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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[Junk, 



progress was a voluntary accomplishment, independent of its support, 

 and not the veritable means of that support itself, determined by the 

 conditions of the case alone. These conditions we have shown to be 

 the might and superficial dimensions of the suspending plane : and 

 bv these conditions, in the present case, observing an inclination of 3°, 

 we are referred to a velocity of 240, or more properly 280 miles an 

 hour. A modification of these conditions, involving an enlargement 

 of the surface or a diminution of the weight, is therefore, and abso- 

 lutely, the only existing means by which any part of this velocity 

 could be effectually dispensed with; a modification which, moreover, 

 we showed to be equally necessary to its success in another point of 

 view ; the accomplishment, namely, of its descent, consistently with 

 the preservation of human life, or even of the integrity of the ma- 

 chine itself. It only remains, on this head of inquiry, therefore, to 

 make a few remarks respecting the particular/oral which Mr. Henson 

 has adopted for this important portion of his aerial apparatus. 



Where so much more is required to be done than can be easily ac- 

 complished, and the utmost that we can reasonably hope to arrive at 

 is a very limited reduction of the essential difficulties of the case, a 

 lack of proper economy in the disposition of our resources becomes 

 a grevious error, and inevitably leads to the conclusion that chance or 

 mistaken analogy rather than the legitimate inductions of science 

 have had a share in determining the choice. To those who have not 

 considered the matter or made it the subject of actual experiment, it 

 may not readily suggest itself that the really effective obstacle to the 

 accomplishment of an aerial navigation, upon the principle of the 

 plan before us, consists in the difficulty of constructing a rigidly ex- 

 tended surface, of sufficient dimensions and sufficiently light to answer 

 the purpose required of it. Apart from this there is literally nothing 

 that interferes, nothing that has to be overcome: for in the attainment 

 of this object are merged all the obligations in respect of 

 which the want of it alone imposes, aud which constitutes in its de- 

 fault the existing obstacle to success. The difficulty which is here 

 alluded to, and which, be it observed, is interposed by nature herself, 

 in the essential properties of matter, depends upon the ratio in which 

 weight, or rather, its effects in pressure, increase in respect of the 

 distance at which it is suspended from its fulcrum or point of support, 

 and the impossibility of counteracting these effects by the interven- 

 tion of any means which do not also add to the forces, by the ope- 

 ration of which their adoption in the first instance was required. 

 The conditions of weight, and consequently the obligations of support, 

 increase, as we all know, in the ratio of the leverage, or horizontal 

 projection ; and this with such effect, as very soon to confound the 

 best directed efforts of the most ingenious architect to combine 

 solidi'y and lightness with extension in a plane of any magnitude that 

 is devoid of extrinsic sources of support. With these inherent and 

 inevitable peculiarities, it scarcely needs to be observed, the main 

 ob;< ct to be aimed at by those who have occasion to construct a sur- 

 face in which the qualities in question are required to be carried to 

 their extremest degree, is to have a form for that surface the most 

 compact, in which the largest area is contained within the least re- 

 mote limits ; an advantage which the circular alone of all others is 

 pre-eminently calculated to afford. In Mr. Hensou's scheme, however, 

 this has been entirely lost sight of, and, for what purpose it would be 

 hard to conjecture, a form has been adopted, in which the smallest 

 extent of surface is obtained in conjunction with the fullest develop- 

 ment of all the natural difficulties by which the case is peculiarly 

 beset. The stringency of this observation will be the more readily 

 perceived when we consider that the utmost amount of surface which 

 Mr. Henson has been able to accomplish, (for we will not suppose he 

 has stopped short of his ability in this most essential ingredient of 

 success,) involves an extension of 75 feet on either side the centre of 

 support, within which limits, had he adopted the circular form, he 

 might with equal facility have comprised an area of exactly four 

 times the extent ; the very quantity we have already shown to be the 

 least with which it would be possible to enable it to come with safety 

 to the ground. 



Besides this, there is another objection to the shape of Mr. Hen- 



son's plane, which deserves to be noticed ; namely, the superfluous 

 amount of horizontal resistance to which it is calculated to give rise. 

 The force of resistance, it is well known, depends upon the direction 

 of its development— is greatest when it is perpendicular, and dimi- 

 nishes with the obliquity of the impact. Now the whole of the re- 

 sistance experienced by the opposing front of Mr. Hensou's plane, is 

 of the former description, and consequently the greatest it could by 

 any possibility be made to encounter. Without pretending to form 

 any estimate of the actual amount of this force, we shall merely ob- 

 serve that by the adoption of a circular or even an elliptical form, 

 the greater part of it would have been effectively avoided. 



Nor must the question of danger be altogether overlooked in criti- 

 cising the properties of Mr. Hensou's plane. Depending entirely for 

 its stability upon the due strength and tension of the cords by which 

 it is supported, it is easy to see how precarious must be that form of 

 structure which at once involves the fewest number aud the greatest 

 length ; where the whole weight, situated in the centre, is sustained 

 by levers in one direction only, aud where, consequently, the rupture 

 of a single line of braces must be attended with the collapsion of the 

 whole mass and its unrestrained precipitation to the earth. 



To complete this survey, we will only add one more objection, 

 which, though we have placed it last, is by no means the least charac- 

 teristeric of those to the charge of which Mr. Henson's plane, in its 

 present form, is liable ; we mean the obstacle to its rectilinear motion, 

 arising out of the exaggerated inequality of the forces which it is 

 calculated to develop in its progress. If the opposite sides of the 

 suspending plane be in any way productive of different amounts of 

 resistance in passing through the air, (and no precision attainable by 

 art can prevent this conclusion iu some degree,) this difference acting 

 continuously and through the intervention of a lever of 75 feet in. 

 length, will create a re-action destructive of the regularity of its pro- 

 gress, which it will require the application of considerable powers to 

 be able effectually to counteract. Supposing, for instance, (what may 

 inevitably be apprehended,) that a dislocation or distension of any of 

 the numerous bracings by which the rigidity of the plane is to be se- 

 cured, should occur on either side of the machine more than on the 

 other, an alteration in the obliquity of the presentation of the sides 

 must ensue, and a disturbance of the equilibrium of resistance, which 

 if it be only equivalent to ten pounds (and at the rate of 210 miles 

 an hour, the perpendicular resistance upon a single square foot of 

 surface, would be equal to 288 pounds) at the distance of 75 feet from 

 the centre of motion, would influence its course with a diversion 

 equivalent to a pressure of 750 pounds, and acting continuously, oc- 

 casion a constant tendency to move iu the circumference of a circle, 

 only to be resisted by a rudder of suitable dimensions ; to the mani- 

 fest retardation of its speed, and the consequent expenditure of a 

 considerable amount of power. 



Why Mr. Henson should have fixed upon this form for the con- 

 struction of his suspending plane, we cannot pretend to surmise. All 

 we. can say is that, if it has been designed with a view to preserve 

 any analogy with the bird whose wings appear to be similarly ex- 

 tended in flight, the design is founded in a mistake. The bird re- 

 quires its wings to be laterally extended, that they may operate to 

 the greatest advantage in effectuating its propulsion through the air. 

 This purpose, however, in Mr. Henson's plan, is intended to be an- 

 swered by another expedient; namely, the revolving vanes. Tore- 

 tain the form after the purpose has been superseded, is to defeat not 

 to sustain the analogy designed. 



We have not stopped to examine the various modifications which 

 have been proposed in different quarters by way of improvement 

 upon this part of Mr. Hensou's machine. Two only of these mo- 

 difications we would particularize, because they have emanated 

 from, or obtained the sanction of, one justly celebrated for his scien- 

 tific attainments, and especially in matters relating to the present 

 subject: the first consists in doubling the amount of surface, by 

 placing tico planes, one over the other; and the second, in the adop- 

 tion of a conical or curved surface, as it were sunk a little in the 

 I middle, instead of one perfectly plane, with a view to escape the os- 



