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SCIENCE 



[N. S. Vol. L. No. 1282 



plish. the flight, the interest ui the meteorolog- 

 ical aspects became more manifest. And when 

 aviators intending to fly across the Atlantic 

 had to wait many weeks for favorable weather, 

 the importance of the meteorological condi- 

 tions became recognized as paramount. 



" Trans- Atlantic flight from a meteorolo- 

 gist's point of view," was discussed in detail 

 by Mr. W. R. Gregg, of the Weather Bureau, 

 at a meeting of the Philosophical Society of 

 Washington, March 29, 1919; and this paper 

 was published widely during the first half of 

 May.^ In the selection of routes for trans- 

 Atlantic flight, helpful winds as well as geo- 

 graphical distance must be considered. Thus, 

 the best eastward routes are Newfoundland to 

 Ireland and Newfoundland to the Azores and 

 Portugal ; while the best westward routes, so 

 far as wind aid is concerned, are (1) Scotland 

 to Labrador via Iceland and Greenland, (2) 

 Portugal to the West Indies, and (3) Africa 

 near Gape Verde, to eastern Brazil. Since 

 eastward flight from Newfoundland offers the 

 best initial possibilities for airplanes, Mr. 

 Gregg confined his discussion to the weather 

 conditions in the middle latitudes of the 

 North Atlantic. 



The temperatures in winter or summer are 

 usually not extreme. The moisture of the air 

 over the oceans is of importance only in its 

 connection with fogginess, cloudiness and pre- 

 cipitation. The average cloudiness along the 

 more northern route (Newfoundland to Ire- 

 land) is about 70 per cent., but this includes 

 the thick fogs as well as the clouds. Fortu- 

 nately, the aviator can generally rise above 

 the clouds for observation, and over the sea, 

 it is not so dangerous to fly below low clouds 

 as it is over the land. Rainfall occurs very 

 frequently, i. e., on about two thirds of the 

 days — but, here again, it is possible for the 

 aviator to fly high and thus to avoid the 

 heaviest rain. Pog, while a grave danger in 

 trying to land, or in flying low, usually does 

 not extend high. On the Grand Banks fogs 

 occur on about 60 per cent, of the days in 

 summer and 20 to 35 per cent, of those in 



1 See Monthly Weather Review, 1919, Vol. 47, 

 pp. 65-75. 



winter; on the Irish coast the percentages are 

 10 and 5, respectively. Since these fogs do 

 not usually extend very far inland, they 

 seldom would prevent landing. The vertical 

 extent of the Newfoimdland fogs is almost 

 always less than 250 meters, and so can easily 

 be left below the flier at the start. 



The general pressure distribution and winds 

 favor eastward flight, though the frequency of 

 gales is unfavorable, gales occurring on about 

 25 per cent, of the days in winter and 5 in 

 summer on the Newfoundland to Ireland 

 route, and slightly less often on the New- 

 foundland to the Azores and Portugal route. 

 Tropical cyclones, fortunately, are rare. The 

 conditions in the free air are not very differ- 

 ent from those on the surface, for over the 

 ocean the wind increases and turns but little 

 with altitude, the surface friction being very 

 small relative to that over the land. 



While the average conditions are generally 

 favorable for eastward flight in middle lati- 

 tudes across the North Atlantic, the actual 

 conditions at a particular time are those 

 which must be encountered. The problem, 

 then, is to choose a day on which the winds 

 will be most favorable. Mr. Gregg chose from 

 among the daily weather maps of the North 

 Atlantic on file at the Weather Bureau, May 

 29, 1906, as a day which would have been a 

 good one for a start. By interpolating 

 weather maps at two-hour intervals he com- 

 puted for eight divisions of a flight from 

 Newfoundland to Ireland, the direction and 

 velocities of the " gradient " winds, and from 

 these the proper bearings of an airplane's 

 course which would carry it to Ireland with 

 the aid of the wind, in the shortest possible 

 time. He computed not only the bearing of 

 the course, but also the direction in which the 

 airplane would have to move relative to the 

 air in order to maintain the necessary bearing 

 for the stipulated distances of each part of 

 the course. On May 29-30, 1906, an airplane 

 with an air-speed of 90 mi./hr. could have 

 made the flight in 17 hours, whereas in a calm 

 20 hours would have been necessary. 



With the aid of Messrs. Tingley and Pater- 

 son of the marine division of the Weather 



