Page:Collier's New Encyclopedia v. 09.djvu/524

LEFT TflANSFOBMISM 462 T-RANSIT INSTRUMENT concomitant physiological modification; (2) a process of change in the condition of the earth's surface. TRANSFUSION OF BLOOD, a surgi- cal operation by which blood is conveyed directly from the body of one person to that of another. The earliest case of transfusion of blood on record is that of Pope Innocent VIII., who was unsuccess- fully operated on in April, 1492. Various experiments were afterward made by Wren and Lower in the transfusion of blood from one animal to another, and by Denys of Montpellier in injecting the blood of calves into human subjects; but the experiments were not attended with any great success, so that the operation fell into desuetude. It was not till about the year 1824, when Dr. Blundell pub- lished his work on "Physiological and Pathological Researches," that the trans- fusion of blood was regarded as a legiti- mate operation in obstetric surgery; and at the present day the operation is chiefly restricted to cases of profuse hemorrhage in connection with labor, though it is sometimes practiced in cases of sudden and profuse hemorrhage from other causes. The operation is best performed by taking blood, instantly before injec- tion, from the arm of a healthy person; but Dr. Brown-Sequard showed that the blood of various animals can be used in- discriminately, provided only certain pre- cautions be taken; and Professor Panum made the important discovery that de- fibrinated blood is in every respect as well suited for the operation as pure blood. TRANSIT, in astronomy, the passage of a heavenly body over the meridian. Also the passage of one of the inferior planets, Mercury or Venus, over the sun's disk. Mercury being so near the sun, and so difficult to observe with accuracy, its transits are not nearly so important to astronomers as those of Venus. In 1716 Dr. Halley published a paper in the "Philosophical Transactions," advising that the transits of Venus over the sun's disk which would occur in A. D. 1761 and 1769 should be taken advantage of for the purpose of ascertaining the sun's distance from the earth. Though he was dead long before these dates arrived, the government of the day acted on his sug- gestion. In 1769 the celebrated Captain Cook was sent to Otaheite for the pur- pose of noting the transit, another ob- server being dispatched to Lapland. The observations of the latter being erroneous the distance of the sun was exaggerated by about three millions of miles. In 1874, when the next transit occurred, all civil- ized nations sent out scientific men to observe it. It was known that it would be invisible at Greenwich, but expeditions were sent out by the British Government to the Sandwich Islands, to New Zealand, Egypt, Rodriguez, and Kerguelen Island. Other nations occupied other stations, and the weather proved suitable at most places for accurate observation. Transits of Venus come, after long in- tervals, in pairs, eight years apart; and another transit took place on the after- noon of Dec. 6, 1882. In the British Isles the weather was generally unfavorable, clouds with occasional snowflakes obscur- ing the sky at Greenwich, and through nearly all Great Britain, except on the W. coast. At Dublin, partial observa- tions were obtained ; and of various Brit- ish expeditions sent abroad complete suc- cess was obtained in Madagascar and at the Cape of Good Hope. Observers from the United States and other countries were also successful. The observation of the distance the planet moves to the right and left of the sun, in describing its orbit, enables an astronomer to ascertain the relative distance of the two luminaries. The relative breadth of the sun's diame- ter as compared with his distance from the earth is also easily ascertained. If, then, two observers on the surface of our sphere take their stations at ju- diciously selected points, as widely apart as possible, and note a transit of Venus, the planet will have a lesser line to traverse at the one place than the other, and will do it in a shorter time. From accurate notation of the difference in time taken in connection with the dif- ference in length it is possible to calcu- late, first the breadth of the sun and secondly his distance from the earth. When the materials obtained in connec- tion with the two transits were worked out, it was found, as Hansen had sus- pected, that the sun's distance had been over-estimated, and it was reduced from 95,300,000 to 92,700,000 miles.^ In engineering, a portable instrument resembling a theodolite, designed for measuring both horizontal and vertical angles. It is provided with horizontal and vertical graduated circles, one or two levels, and a compass, and is mounted upon a tripod-stand. TRANSIT INSTRUMENT, an instru- ment designed accurately to denote the time when a heavenly body passes the meridian. It consists of a telescope sup- ported on a horizontal axis, or pivots, the extremities of which terminate in cylindrical trunnions resting in metallic supports shaped like the upper part of the letter Y, and hence termed the "Y's," and imbedded in two stone pillars. In