TICKNOR 390 TIDE bar in 1813. In 1815 he embarked for Europe, and visited the chief capitals for the purpose of pursuing his studies. On his return in 1820 he was appointed Pro- fessor of Modem Languages and Litera- ture in Harvard University. In 1835 he resigned his professorship, and for the next three years traveled in Europe with his family. In 1849 he published a "His- tory of Spanish Literature" (3 vols. 8vo, New York), corrected and enlarged edi- tions being subsequently published. It was at once recognized by scholars as a work of value, and has been translated into Spanish and German. He produced in 1863 "The Life of William Hickling Prescott," the historian, with whom he had maintained a close friendship. He died in Boston, Jan. 26, 1871. TICONDEROGA, a village in Essex CO., N. Y.; on Lake Champlain, and on the Rutland and the Delaware and Hud- son River railroads; 90 miles N. of Al- bany. Here is the outlet of Lake George which falls 150 feet in 1^/^ miles and affords excellent water iK)wer. It has manufactories of machinery, paint, air engines, graphite, blank books, pulp, paper, etc., and an assessed property valuation of about $800,000. Ticon- deroga figured prominently during the Colonial and Revolutionary periods. In 1755 the French erected a fort here and named it Carrillon. Two years later Montcalm started from this place with 9,000 men and captured Fort William Henry on Lake George. In 1758 General Abercrombie endeavored to take the French fort, and was repulsed after losing 2,000 men; but in 1759 it fell into the hands of General Amherst together with Crown Point. Both were then en- larged and strengthened at a heavy ex- pense. In 1775 the works were taken by Ethan Allen while weakly garrisoned. Two years later the fort surrendered to General Burgoyne, and after being dis- mantled was abandoned. Pop. (1910) 2,475; (1920) 2,102. TIDE, a regular periodic oscillation to which the surface of the sea at any place is subject. The oscillation takes place about twice a day, the periodic time being, on an average, about 12 hours and 26 minutes. Consequently if high tide occurs at noon one day, it will occur next day some 50 minutes later. This is pre- cisely the interval of time which elapses between two successive meridian pas- sages of the moon; and that there must be some connection between the tides and our satellite was early recognized by astronomers. The explanation, however, was lacking till Nevrton proved them to be a necessary conspauence of the law of gravitation. The phenomenon of the tide is, indeed, a case of perturbations, of exactly the same nature as the irregu- larities which the action of the sun pro- duces on the motions of the moon. If we compare the attraction of the moon on a particle of the earth's surface with the attraction exerted on the earth as a whole, we readily see that, accord- ing as the particle is on the nearer or further side of the earth, the former at- traction is greater or less than the lat- ter; and it is to this difference of attrac- tion, to which the waters yield, that the whole phenomenon of tide is due. The nearer waters are driven toward the moon, the further waters away from it. If the earth were spherical and uniform- ly covered with water, the tendency would be to make the water arrange itself in the form of a spheroid with the longer axis pointing toward the moon; and did the earth always present the same face to the moon, this would be rigorously the case. Such is the equilibrium theory of tides, as originally given by Newton. It ac- counts so far for the phenomena, such a3 the simultaneous existence of high water at places diametrically opposite, but does not even approximately correspond to the true state of affairs. Newton was fully aware of this, and indeed has given the solution of the problem on other and truer assumptions. If the hypothetical earth covered uniformly with water is rotating, so as to present each point of its surface successively to the moon, each particle of water will be moving with a certain momentum which will be suffer- ing retardation or acceleration according to its position relatively to the moon. The longer diameter of the water ellip- soid will consequently not point in the direction of the moon ; and the result will be the formation of two diametrically opposite waves, flowing round the earth in a direction contrary to its rotation. This is the kinetic theory, which forms the basis of Laplace's theory of tides. It also fails in practical application, since the continuity of the surface waters on the earth is very much broken by the distribution of land. More recently Young and Airy have approached the question as one of wave motion, basing their theory on the mo- tion of waves in canals. Until com- paratively recent times we have been regarding the moon as the sole tide- producing agent, but it is evident that the sun must have a similar action, though not so marked because of its much greater distance. It was proved by Newton that the disturbing forces exert- ed by two bodies on the same particle ar©
