354 PROCEEDINGS: PHII^OSOPHICAI, SOCIETY 



also, the resultant speed along that course, or the total time required 

 for making a flight. 



Conditions of pressure and wind that would be favorable for eastward 

 and westward flights along the two routes are briefly discussed, and 

 tables are given showing the average number of days, monthly, seasonal 

 and annual, that are favorable for such flights. The figures in these 

 tables are based upon an examination of daily marine weather maps 

 covering a period of ten years. The results of this study show : (a) at 

 an altitude of 500 to 1000 meters conditions are favorable for an eastward 

 trip approximately one-third of the time, the percentage being slightly 

 greater along the northern than along the southern route ; (6) at greater 

 altitudes the percentage of favorable days materially increases, es- 

 pecially along the northern route; (c) for the westward trip the per- 

 centage of favorable days is so small as to make trans-Atlantic flight in 

 this direction impracticable until the cruising radius of air-craft is 

 increased to such an extent that they are relatively independent of wind 

 conditions; (d) there is little choice as to season, for, although the pre- 

 vailing westerlies are stronger in winter than in summer, yet, on the 

 other hand, stormy conditions are more prevalent in winter, the net 

 result being about an equal percentage of favorable days in the two 

 seasons. The transition seasons, spring and autumn, show a slightly 

 smaller percentage than do summer and winter. For full publication 

 of this paper see Monthly Weather Review, February, 191 9. 



Discussion: The paper was discussed by Messrs. BowiE, Aul,t, 

 Humphreys, Brooks, and Hazard. 



Mr. C. F. Marvin presented the second paper on The flight of aircraft 

 and the deflective influence of the earth's rotation. The paper was illus- 

 trated by charts. 



Abstract: Objects moving freely in a horizontal manner over the 

 earth's surface are deflected constantly to the right in the Northern 

 hemisphere by a force which at airplane speeds, say 40 meters per sec- 

 ond, and at latitude 50 degrees, amounts to .447 dynes per gram of 

 moving matter. 



The purpose of the paper was to indicate the amount by which an 

 aircraft flying in still air may be carried off any desired course by the 

 action of this small force, especially when a compass is the only guide 

 followed in holding the course. 



The speaker showed that a residual or resultant force, in addition to 

 the deflective influence, almost constantly exists in assumed straight- 

 away flying and arises from the reactions between the airplane and the 

 air. The pilot has no knowledge of or control over this force, which, 

 nevertheless, dominates the flight and operates to turn the machine 

 from its course, now to the right, now to the left, in an irregular and 

 entirely accidental manner. Repeated rectifications of the course are 

 necessary, and it was assumed for purpose of quantitative analysis that 

 on the average the pilot rectifies the course every 60 seconds of the 

 flight. 



