78 



SCIENCE 



[Vol. XV II I. No. 444 



up to a certain limit which the experiments have not yet deter- 

 mined. This assertion, which I make here with the brevity neces- 

 sary in this resume, calls for a more ample demonstration, and re- 

 ceives 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 twenty metres in diameter, put in movement by a ten horse- 

 power steam-engine. They are chiefly as follows. 



(1) To compare the movements of planes or systems of planes, 

 the weights, surface, form, and variable arrangements, the whole 

 being always in a horizontal position, but disposed in such a man- 

 ner 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 horizontal 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 experiments which 

 have been carried out, let us take a horizontal plane, loaded (by 

 its own weight) with 464 grams, having a length 0.914 of a metre, 

 a width 0.102 of a metre, a thickness two millimetres, and a den- 

 sity about 1,900 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 1.23 metres, the time of fall in a vacuum being 

 0. .50 of a second. 



Horizontal velocities . . m. , 



Time taken to faU 

 from a constant 

 height of 1.33 me- 

 tres 0.53 s., 



10 m. 



15 m., 20 m. 



0.61s., 0.75 s., 1.05 s., 3.00 s. 



When the experiment is made under the best conditions it is 

 striking, because, the plane having no inclination, there is no ver- 

 tical component of apparent pressure to prolong the time of fall; 

 and yet, although the specific gravity is in this more than 1,900 

 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 observations of the same kind have 

 been made in numerous experiments with other planes, and un- 

 der more varied conditions. 



From that which precedes, the general conclusion may be de- 

 duced that the time of fall of a given body in air, whatever may 

 be its weight, may be indefinitely prolonged 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 con- 

 sequence of that which follows; we have established the necessity 

 of examining more attentively the practical possibility of an 

 art very admissible in theory — that of causing heavy and con- 

 veniently disposed bodies to slide or, if I may say so, to travel in 

 au-. 



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 5,380 grams per square metre, incUned at 

 dififerent angles, and moving in the dii-ection 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 support, the 

 velocity is regulated in such a manner that it will always be sub- 

 jected to a horizontal motion. 



The first column of the following table gives the angle (a) 

 with the horizon ; the second the corresponding velocity (V) of 

 planement — that is, the velocity which is exactly sufficient to 



sustain the plane in horizontal movement, 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 corre- 

 sponding velocities — a resistance that is shown by a dynamome- 

 ter. These three columns only contain the data of the same ex- 

 periment. 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 one horse-power engine ought to 

 cause to advance horizontally with the velocity V and at the angle 

 of inclination a. 



45 11.3 500 



30 10.6 375 



15 11.2 128 



10 12.4 88 



5 15.2 45 



2 20.0 20 



As to the values given in the last column, it is necessary to add 

 that my experiments demonstrate that, in rapid flight, one may 

 suppose such planes to have very small interstices, without dimin- 

 ishing 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 approxi- 

 mately 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 mo- 

 tors weighing less than five kilograms per horse-power have re- 

 cently been constructed. 



Although I have made use of planes for my quantitative experi- 

 ments, 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 descending with safety, be- 

 longs more to the art of which I have spoken than to my subject. 



The points that I have endeavored to demonstrate in the memoir 

 in question are — 



(1) That the force requisite to sustain inclined planes in hori 

 zontal aerial locomotion diminishes, instead of increasing, when 

 the velocity is augmented, and that up to very high velocities, — 

 a proposition the complete experimental demonstration of which 

 will be given in my memoir; but I hope that its apparent improb- 

 ability will be diminished by the examination of the preceding 

 examples. 



(2) That the work necessary to sustain in high velocity the 

 weights of an apparatus composed of planes and a motor may be 

 produced by motors so light as those that have actually been con- 

 structed, provided that care is taken to conveniently direct the 

 apparatus in free flight, with other conclusions of an analogous 

 character. 



I hope soon to have the honor of submitting a more complete 

 account of the experiments to the academy. 



OLD STANDARDS. 



By a curious accident it has just been discovered that the stan- 

 dard yard and certain other measures and weights which were 

 supposed to have been lost when the Houses of Parliament were 

 destroyed by fire in 1834 are still in existence. The following ac- 

 count of the matter, condensed from a statement in the London 

 Times, is given in a recent issue of Nature. 



A reference to the contemporary records shows that after the 

 fire the standard bars of 1758 and 1760 were both found among 

 the ruins, " but they were too much injured to indicate the meas- 

 ure of a yard which had been marked upon them." The principal 



