128 Professor H. S. Hele-Shmv [March ;51^ 



problem which is very much simpler for land and water. The 

 human body itself, while of about equal specific gravity with water, is 

 about 800 times as heavy as air, and probably, taken in conjunction 

 with the motor and aeroplane, the weight which has to be supported 

 is several thousand times as heavy relatively to the air which it dis- 

 places. Inasmuch as the support of the air necessitates the use of an 

 inclined plane and a corresponding expenditure of energy, the speeds 

 made horizontally and independently uf the wind have, at the present 

 time, barely exceeded half the record speeds made on wheel vehicles. 

 As a matter of fact, only the other day the record for passenger flight 

 was broken by M. Nieuport at Mourmelon, when he flew with two 

 passengers for Ih. 4m. 58 l-5s., and covered 68*35 miles at an 

 average speed of 63 miles per hour. It is difficult to say exactly 

 what the true record speed at present is round a course, but we may 

 safely take it as probably under 70 miles an hour, the record being, so 

 far as I have been able to ascertain, by M. Nieuport on March 9 this 

 year at Chalons — 68 miles 168 yards in the hour. 



We now see the relative position of the record speeds in the three 

 elements on our speed chart. Fig. '6, and it is obvious that while on 

 land the speed has been far exceeded of the fastest animal, on water 

 it has probably only recently surpassed that speed, while in the air, in 

 all probability, it is still considerably below it. We must not, how- 

 ever, from this argue that flying speeds will for safe flying machines 

 rise so far beyond that of birds as land locomotion has risen above 

 the speed of animals, for it looks as if the speed records on land 

 would be at least equal for some time, if not greater, than that 

 possible with safety in the air. At the same time, there is no doubt 

 that speed is the one great factor of safety in flying, and aerial speed 

 records are sure to go on rising year by year, l)ut time does not 

 permit me to pursue this subject further to-night. 



Instead of vague surmises as to what may be done in the future, 

 let us spend a few minutes looking into the question of these limits. 



The two chief things on which the limit of speed in locomotion 

 will depend are : — 



(1) The motive power available. 



(2) The resistance, and the manner in which those resistances 

 operate. 



But inasmuch as we are not merely considering the human body 

 as a projectile, we do not take into account such speeds as have been 

 attained by man in such ways as, for instance, in a high dive, say, of 

 nearly 100 miles an hour, or even the thrilling descents such as are 

 made in a bobsleigh. We must really consider speeds which can be 

 made with safety ; and there are two further questions which arise : — 



(1) Knowledge as to possible obstacles, coupled with a power of 

 safely stopping within the distance to which our knowledge extends, 

 i.e. signalling and brakes. 



(2) Vibration. 



