506 FLIGHT AND FLYING MACHINES. 
air, if not loaded too heavily in front, but if the back corners are curled 
up a little the glider begins to curve up at once, it tips down and up 
and the result is, that it ends by falling backwards or rolling over and 
over. I will try it from a slight height; of course it will not glide 
well, but you will see that the first thing it does is to curve up. We 
will now turn the corners over the other way and make them curve 
downwards. You will find that this glider turns downwards at once 
and soon turns topsy-turvy. I have here another paper glider more 
resembling a bird in shape which I hope to send across the room, but 
if if does not it will show you how difficult it is to balance these gliders, 
it will probably turn a little to one side, I will now try and curve it 
slightly in the other direction. You saw that I gave only the slightest 
bend to the paper on the side I wanted it to go, and yet the glider went 
perfectly straight instead of curving round. This shows what a very 
little will alter the motion of anything gliding through the air; in fact 
a friend of mine advised me on no account to throw off gliders in illus- 
tration of my lecture because they were certain to go wrong. 
What Herr Lilienthal has accomplished in Germany, Mr. Pilcher, of 
Glasgow, has recently achieved on the Clyde. His machines can be folded 
up for transport and are very portable; you see they fold up into quite 
a small space. ‘The first machine Mr. Pilcher constructed was made 
with very much upturned wings—the wings tipped up considerably, 
and there was only a vertical rudder, not a horizontal one. But it was 
found that the machine pitched somewhat in the same way as a paper 
glider will pitch ifits tail is turned too much upwards, so that the machine 
was rather dangerous to experiment on, because, of course, if a machine 
with a man on it were to turn over (like gliders have a habit of doing) 
it would be rather a serious matter. So Mr. Pilcher added a horizontal 
rudder as well which made it balance much better. He found, however, 
that although the \/ shape of the wings made the machine very steady 
when sailing against a head-wind,a side wind was apt to tip it over, so he 
had another machine made with the tips of the wings flat instead of being 
curved up, but the wings were now placed at nearly the height of his 
head. That, however, did not answer very well as it was very difficult 
to balance with the weight so far below the wing surface. Accordingly 
Mr. Pilcher took his first machine and bent the wings quite flat at the 
tips; and he found that by having the wings so much lower down he 
could balance much more easily. Of course, if the weight were to be too 
high up, the equilibrium would be unstable; and elementary considera- 
tions might suggest that the stability of the apparatus was greater the 
lower the centre of gravity. The results of Mr. Pilcher’s experiments 
show that this question of balancing cannot be treated as a mero 
statical problem, and that it is one of the most important factors in the 
problem of artificial flight. With the machine in the new modified 
form, Mr. Pilcher could sustain himself in the air for several seconds, 
and he was sometimes picked up by the wind and lifted as much as 20 
feet above the ground; and when there was not sufficient wind he got 
someone to pull him along by means of a string, like a kite, or to hold 
him against the wind. In some cases quite a moderate force was 
sufficient to hold the machine in mid air. The string could often even 
be pulled with one finger, 
