National Geographic : 1906 Nov
VOL. XVII, No. rI WASHINGTON NOVEMBER, 1906 THI® J. NATIlONL _L M AMA ZIINIE _ THE AMERICAN ECLIPSE EXPEDITION* By REAR ADMIRAL COLBY M. CHESTER, U.S.N., RETIRED FORMERLY SUPERINTENDENT OF THE U. S . NAVAL OBSERVATORY AND COM MANDER-IN-CHIEF OF THE AMERICAN ECLIPSE EXPEDITION OF 1905 THE American Eclipse Expedition of 1905 was the largest one that was ever fitted out by any na tion, and I have had difficulty in gleaning from the mass of scientific data resulting from its work a gist of the matter which in a popular form I shall endeavor to place before you tonight. In studying the records of parties who had observed eclipses of the sun, it be came evident to me that the larger the number of instruments and observers that could be put into the field the better was the chance for procuring results, provided the observers were properly educated for the work. It also appeared that the military training of a man-of-war's crew gave them many of the qualities required for the observers, who were to take ad vantage of the important few moments during which the sun can be eclipsed, and I endeavored to procure as many men to select from as possible. This assumption was strongly fortified by the experience of Sir Norman Lockyer, the distinguished astrophysicist of England, who has writ ten extensively of his association on eclipse work with the British navy. In the navy men are trained for years to prepare for the one important battle, pos- sibly of a lifetime, which may last but for a few brief moments, and yet the results of which may make or ruin a nation. The importance of training for this event can not therefore be overestimated. Likewise an eclipse of the sun can cover but a short period of time, and but few of such events which can be properly observed occur in any one man's profes sional experience. It is necesary, then, to make thorough preparations if we would get from these rare occasions the full benefits which may be derived from them. HOW ECLIPSES ARE CAUSED It is hardly necessary to go into the theory of eclipses with this audience to make clear the operations undertaken by the eclipse expedition of 1905, and with out being didactical I will simply explain why we go so far as Spain to observe a total eclipse of the sun. It is well known that an eclipse of the sun is caused by the moon passing in its orbit between that body and the only known people from whom its view can be shut out. Now the sun is about four hun dred times as far away from our in habited globe as is the moon. By an in- : An address to the National Geographic Society, March 30, 1906.