investigating absorption is also described. The results are fairly consistent with those obtained otherwise but the method suffers from the fact that the photographic plate is not equally sensitive to energy of different wave-lengths.Absorption of soft x-rays (300-600 v.) in air and ${\mathrm{H}}_{2}$.---Computation based on previous measurements give for air values of $\frac{\ensuremath{\mu}}{\ensuremath{\rho}}=6.0, 6.25, 7.0, 7.6\ifmmode\times\else\texttimes\fi{}{10}^{3}$ at 600, 500, 400, and 300 volts respectively. These figures agree fairly well with those given by Holweck in ${\mathrm{O}}_{2}$ and ${\mathrm{N}}_{2}$. For ${\mathrm{H}}_{2}$ the value of $\frac{\ensuremath{\mu}}{\ensuremath{\rho}}$ is calculated to be about 1.8\ifmmode\times\else\texttimes\fi{}${10}^{4}$ which is larger than the value given by Holweck and larger than is to be expected from the results for air.

Societies and Academies

LONDON. Optical Society, October 15.—C. V. Raman and Sushil Krishna Datta: On Brewster's bands. The paper considers the explanation of Brewster's bands and other allied phenomena from the viewpoint proposed by Schuster (Phil. Mag., Oct. 1924). When monochromatic light is reflected by or transmitted through two parallel plates in succession, a superposition of the Haidinger ring-systems due to the two plates is obtained. When non-homogeneous light is used, the Haidinger rings disappear and also the superposition pattern, except in the special case of the differential system of the first order for two plates of equal thickness. A simple geometrical explanation is thus forthcoming why Brewster's bands can be observed even in non-homogeneous light with thick plates in this case.—T. Smith: Lagrange's theorem and stationary functions. Lagrange's theorem for several variables is expressed in a concise notation and used to evaluate a function which is stationary for small changes in each of its variables.——W. G. Collins: Some new instruments for recording rapidly varying phenomena. In these instruments a fine stylus terminating in a highly polished spherical surface of small radius rests on a travelling strip of transparent celluloid. A record of the movement of the part of the instrument to which the stylus is fixed is obtained by the permanent deformation of the surface of the celluloid by the stylus. As this deformation is produced by very slight pressure and no material is removed from the celluloid, the energy required to produce the record is very small. Only a comparatively small amount of celluloid film is required, and the record is immediately available for examination by optical methods.

Radiographs by Fluorescent Screens

PERHAPS some of your readers who are practising electrography are not aware that those of them who possess a potassium platino-cyanide screen can diminish their exposures to a quarter of the time now necessary. I tried the experiment yesterday, and have been more than pleased with the results. The modus operandi is as follows. The screen is first laid on the darkroom table, platino-cyanide uppermost. A celluloid rapid sensitive film is then placed upon it, gelatine side downwards, and in contact with platino-cyanide. Upon the top of all is placed the hand or other object to be electrographed, and in contact with the celluloid. The whole, including screen, celluloid film, and object, are then raised from the table, and a light tight cloth bag drawn over them and properly secured. This arrangement, exposed under the Crookes' tube in the usual way, gives about four times the speed attainable without the reinforcing action of the screen. The “grain” of the screen shows; but if the salt has been finely powdered before preparing it, this is no great objection. Glass-sensitive plates are of course inadmissible.

The Röntgen Rays

So many people are buying tubes for the “new photography,” that I think it ought to be made known that the best results can be obtained with the original spherical tube used by Prof. Crookes in 1879, to show the incandescence of platinum under impact of the projected molecules which were focussed on it by a concave kathode. I have been using such a tube for my best work up to now. On January 29 last, I put in hand a larger tube of the same kind, with the same large concave kathode at the top and small disc anode at the bottom, but without the platinum in the middle. This tube is six inches in diameter. But the tube-makers have been so occupied with smaller tubes, which are far less trouble to make, that it was only sent me yesterday. I at once used it to photograph a man's hand on an inverted celluloid film, the whole enclosed in a black bag in the usual way. With five inches of spark, and an exposure of three minutes at eight inches distance from the film, I obtained fine definition of the bones as far as the film went, including the junction of the two bones of the arm with the wrist. No Tesla apparatus was used. Had it been, doubtless the exposure could have been considerably shortened. An area of twelve inches by ten inches was covered perfectly. The tube was then set on for thirty minutes without stopping with a ten-inch spark coil, and showed no perceptible heating.

Phosphograms

IF a glass plate (or a celluloid film) is evenly coated with phosphorescent calcium sulphide in a suitable menstruum, and then exposed for a few minutes in a photographic camera, a phosphorescent negative can be taken of a sunlit view. When this plate is carefully applied to an ordinary photographic film for a short period in the dark room, on developing the latter a reversed negative (or phosphogram as I prefer to call it) of the original picture is permanently produced. If the picture consists (as in my case) of a vista of smoke-stained chimney-pots, the slated roofs and stuccoed walls of adjacent houses, the negative, under favourable circumstances, will show considerable traces of natural colours. In the case of phosphorescent calcium sulphide, which glows with a beautiful purple violet light, it is not difficult to understand why it acts on the gelatine film so readily as it does. Both the phosphorescent rays and the most active photo-chemical rays belong (as is well known) to the most refrangible rays of the solar spectrum; that the one should thus react on the other is not surprising.