278 



NATURE 



[July 23, 1891 



also of the theory underlying them, it appears to be demon- 

 strated that if, in an aerial movement, we have a plane 

 of determined dimensions and weight, inclined at such 

 angles and moving with such velocities that it is always 

 exactly sustained in horizontal flight, the more the 

 velocity is augmented the greater is the force necessary 

 to diminish the sustaining power. It follows that there 

 will be increasing economy of force for each augmentation 

 of velocity, up to a certain limit which the experiments 

 have not yet determined. This assertion, which I make 

 here with the brevity necessary in this risiivte, calls for a 

 more ample demonstration, and receives it in the memoir 

 that I have mentioned. 



The experiments which I have made during the last 

 four years have been executed with an apparatus having 

 revolving arms about 20 metres in diameter, put in 

 movement by a 10 horse-power steam-engine. They are 

 chiefly as follows : — 



(i) To compare the movements of planes or systems 

 of planes, the weights, surface, form, and variable arrange- 

 ments, the whole being always in a horizontal position, 

 but disposed in such a manner that it could fall freely. 



(2) To determine the work necessary to move such 

 planes or systems of planes, when they are inclined, and 

 possess velocities sufficient for them to be sustained by 

 the reaction of the air in all the conditions of free hori- 

 zontal flight. 



(3) To examine the motions of aerostats provided with 

 their own motors, and various other analogous questions 

 that I shall not mention here. 



As a specific example of the first category of experi- 

 ments which have been carried out, let us take a hori- 

 zontal plane, loaded (by its own weight) with 464 grams, 

 having a length 0-914 metre, a width 0-102 metre, a 

 thickness 2 mm., and a density about 1900 times greater 

 than that of the surrounding air, acted on in the direction 

 of its length by a horizontal force, but able to fall freely. 



The first line below gives the horizontal velocities in 

 metres per second ; the second the time that the body 

 took to fall in air from a constant height of r22 metres, 

 the time of fall in:a vacuum being 0-50 second. 



Horizontal velocities ... om., 5111., lom., 15m., 20m. 

 Time taken to fall from a \ 



constant height of 1-22 .^0-533., o-6is., 0-753., i"o5s., 2-oos. 



metres ) 



When the experiment is made under the best condi- 

 tions it is striking, because, the plane having no inclina- 

 tion, there is no vertical component of apparent pressure 

 to prolong the time of fall ; and yet, although the specific 

 gravity is in this more than 1900 times that of the air, 

 and although the body is quite free to fall, it descends 

 very slowly, as if its weight were diminished a great 

 number of times. What is more, the increase in the 

 time of fall is even greater than the acceleration of 

 the lateral movement. 



The same plane, under the same conditions, except 

 that it was moved in the direction of its length, gave 

 analogous but much more marked results ; and some ob- 

 servations of the same kind have been made in numerous 

 experiments with other planes, and under more varied 

 conditions. 



From that which precedes, the general conclusion may 

 be deduced that the time of fall of a given body in air, 

 whatever may be its weight, may be indefinitely pro- 

 longed by lateral motion, and this result indicates the 

 account that ought to be taken of the inertia of air, in 

 aerial locomotion, a property which, if it has not been 

 neglected in this case, has certainly not received up to 

 the present the attention that is due to it. By this (and 

 also in consequence of that which follows) we have 

 •established the necessity of examining more attentively 

 the practical possibility of an art very admissible in theory 



NO. 1134, VOL. 44] 



— that of causing heavy and conveniently disposed bodies 

 to slide or, if 1 may say so, to travel in air. 



In order to indicate by another specific example the 

 nature of the data obtained in the second category of my 

 experiments, I will cite the results found with the same 

 plane, but carrying a weight of 500 grams, that is 5380 

 grams per square metre, inclined at different angles, and 

 moving in the direction of its length. It is entirely free 

 to rise under the pressure of the air, as in the first 

 example it was free to fall ; but when it has left its sup- 

 port, the velocity is regulated in such a manner that it 

 will always be subjected to a horizontal motion. 



The first column of the following table gives the angle 

 (a) with the horizon ; the second the corresponding 

 velocity (V) oi plane7nent — that is, the velocity which is 

 exactly sufficient to sustain the plane in horizontal move- 

 ment, when the reaction of the air causes it to rise from 

 its support ; the third column indicates in grams the 

 resistances to the movement forward for the correspond- 

 ing velocities— a resistance that is shown by a dynamo- 

 meter. These three columns only contain the data of 

 the same experiment. The fourth column shows the 

 product of the values indicated in the second and third — 

 that is to say, the work T, in kilogram-metres per second, 

 which has overcome the resistance. Finally, the fifth 

 column, P, designates the weight in kilograms of a system 

 of such planes that a i horse- power engine ought to 

 cause to advance horizontally with the velocity V and at 

 the angle of inclination a. 



X 60 



6-8 

 130 



26-5 

 34-8 

 55-5 

 95-0 



As to the values given in the last column, it is neces- 

 sary to add that my experiments demonstrate that, in 

 rapid flight, one may suppose such planes to have very 

 small interstices, without diminishing sensibly the power 

 of support of any of them. 



It is also necessary to remark that the considerable 

 weights given here to the planes have only the object 

 of facilitating the quantitative experiments. I have 

 found that surfaces approximately plane, and weighing 

 ten times less, are sufficiently strong to be employed in 

 flight, such as has been actually obtained, so that in the 

 last case more than 85 kilograms are disposable for 

 motors and other accessories. As a matter of fact, 

 complete motors weighing less than five kilograms per 

 horse-power have recently been constructed. 



Although I have made use of planes for my quantitative 

 experiments, I do not regard this form of surface as that 

 which gives the best results. I think, therefore, that the 

 weights I have given in the last column may be considered 

 as less than those that could be transported with the 

 corresponding velocities, if in free flight one is able to 

 guide the movement in such a manner as to assure 

 horizontal locomotion— an essential condition to the 

 economical employment of the power at our disposal. 



The execution of these conditions, as of those that 

 impose the practical necessity of ascending and descend- 

 ing with safety, belongs more to the art of which I have 

 spoken than to my subject. 



The points that I have endeavoured to demonstrate in 

 the memoir in question are :~ 



(i) That the force requisite to sustain inclined planes in 

 horizontal aerial locomotion diminishes, instead of in- 

 creasing, when the velocity is augmented ; and that up 

 to very high velocities— a proposition the complete ex- 

 perimental demonstration of which will be given in my 

 memoir; but I hope that its apparent improbability 



