THE PHOTOGRAPHING OF PATIENTS In the photographing of patients, the most difficult problem lies in obtaining sufficient light. It is frequently necessary to stop down the lens considerably as parts of the subject will be at different distances and the aim of the photographer is a large scale photograph with good detail in every part. Again the slight movement due to breathing, etc., will be sufficient to spoil the finest detail if the exposure is at all prolonged. Hence on both counts, the light must be powerful. Daylight is variable and often not available. In cases where the patient can be moved into a studio, the most serviceable source of artificial light is a battery of large gas-filled electric lamps. The light is under control, any special lighting can be repeated and the volume of light is virtually constant.
Record work in the wards of a hospital is often of extreme dif ficulty owing to the weakness of the light. Here a magnesium flash lamp enclosed in a fabric bag can often be used. The, exposure is practically instantaneous and the bag is afterwards removed and the smoke released outside the room. Care, however, should be taken not to use the apparatus when the slight explosion of the powder might cause distress.
When it is probable that a series of photographs will be required of a subject taken at certain intervals of time, it is most im portant that the conditions of lighting, position, etc., should not vary, so that the series may be comparable. Especially important is it that each photograph should be taken on the same scale. This is most readily ensured by measuring the distance from the front of the lens to the principal plane of the object and repeating this for the subsequent exposures.
To estimate the value of the degree of reduction, a clearly marked scale divided in feet or inches should be placed at the same distance from the lens as the principal plane of the object and in such a position that it is included in the photograph. The photograph of the scale is measured and the degree of reduction readily calculated.
With the object of making the records more comparative, it is of advantage to work with a series of standard reduction ratios, 1, etc. The distance lens-to-object is found for each ratio and then the camera placed at that distance and focussed. The lens for record medical work should be a long focus anas tigmat, capable of rendering the finest detail. Very big aperture lenses are seldom of much use in this work owing to their lack of depth of focus. The camera and stand should be rigid with a big range of adjustment. (B. D. H. W.) PHOTOGRAPHY, CELESTIAL. The invention of pho tography by Daguerre in 1839 led to a great step in astronom ical progress. The first application of the daguerreotype to the science was made by John William Draper of New York who photographed the moon on March 23, 184o, the exposure being 20 minutes. Experiments in the new method were made under the direction of W. C. and G. P. Bond at the Harvard college observatory, with the assistance of Messrs. Whipple and Black photographers of Boston, as operators, and the first photograph of the moon was taken there on Dec. 18, 1849, with the 15 in. object glass. A daguerreotype picture of the moon shown in London by George Bond at the Great Exhibition of 1851 attracted much attention.
Historical.—In England, Warren De la Rue, having seen the Harvard pictures, took up the subject and presented to the Royal Astronomical Society, in 1857, positive copies from a nega tive picture of the moon made by a collodion process that he had found practicable five years earlier. In 1864, Dr. Lewis Rutherford, of New York, made a telescope with object-glass of 11+ in. aperture so corrected as to bring the photographic rays to focus. About the same time Dr. Henry Draper excelled his father's efforts by taking photographs of the moon with a 15 in. reflector, and early experiments in lunar photography, among them those by Hartnup of Liverpool, should not pass unnoticed.