LIMITS TO HUMAN FLIGHT — WIMPERIS 581 



up till a mere 5 or 10 million years ago, the birds settled down to stability about 

 half-way through the Teritiary Epoch, about 20 or 30 millions of years back, 

 and since then, though they have doubtless sprouted out innumerable tiny side- 

 twigs of new species and genera, do not seem to have made any real evolutionary 

 progress. 



Nor, he adds, are they in the least likely to achieve any in the future 

 since they appear to have reached the limit of perfection attainable 

 in the circumstances prevailing upon the earth, by the kind of creature 

 which they are. Mankind has certainly speeded up the previous 

 rate of aeronautical evolution. 



HIGH SPEED 



I think I cannot do better than approach the problem of the attain- 

 ment of high speed than by quoting from the Creevey papers. The 

 adventure related, took place just over 100 years ago. 



To-day we had a lark of a very high order. Lady Wilton sent over yesterday 

 from Knowsley to say that the locomotive machine was to be upon the railway 

 at such a place at 12 o'clock for the Knowsley party to ride in if they liked, and 

 inviting this house to be of the party. So of course we were at our post in three 

 carriages and some horsemen at the hour appointed. I had the satisfaction, for 

 I can't call it pleasure, of taking a trip of 5 miles in it, which we did in just a 

 quarter of an hour. * * * The machine was occasionally made to put itself 

 out or go it; and then we went at the rate of 23 miles an hour. * * * But 

 the quickest motion is to me frightful: it is really flying, and it is impossible to 

 divest yourself of the notion of instant death to all upon the least accident happen- 

 ing * * * Altogether I am extremely glad indeed to have seen this miracle, 

 and to have travelled in it. Had I thought worse of it than I do, I should have 

 had the curiosity to try it; but having done so, I am quite satisfied with my first 

 achievement being my last. 



Perhaps it was his last but others were more adventurous. Around 

 the attainment of high speed, immense human interest has always 

 centered. The breaking of such records now rank as international 

 events, and the world probably spent a million pounds over the last 

 Schneider Trophy race. It is estimated that the "record" has been 

 rising steadily for 25 years at an average rate of 15 miles per hour 

 annually. Where is this to stop? Must it stop? 



The attainment of very high speed depends upon combining great 

 engine power with low airplane drag. It is less obvious how it will 

 depend upon the altitude of flight. The latter question, however, is 

 very important, and perhaps we may consider it first. As we increase 

 height we decrease air density, and therefore decrease drag, so that 

 flying at altitude, if speed is desired, seems good sense; but this 

 simple conclusion is complicated by the engine factor and several 

 others. Let me deal first with the engine. The engine power is as 

 much affected by change of air density as is the drag, and how do 

 these conflicting tendencies balance the one against the other? This 



