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 176 AGASSIZ been widely felt, producing similar phenomena over other portions of the earth's surface ; that the north of Europe must have been at the same time covered with a similar sheet of ice. Agassiz first announced his glacial theory in a discourse delivered before the Helvetic society in 1837; but in order to investigate the facts more thoroughly, he first visited most of the Alpine glaciers, and then established his head- quarters on the glacier of the Aar, where for eight consecutive summers he continued the researches which formed so large a part of his scientific labors in Europe. These researches are embodied in two works. The first, entitled J&tudes sur les glaciers, published in 1840, with plates, contains a description of the glacial phenomena and a statement of the author's views of their former extent. The second, published at Paris in 1847, under the title of Systeme glaciaire, contains an account of the investigations made during "his last five visits, 1841-'45, upon the mode of progress of the glaciers, and is accompanied by plates and a topographical chart. An excellent and graphic account of these visits and researches is given in a little work by his companion, Mr. Edward Desor, Excursions et sejours de M. Agassiz et de ses compagnons de voyage dans les glaciers et les hautes regions des Alpes. Since his resi- dence in the United States, Professor Agassiz has occupied himself with investigations of the distribution of the bowlders and the smooth surface of beds of rock over the North Amer- ican continent, which he also attributes to the action of glaciers, extending from the north. The results of these investigations are chiefly recorded in the volume containing an account of an excursion to Lake Superior. From 1846 the biography of Mr. Agassiz belongs to the scientific history of the United States. In the autumn of that year he arrived in Boston, from Paris. The object of his visit was, in the first place, to make 'himself familiar with the natural history and geology of this country, in fulfilment of a mission suggested to the king of Prussia by Alexander von Humboldt, and in the second place to meet an invitation from Mr. John Amory Lowell to deliver a course of lectures in Boston. Eighteen months or two years had been allotted to the first task, and ample means were provided by the Prussian government for that purpose. Soon after his arrival in Boston Prof. Agassiz delivered his first course of Lowell lectures, consisting of a general review of the animal kingdom. These lectures were listened to by audiences of 1,500 to 2,000 hearers, embracing all that was most cultivated in science and letters in the society of Boston and the vicinity. Immediately after- ward, by special request, he delivered another course upon the glaciers and the phenomena connected with their former greater extension. Having completed these labors, he visited New York, Philadelphia, and Charleston, to com- pare the animals of the northern shores with those of the more southern latitudes of this continent. On his return to the north early in the summer of 1847, he met with Prof. A. D. Bache, superintendent of the United States coast survey. Mr. Bache invited him to avail himself of the facilities presented by the oper- ations of the coast survey for the further pros- ecution of his researches. The offer was so liberal and of such importance in a scientific point of view, that Agassiz could hardly credit his good fortune ; and upon being assured that he might without difficulty visit at will every point of the coast in the well-equipped coast survey vessels, he exclaimed that this would decide him to remain to the end of his days in the United States. He spent part of the sum- mer of 1847 on board the Bibb, commanded by Capt. C. H. Davis, on the coast of Nantuck- et and Martha's Vineyard. The immediate re- sult of this, and a second cruise along the same coast, was several papers upon the medusoe of Massachusetts, and upon a coral found near Holmes's Hole. In the same summer he vis- ited, in company with Mr. J. A. Lowell, Niag- 'ara falls and the White Mountains. During the next three winters he delivered courses of lectures before the Lowell institute upon com- parative embryology and the successive devel- opment of the animal kingdom. At the close of 1847 Mr. Abbot Lawrence founded the scientific school in Cambridge, and a professor- ship of zoology and geology was offered Mr. Agassiz, which he accepted, after having ob- tained from his government an honorable dis- charge. He entered upon his duties in Cam- bridge in the spring of 1848, and at the close of the academic year started with 12 of his pupils upon a scientific exploration of the shores of Lake Superior. The results of this journey are contained in the volume entitled "Lake Superior," the narrative part of which was written by Mr. J. Eliot Cabot, together with the reports of the lectures the professor delivered at the close of each day. Dr. J. Le Conte contributed the account of the coleop- tera. In 1848, in conjunction with Dr. A. A. Gould, he published "Principles of ZoSlogy," for the use of schools and colleges. From that period Prof. Agassiz has devoted his time alter- nately to teaching and making original investi- gations. Besides his university lectures he has delivered in the winters courses of lectures in different parts of the country, while exploring its natural history. In these excursions he has been accompanied by assistants, and the col- lections he has made are the most complete ex- tant, embracing the whole range of the animal kingdom. In this manner he has traversed the country from Lake Superior to the gulf of Mex- ico, and from the Atlantic coast to the valley of the Mississippi, delivering courses of lectures in Savannah, Mobile, New Orleans, St. Louis, Cincinnati, and many other places, besides those already mentioned. In 1850 he spent the winter upon the reef of Florida, in the service of the coast survey, ascertaining the mode of growth and the direction of the in-