PHOTOGRAPHY, APPLICATIONS OF.—The introduction of the modern dry-plate process, and consequently the reduction of the time of exposure to fractions of a second, has caused photography to be of great and wonderful assistance to nearly all the modern arts and sciences. Perhaps the science that has mostly benefited has been astronomy.
may be easily, explained. The sensitiveness of the eye is very limited. A star placed at such a distance that with the most powerful telescope we possess it is still imper ceptible,will always remain invisible, but with the photographic camera it is different. By greatly prolonging the exposure, this tiny invisible ray of light slowly but surely acts upon the sensitive plate, and after a sufficient length of time (it may require hours) it reveals its image. When we glance up at the heavens on a starry night we see some thousands of stars visible to the naked eye ; with the assistance of a powerful telescope we see thousands more, but by exposing a photo graphic dry plate for some length of time we become aware of the existence of many hundreds more of these heavenly bodies, more appearing the longer the plate is exposed. The chemical plate possesses two principal aavantages over tne eye. .t'irst it is sensitive to rays utterly power less to produce any visual effect, and next it can accumulate impressions almost indefinitely, it being possible to photograph objects so faint as to be perfectly hidden from our vision. By this means only may we eventually learn whether a blank space in the sky truly represents the end of the stellar universe, or whether farther and farther still, worlds shine beyond veiled in the obscur ity of immeasurable distance. Photographs of the stars were made as early as 1850 by Whipple, of Boston, and since then many thousands have been made of every region of the heavens. A complete chart is now being undertaken. For this purpose about 14,000 plates will have to be exposed from all parts of the earth, and these plates will be so arranged that when correctly placed they will form a complete map.
Some idea of the increased astronomical knowledge that has been gained by the aid of photography may be had from the fact that in Cygnus 170 stars had been carefully mapped out by the old laborious process. A photograph made recently revealed the existence of over 7,000 stars. With regard to lunar and solar photography our astronomers have not been behind. A solar Daguerreotype was made at Paris as early as 1845. In 1857 De la Rue was commissioned by the Royal Society to construct an instrument specially for photographing the sun at Kew Observatory. This instrument was used to make solar pictures or photographic records of the solar condition, and was continued for over fourteen years. For some time it has been asserted that the spots on the sun have a regulating effect upon this earth. Dr. Zeyer, of Prague, claims that by means of photographs of these solar spots he is able to predict by more than twenty-four hours the approach of tempests, hurricanes, earthquakes, etc. The transit of Venus, comets,
nebula, eclipses, etc , have all received the attention of the camera. See Astronomical Photo graphy.
Medicine. The physician is gradually recognizing the claims of photography to his atten tion. He is now able to photograph the eye by a flash of light so that the pupil, being previously in the dark, is dilated to its utmost, and has no time to contract before the deed is done and the image permanently recorded. Cameras are now being constructed for photographing the interior of the abdomen.* Valuable photographs, too, have been made of peculiar diseases, natural phe nomena, etc., which cannot but be of great use to the medical student.
In Chemistry, photography has been of service in registering the belted zones of the spec trum, and making images of these bands, parts of which are invisible to the eye, and by this means not only can we obtain some information regarding the constitution of stars and nebula, but also some idea respecting the relative motions of these bodies and our earth.
Military science of warfare has also been aided by the art of photog raphy. Balloons and kites are now constructed capable of carrying a camera with which photo graphs can be made of the surrounding country, the position of the enemy, strength of their fortifications, etc.
For mapping and surveying this arrangement would also be of great use.
In Meteorology photography assists by giving permanent records of the dark nimbus and the bright rolling cumulus clouds. The lightning flash is clearly shown as it really is. Further, it helps the meteorologist by registering for him the rising and falling of the barometer and thermometer.
In Microscopy we are able to photograph the disease-bearing generations of bacteria, vibrio and schizomycetes, and to throw these photographs on a screen so that the image of the little flea assumes the proportions of the gigantic elephant.
Indeed, the uses of photography are many. It has been used to send letters from besieged cities to anxious friends and relatives outside. It has served to photograph the action of the tor pedo in throwing up the water, and to give truthful records of the field of battle. It helps the clever engineer by multiplying his plans and by giving him evidence of work done above or below the ground, determining the depths of the sea, and the directions of currents. It serves to keep in the hands of justice the image of the villainous murderer, or the avaricious forger. It detects the spurious banknote, and assists the expert in his tests of handwriting. No traveler's equip ment is complete nowadays unless it contains a set of photographic apparatus, enabling him to bring back from his travels pictures of the curious things that he has seen, and the picturesque places that he has visited.
These are a few among the many things which photography does for mankind. Every year shows some fresh use for it, and it is difficult to say where it will end, if end it will.