1843.J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



2-2.i 



4. But if friction be a force which does not regard the condition of 

 motion, such is not the case with the resistance of the medium, which 

 yet remains to be noticed. Unfortunately, however, for Mr. Henson's 

 hypothesis, this force really pursues a directly opposite progression, 

 being absolutely none or of no effect in the first induction of motion, 

 and increasing in intensity and requirement of power in proportion as 

 it is more fully developed. It needs no laboured comment, therefore, 

 to point out how little colour the consideration of this force is calcu- 

 lated to give to the principle which Mr. Henson's contrivance is in- 

 tended to set up. And this completes the list of all those elements of 

 opposition which are called into play in the process of investing a 

 bodv with a given rate of motion. There are, it is true, other forces, 

 or as they may be more properly termed, accidental conditions, by 

 which a bodv may be detained at rest against the exercise of a greater 

 power than would be competent to continue it in motion after they 

 had been overcome. If a cart heavily laden, for instance, be left 

 standing for some time upon an imperfectly hard foundation, the 

 vheels will create for themselves a rut out of which they will require 

 to be extracted with a degree of force, the necessity for which is then 

 immediately dispensed with; or if it has to be dragged over such a 

 kind of road, the retardation of its course affected by the depression 

 of its wheels, which is greater the slower the rate, indicates the ne- 

 cessity for an accession of force to bring it up to a rate of motion in 

 which this condition is overcome, when it may, without prejudice, be 

 discontinued. Again, an object may be so circumstanced as not to be 

 able to exercise its means of propulsion to equal advantage in the 

 beginning as in the subsequent stages of its progress, and may there- 

 fore require the employment of a greater degree of power to acquire 

 than to maintain its destined condition of velocity; as exemplified in 

 the case of the larger birds labouring to ascend from the ground, 

 where the height of their bodies not permitting the full action of their 

 wings, they are obliged to make up the deficiency by the more forcible 

 and frequent repetition of the stroke, producing that appearance of 

 disproportionate exertion which has contributed to maintain, if not to 

 suggest, the delusion implied in Mr. Henson's expedient to supply the 

 inherent deficiency of his moving power. These, however, are all 

 obstructions of a kind which do not enter into the constitution of the 

 forces with which the aerial machine upon Mr. Henson's principle has 

 to contend. These forces, with which alone we have any concern, are 

 simply those enumerated above, of which we have seen there is not 

 one that offers any more opposition to the induction or establishment 

 of a given rate of motion than it does to its continuance, and conse- 

 quently imposes no obligation in respect of power to begin with, that 

 it does not equally exact during the remainder of its career. 



Had we had to deal with the contrivance proposed by Mr. Henson 

 alone, we should not have had occasion for all this elaborate investi- 

 gation in order to prove its insufficiency for the purpose ascribed to 

 it. The force acquired by a descent, however accomplished or 

 applied, must be assuredly inadequate to the production of any effects 

 that could extend to a condition of elevation superior to that from 

 which it had originated ; as might be concluded at once from a con- 

 sideration of the properties of the pendulum, which, in so far as re- 

 gards the infkience of gravity in communicating motion, is a parallel 

 case with that which we are supposing before us. But here the 

 parallelism ends ; nor can any inference be drawn, as so confidently 

 contended for (see Mechanic's Magazine, &c.) Irom the continuance 

 of the motion in the one case to its continuance in the other by the 

 instrumentality of a power inferior to what is required for its original 

 establishment. The pendulum is not, in fact, kept in motion by a 

 power at all less than that by which it has been started, as a little 

 consideration will evince. The force which puts the pendulum in 

 motion is that employed in raising it to a certain height, from which 

 it is allowed to descend by its own gravity. In this descent it acquires 

 a force which would be equal to the original, and by which it would 

 be carried up to an equal height on the other side, and thus recipro- 

 cate the movement without extrinsic assistance, were it not for the 

 resistance of the air it encounters, and the friction of the parts in 

 contact by which a part of it becornps expended or consumed. This 



portion is supplied by means of a spring. But it is not the spring 

 that maintains the movement of the pendulum, but the attraction of 

 gravitation conjointly with it, which together are exactly equal to the 

 original impulse. Here, however, is nothing analogous to the case 

 of Mr. Henson's machine, acquiring a momentum by means of a single 

 descent down a plane, not to be repeated, and unprovided with a 

 power equal to the counteracting forces, the friction and resistance of 

 the air, with which it has to contend. 



Having now conducted our readers through the mazes of this intri- 

 cate, but we trust not uninteresting nor profitless inquiry, we would 

 conclude with a few observations touching the prospects of that 

 " consummation so devoutly to be wished for," — the establishment of 

 a successful mode of navigating the skies. One thing is clear; that, 

 upon the principle of the plan we have been investigating, it is to- 

 tally out of the question. The obligations imposed by the necessities 

 of support, are of so exaggerated a character, that by no modification 

 of construction, or application of new resources, can it ever rationally 

 be expected to fulfil them. In an early part of this analysis we had 

 occasion to point out the conditions in subservience to which these 

 obligations are imposed. We there showed that the circumstance 

 upon which the difficulties of the case really depended, was the rela- 

 tion of the weight of the machine to the superficial magnitude of the 

 suspending plane, whereby alone the rate of progression was ascer- 

 tained, to which all the requirements of power are ultimately refer- 

 able. By a reduction of the one or an enlargement of the other, 

 therefore, is this principle solely improveable to the attainment, of 

 of success ; and that, to an extent which a retrospect of past expe- 

 riments and a general consideration of the nature of the case alike 

 evince to be far beyond the reach of art to accomplish. Referring to 

 the process by which the calculations in the preceding table may be 

 applied to determine the conditions of flight assignable to other ma- 

 chines of the like principle, as detailed in the note annexed, it will be 

 seen that the smallest sized surface which could be made effectual to 

 support the weight of Mr. Henson's machine, with the exercise of Mr. 

 Henson's power, taking it at the greatest, would require to be upwards 

 of 100,000 square feet in extent ; or somewhat more than 22 times 

 the area which Mr. Henson has provided for the purpose. Nor can any 

 argument in contravention of this conclusion be drawn from the pro- 

 portion between the weight and superficial magnitude of the wings of 

 birds, upon which so much reliance is wont to be placed by those who 

 have hitherto written upon the subject. There is, in truth, no analogy 

 whatever between the cases ; neither consequently can any inference 

 be legitimately drawn from what is effected in the one to what is 

 possible to be effected in the other. The weight of birds in propor- 

 tion to the size of their wings, may or may not be as great or greater 

 than that attainable by art as between the weight of the aerial ma- 

 chine and the superficial contents of the suspending plane. Their 

 purposes are entirely distinct, and accomplished through the interven- 

 tion of essentially distinct properties. The bird possesses a power 

 of unlimitedly increasing the reaction of its wings by their voluntary 

 impact, which the rigidly suspended plane is devoid of, and which, by 

 affording a compensation for any deficiency of size, neutralises all ar- 

 guments founded upon a consideration of the relative proportion of 

 weight, and removes the case out of all analogy with the machine 

 constructed upon the principle of the plan before us. 



Disappointed, therefore, in our expectations of success in this 

 quarter, it may be asked, whither are we to direct our attention in 

 order to discover the means of solving this perplexing but still inte- 

 resting problem? The answer will most naturally suggest itself from 

 a consideration of the circumstances to which the failure of all the 

 attempts to navigate the atmosphere by mere mechanical impulse, the 

 present among the rest, is entirely to be ascribed. These circum- 

 stances we have already specified in the exaggerated nature and 

 amount of the obligations of support, occasioned entirely by the 

 tenuity of medium and the force of gravitation; in the teeth of 

 which we feel no hesitation in declaring our opinion, no process 

 founded upon simple mechanical reaction ever can succeed; for even 



