June 13, 1919] 



SCIENCE 



559 



total eclipse of unusual duration, which, at maii- 

 mum, may amount to six minutes and fifty seconds. 



The eclipse track is rather unfortunately situ- 

 ated. Beginning in the Pacific Ocean, just off the 

 coast of Peru, it sweeps across South America, tra- 

 versing the Bolirian Mountains, the forests of 

 Brazil, and the higher lands of the eastern coast. 

 Then it crosses the Atlantic, almost along the 

 equator, just grazes the southern coast of the 

 great western projection of Africa, passes tempo- 

 rarily out to sea again, and crosses the main part 

 of the dark continent by way of the Congo basin 

 and Lake Tanganyika — finally leAving the earth's 

 surface at a point in the Indian Ocean not far 

 from the African coast. 



The region within which a partial eclipse is vis- 

 ible extends far northward and southward, includ- 

 ing practically all of South America except the 

 extreme southern trip, and all of Africa except 

 the Mediterranean coast. The region where total- 

 ity is longest lies in the Atlantic, and the maximum 

 duration of eclipse obser\-able from land stations is 

 about four minutes, which is reached on the east 

 coast of South America and the west coast of 

 Africa. There is, to be sure, one small island in 

 the Atlantic, lying almost in the central line of 

 totality, where the eclipse lasts fully six minutes; 

 but as this spot, known as St. Paul's Eocks, con- 

 sists of a few jagged rocks rising to a height of 

 60 feet from deep water, with no anchorage and no 

 fresh water, it is hardly an inviting station for 

 even the hardiest astronomer, in spite of the fact 

 that certain optimistic souls have nominated it as 

 a way station for transatlantic airplane flights. 



The climatic conditions along most of the track 

 are unfavorable — ^the best chances of fine weather 

 being on the high lands back of the eastern coast 

 of Brazil, and in central Africa above Tanganyika. 

 On account of the remoteness of these stations, 

 and of the disorganization resulting from the war, 

 few expeditions appear to be projected to view 

 the eclipse. One English and one or two American 

 parties, however, are likely to make the journey. 



MAPPING FROM THE AIR 



Requests made to the United States Geolog- 

 ical Survey, Department of the Interior, for 

 information concerning: the possibilities of 

 photographic surveying from airplanes or other 

 aircraft have recently become so numerous 

 that it is deemed necessary to issue a state- 

 ment on this subject. For two years the United 

 States Geological Survey, which prepares and 



publishes more maps than any other organiza- 

 tion in the world, has devoted much time and 

 labor to the study of problems to be solved in 

 photo-aerial surveying. The camera has long 

 been used in survej'S on the ground, and the 

 Geological Surrey has been making studies to 

 determine the best methods of using it in 

 aerial work. Before the war the jianoramic 

 camera was employed by the Geological Sur- 

 vey for mapping in Alaska, and it had been 

 widely used for photographic surveying in 

 Canada and in EuroiJe. Aerial photographic 

 surveying involves no new jwinciples, yet it 

 differs essentially from jihotographic survey- 

 ing on the ground, for the line of view from a 

 camera in a balloon or an airplane is vertical, 

 not horizontal. A complete statement of the 

 Geological Survey's investigations in photo- 

 graphic mapping from the air will later be 

 prepared for publication. 



The problem of photographic surveying from 

 the air is dominantly an engineering problem. 

 Photographic technique is of course an essen- 

 tial part of the work, but it is a subordinate 

 part, for the best photographs are valueless as 

 map-making material unless they are accom- 

 panied by the requisite engineering data. Pro- 

 jections, adjustments, and other details of 

 map-making technique are as necessary in 

 photo-aerial sun-eying as in other surveying, 

 and all map-making work should therefore be 

 the work of exix^rienced engineers. 



Photogn*aphic mapping from aircraft is en- 

 tirely practicable but it has not yet been 

 brought to the point where it can supersede 

 ground surveying. The science of cartography 

 will no doubt be greatly advanced wlien the 

 aerial method is perfected, but fundamental 

 problems remain to be solved, and this fact 

 should be recognized and all possible energy 

 should be devoted to the solution of those prob- 

 lems. It is hoped that solutions of the essen- 

 tial problems in photo-aerial surveying will 

 soon be obtained, and that this method will be 

 put to practical use in map-making. 



FIFTH NATIONAL EXPOSITION OF CHEMICAL 

 INDUSTRIES 



The Fifth Annual National Exposition of 

 Chemical Industries will be held this year in 



