Page:Collier's New Encyclopedia v. 04.djvu/506

LEFT GYNiECOLOGY 434 GYROSCOPE GYNECOLOGY (jin-e-kol'o-ji or gi- ne-), that branch of medicine which treats of the diseases of women. GYPSEOUS SERIES, in geology, the lower freshwater limestone and marl constituting the Upper beds of the Middle Eocene in the vicinity of Paris, France. They are of white and green marls with subordinate beds of gypsum. At the Hill of Montmartre is a quarry of gypsum valuable for the manufacture of plaster of Paris. Splendid fossil re- mains of Eocene mammals have been found in it. Similar gypseous marls are worked for gypsum at St. Romain, on the right bank of the Allier. GYPSUM, calcium sulphate crystal- lized with two molecules of water Ca- So4*2H20. It is often found by the decom- position of pyrites when lime is present. Gypsum calcined is called plaster of Paris, and is used for taking casts of statues. Gypsum is used as a manure; it facilitates the decomposition of rocks containing alkaline silicates. Technically gypsum is regarded as a mineral deposit, in some places constitut- ing rock masses. It may be of any age. Near Paris it is Middle Eocene. Frapoli eays that some gypsums were originally carbonates instead of sulphates of lime, and that they underwent metamorphism by the action of volcanic sulphurous or Bulphurohydrous vapors. The produc- tion of gypsum in the United States in 1919 was about 3,430,000 short tons, valued at about $16,000,000. GYPSY MOTH, the Bombyx dispar an insect abounding in central Europe, where it does much damage to trees. Linnaeus was the first to describe it. The eggs are laid in August and hatch in the spring in the trunks of trees, and on rocks and fences, the caterpillars feeding on plants and trees. After a few months the caterpillars, having attained their full growth, pupate, the moths emerging from the cocoon some weeks after. The insect was brought to America by Leo- pold Trouvelot, who was experimenting at Medford, Mass., with silkworms, and the specimens escaped. Twenty years later the damage caused by the cater- pillars attracted public notice, and since that time, despite public measures taken to cope with the ravage, the gypsy moth has become a pest in many localities in Massachusetts. An effort was made by the Massachusetts State Board of Agri- culture to exterminate the insect, and was carried on over a period of ten years, at an expenditure of over a mil- lion dollars. The work was not thorough, however, and in recent years the pres- ence of the moth has become so notice- able that public measures have had to be resumed to counteract the injury to plants, shrubs, and trees caused by it. The Massachusetts Board of Agricul- ture has issued bulletins giving the re- sults of the methods originated by it, and, in so far as these methods have been followed by the various municipali- ties that have been obliged to deal with the insect, they have borne fruit. GYROGONITE (ji-rog'5-mt), the sporangium, or seed-vessel, of the flower- less plant-genus Chara. It is very rough and hard, consisting of a membranous nut, covered by an integument, both of which are spirally streaked or ribbed. The integument is composed of fine spiral valves of a quadrangular form. GYROSCOPE (jir'o), an instrument constructed by M. Foucault, to make the rotation of the earth visible. The prin- ciple on which it proceeds is this — that, unless gravity intervenue, a rotating body will not alter the direction in which its permanent axis points. In the gyro- scope there is a rotating jnetallic disk, the middle point of whose axis is also the center of gravity of the machine. By this GYROSCOPE A. Gyroscope. B. Gyroscope as used in torpedo. device the action of gravity is eliminated. The instrument, moreover, is so con- structed that the axis of rotation can be made to point to some star in the sky. Then, as the heavy disk whirls round, it is found that the axis continues to point to the moving star, though, in conse- quence of this, apparently altering its direction relatively to bodies on the earth. If, again, the axis be pointed to the celestial pole, which is fixed, no alteration in its position relative to bodies on the earth takes place. The only fea- sible explanation of these appearances is that the earth is revolving on its axis. The gyroscope has been a valuable ad- junct as a stabilizer in the making of aeroplanes.