Page:The New International Encyclopædia 1st ed. v. 18.djvu/652

STEREOENITHES. 553 STERILIZED FOOD. em the contrary, ninny oi the species are not ratite at all. but carinate, one. at least, having been determined to be a vulture. The most con- sjiicuous genus is Phororhacos. See Bibd, Fos- sil. Consult NewtoUj Dictionary of Birds (New York, 1893-96). STEEEOSCOPE (from Gk. artptbi, stereos, solid + a-Koir£iv, skopein, to view). An optical instrument that enables one to see the pictures of objects not merely as plane representations, but with an appearance of solidity or relief. When a person looks at a solid body with both eyes the pictures formed on the retina of the two eyes are not alike, as the right eye is able to see more of the right side of the ob- ject and vice versa. When these two impres- sions are blended the object is seen with an appearance of depth or relief. It was not until 1838 that an attempt was made to produce this ettect. This was accomplished in the first stereoscope, which was devised by Wheatstone (q.v. ) and consisted of two plane mirrors at an angle of 90° and two similar clamps or supports for holding the picture. The face of the observer was placed close to the meet- ing point of the two mirrors and the light from each picture was reflected into the eye by the adjacent mirror. The pictures for use in this instrument were drawn as they would appear to each eye separately, and consequently were re- flected to the eyes as they would actually be seen. The apparatus was successful so long as the pictures were confined to representations of geometrical objects of three dimensions, which could be constructed readily, but the reproduc- tion of more complex objects, such as natural scenery, was beyond the skill of the artists, and it did' not occur to the inventor to use photog- raphy, which was then being developed. The stereoscope was brought to its present state by Sir David Brewster, who in 1849 constructed a lenticular stereoscope in which lenses were sub- stituted for the reflectors used by Wheatstone. Id this way he was able to obtain a magnified image as well as one characterized by the stereo- scopic effect. Instead of employing whole lenses he divided a double convex lens transversely into halves, which were placed in front of the two pictures with their thin edges adjacent. This was done so that the rays would be deviated by such an amount that they would apparently originate in a common point between the two pictures, the lens acting as a prism which always bends the rays around its base. In this way the two pictures, which are placed directly in front of the two lenses at a distance equivalent to the principal focus, are united into one image. The growth of photography and the ease with which pictures for the stereoscope could be produced soon made the instrument extremely popular, and the open form used in the United States was devised by Dr. Oliver Wendell Holmes, the poet. Brewster also invented a form of photo- graphic camera with two lenses to take stereo- scopic pictures. Instead of two lenses, which in modern stereoscopic cameras are gen- erally of the rapid rectilinear type, the position of the camera can be shifted, but the results are not as good as those obtained with two similar lenses mounted on a camera with a vertical par- tition which enables two pictures to be taken on the same plate. The lenses, generally speaking. should be about 2Vz inches apart, though a slight increase does not make any great difi'erence. the relief becoming more prominent. Too great a difi'erence. hciwevcr, makes an exaggerated and unnatural picture. In printing, the negative re- verses conditions, and tlie prints must be inter- changed, as the pictures taken on the right-hand side must always be seen with the right eye. The opera glass furnishes a familiar instance of the application of the binocular principle, and in the more modern double-tube telescopes and field glasses, particularly for military operations, great success has been attained in securing the stereoscopic effect with considerable magnifying power. Consult: Brewster, The Stereoscope (Leipzig, lS5(i) ; Helmholtz, Physiologische Op- tik (ib., 1856-66) ; Le Conte, Sight (New York, 1881); Mullfr-Pouillet, Lehrbuch der Physik (9th ed., Brunswick, 1897). STEREOTYPING. See Feinting. STERILITY (Lat. steriUtas, barrenness, from sterilis, barren; connected with Cik. arepebi, stereos, solid, stift", barren, aripiipoi, steriphos, hard, barren). Barrenness, infecundity. In a woman, sterility consists of an incapacity for conception; in a man, of the inability to procre- ate the species. T. G. Thomas, of New York, has analyzed exhaustively the cause of sterility in a woman as follows : ( 1 ) Causes preventing the entrance of semen into the uterus, including ab- sence of the uterus or vagina, obturator hymen, vaginismus, atresia vaginse, occlusion of cervical canal, conical shape of cervix, cervical endome- tritis, polypi or fibroids, displacements, very small OS internum or externum. (2) Causes pre- venting the production of a healthy ovule, in- cluding chronic ovaritis, cystic disease of both ovaries, cellulitis or peritonitis, absence of ovaries. (3) Causes preventing passage of ovule into uterus, including stricture or obliteration of Fallopian tubes, absence of Fallopian tubes, de- tachments and displacements of Fallopian tubes. (4) Causes destroying the vitality of semen or preventing fixation of impregnated ovum, in- cluding corporeal or cervical endometritis, mem- branous dysmenorrhea, menorrhagia or metror- rhagia, abnormal growths, areolar hyperplasia. Sterility in man is organic when there is anatomical derangement of the apparatus; atonic when erections are wanting or feeble; ancesthetic when there is a diminution of sensitiveness in the nerves supplying the male organ ; or psychic when mental conditions (as of fright, repulsion, etc.) inhibit the genital centre in the spinal cord. The determination of which partner in mar- riage is sterile is of great importance. In many countries obloqtiy and derision attach to the wife who fails to bear children, and her legal status is impaired. The woman is much less often to blame than has been stipposed. STERILIZED FOOD. Food that has been stibjected to au agent (usually heat) capable of destroying the germs of fermentation or disease which "may be present. The articles of diet which are not usually prepared by heat before ingestion, and ^vhich are capable of conveying disease, are fresh fruits and certain vegetables, water, and milk. Tlie two latter are particularly likely to act as carriers of patliogenie microorganisms. Water may be rendered sterile by boiling or by distilla- tion. It is then best kept for use in sterile bot-