The mathematicians have also their culte, dating back to Bowditch, the translator of the "Mecanique celeste," and the author of a work on practical navigation. He died in Boston, where they are now erecting a magnificent monument to his memory. Mr. Peirce, professor at Cambridge, is considered here the equal of our great mathematicians. It is not for me, who cannot do a sum in addition, to pretend to a judgment in the matter.* (* Though Agassiz was no mathematician, and Peirce no naturalist, they soon found that their intellectual aims were the same, and they became very close friends.) You are familiar, no doubt, with the works of Captain Wilkes and the report of his journey around the world. His charts are much praised. The charts of the coasts and harbors of the United States, made under the direction of Dr. Bache and published at government expense, are admirable. The reports of Captain Fremont concerning his travels are also most interesting and instructive; to botanists especially so, on account of the scientific notes accompanying them. I will not speak at length of my own work,--my letter is already too long. During the winter I have been chiefly occupied in making collections of fishes and birds, and also of the various woods. The forests here differ greatly from ours in the same latitude. I have even observed that they resemble astonishingly the forests of the Molasse epoch, and the analogy is heightened by that between the animals of this country and those of the eastern coasts of Asia as compared with those of the Molasse, such as the chelydras, andreas, etc. I will send a report upon this to M. Brongniart as soon as I have the time to prepare it. On the erratic phenomena, also, I have made numerous observations, which I am anxious to send to M. de Beaumont. These phenomena, so difficult of explanation with us, become still more complicated here, both on account of their contact with the sea and of the vast stretches of flat country over which they extend.