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Rh often interfere with the awards of justice; but here, more than anywhere else, errors of personality are eliminated by the impersonal tribunal to which all questions are at last referred. A pretty definite idea is conveyed, when it is said that a man has "mastered a science." He must have made himself familiar with a certain body of facts and principles, with their historic growth and their degree of development. But the familiarity here implied is not that which is current in the walks of literature. It is not to be gained merely by reading. It implies a direct knowledge of the phenomena themselves—knowledge at first hand—and the exactions in this sphere of thought go further still. A man cannot be said to have mastered a science until he has thoroughly possessed himself of its method of research, and proved this thoroughness by successful, original work. He must have contributed to its advancement, to its original stock of observations and inductions, and done it so effectually that those who stand highest shall recognize the validity and value of his work. This condition being complied with, the number of sciences that have been successfully pursued, and the degree of their complexity, become fair measures of the mental breadth, grasp, and power of the minds engaged upon them. Humboldt was preeminent because of his conquest of many sciences. Helmholtz has a high place in European science because he is confessedly strong in mathematics, physics, and physiology, and has combined the researches of these sciences in carrying on his original investigations. Judged by this standard, the subject of the present sketch must be assigned an eminent position in American science, as he is an acknowledged master in the three extensive departments of mineralogy, geology, and zoology, having made original investigations of great value in all these fields of study.

Prof. was born, in 1813, in Utica, New York, where he passed the first years of his life. He seems to have had an early inclination to the sciences, as at seventeen years of age he entered Yale College, attracted by the fame of Prof. Silliman (Sr.), the distinguished pioneer in American science. During the regular course of study at New Haven, Mr. Dana evinced an especial love for the natural sciences, without neglecting philological and mathematical pursuits, in the latter of which he was distinguished. He was graduated with honor, Bachelor of Arts, in 1833, and about the same time received the appointment of teacher of mathematics to midshipmen in the Navy of the United States. In that capacity, he sailed to the Mediterranean, in the United States ship-of-the-line Delaware, returning in 1835. During the two years following, he acted at Yale College as assistant to the distinguished professor whose successor in office he afterward became.

In December, 1836, he was appointed mineralogist and geologist of the Exploring Expedition then about to be sent by the Government of the United States to the Southern and Pacific Oceans. The five