544 SCIENCE PROGRESS. 



was called, resembled a Venetian blind in structure, being 

 constructed of a number of laths at a small distance one 

 above the other and driven by an engine working a pro- 

 peller. Although the machine was never allowed to fly, 

 being constantly held attached to a whirling table, it rose 

 from the little circular track on which it ran, and the lifting 

 power of the planes was found to be considerably greater 

 than that of a single wide plane of the same area. Phillips 

 had made elaborate experiments on wide planes before 

 coming to his present conclusions. 



Although there are some difficulties in adopting the 

 Venetian blind form to "soaring" experiments, the ad- 

 vantages arising from the use of narrow superposed planes 

 are generally admitted by engineers, and they have been 

 introduced in modified forms with considerable success. 



Where however the wing surface is required to be of 

 any considerable width from back to front, curved surfaces 

 are better than plane ones, as I now hope to explain. 



When an inclined plane surface is moving in a hori- 

 zontal direction or is acted on by a horizontal wind, the 

 total pressure is perpendicular to the surface, and by the 

 elementary laws of mechanics we can resolve this force into 

 two components, viz., an upward force, called the /z/? (which 

 /i/fs or supports the weight of the plane), and a horizontal 

 force called the dri/^ (which represents the force with which 

 the plane must be didveii). By decreasing the angle of incli- 

 nation of the plane to the horizon, we decrease the drift, but 

 if the plane is perfectly horizontal, the wind will exert no 

 pressure on it, so there will be no lift or drift at all. If, 

 however, instead of using a plane surface, a concave curved 

 surface of the same area is experimented with, it is found 

 that greater lift and less drift are obtained, so that it is 

 possible to support the same weight with less expenditure 

 of power than before. This result holds good provided 

 that the curved surface is inclined at a moderately small 

 anole to the horizon. When its inclination to the horizon 

 is considerable, the reverse is the case ; there is greater 

 drift and less lift than with the plane surface. But this is 

 exactly what is wanted ; for in order to stop a flying 



