74 LAWRENCE HARGRAVE. 



visible under surface of the stationary machine is not the under 

 surface of the flying-macliine as it carries along with it and rests on 

 a cushion of air more or less wedge shaped : and that the angle of 

 this air cushion is self-adjusting for varying speeds within some 

 unascertained limits so long as the machine is balanced by having 

 from 20 to 25 per cent, of the area in advance of the centre of 

 gravity. 



Fig. 7 IS to shew what is supposed to be the state of tlie an- 

 on and in which the machine moves. AB represents the vertical 

 longitudinal section of the body plane. The circles and arrows 

 are sections of transverse horizontal vortices or air rollers 

 originated by the friction of the paper surface on the undisturbed 

 air ; tliese gradually work towards the tail and come to rest again 

 after the machine has passed. There may be one or many layers 

 of these anticyclonic vortices, but one is sufficient for this explan- 

 ation, and in the figure it is greatly exaggerated, tlie pressure is 

 supposed to be highest at the centres of the vortices, and their 

 diameters to increase as they pass aft. 



You will observe that the breasts of the inequalities or wa\es 

 adhering more or less closely to the paper and marked C, D, E, 

 F etc., are steepest when the vortices are small and close together, 



plane supports half the weight, and that the projections of tlie>»' 

 declivities represent an approximation to what' is in effect the 

 curved bottom of the flying machine LMB. 



Again, suppose the visible under surface to be more uneven, 

 and that the air rollers pass very slowly towards the stern, they 

 then become, as it were, part of the structure and the lower forward 

 parts of their circumferences Z,Y,X &:c. become the bearing surface 

 of the machine. The upper surface must be affected in a similar 

 way, though it is thought that the vortices would have low pressure 

 centres and large diameters producing a less curved invisible top 

 JKB to the machine. It will be readily seen tliat if the speed 

 increases the vortices have less time to increase in diameter and 

 thei-efore both top and bottom curves will be flatter. 



Pttli.ips some of the members have hauled a punt over a flat 

 sandy beach and have noticed that when there is a little water- on 

 the sand though not sufficient to float the punt, if the bow he 

 raised and tlien dropped suddenly on the water and pulled forward 

 before the water has time to squeeze out at the sides, a long 

 distance may be traver-sed with very little labour. And wliy ? 

 Because the punt is on water rollers. This theory may be contrary 



hope to be set right by those wlio can interpret the facts better. 



