Or about 29 tons, which may be divided in any convenient proportions between the engine-power and its apparatus for waftage, the crew, and the cargo.

Before this can be done, it is necessary to have an estimate of the resistance of such a balloon when driven through the air at the velocity we propose to obtain. Extensive as this balloon seems to be, according to the best data, it could not be driven by the engines, &e. it could carry, at more than 17 miles per hour; and is better qualified to be driven at 14. It is extremely probable, however, that our data give the resistances of curved vessels considerably greater than is found to be the case in practice; but let us rigidly adhere to that which our present degree of information points out, and consider 14 miles per hour as the intended speed of our balloon. At this velocity there will be a resistance of 9 lbs. to the square yard when directly opposed to the current ;-hence, as the greatest cross-section of this balloon contains 710 square yards, the direct resistance of such a surface would be 6390 lbs. Mr. Robins found that a sphere only meets with about one-third of the resistance of its great circle, being as 1 to 27; others have found it still less, but experiments are scarce on this subject. With a view to the present inquiry, I made a light case of papers, glued together over a true spheroidal mould, 18 inches long by 6 in diameter, and loaded it so as to fall through the air in the line of its longer axis.

A circle of 6 inches diameter was then loaded till it fell with equal velocity, keeping perpendicular, to the line of its fall, the weight required to drag the flat circle with equal speed, side by side, through a fall of 30 feet, was 4.8 greater than that of the spheroid (of course the whole weight of each apparatus was thus the measure of the resistance.) The additional weights used to bring the circle to an equal velocity with the spheroid, were so arranged within similar cases, as to give equal resistance. This spheroid was just three times the length of its minor diameter; whereas the proposed balloon is 3 times longer than its breadth, which will materially diminish its resistance— and it may, therefore, be safely taken at not more than a sixth part of the resistance of its great circle, and in this case

*

*Mr. Tredgold, at p. 330 of his excellent work on the steam-engine, gives us all the particulars of

the resistance of the balloon at the pro

posed velocity will be

(6390)

or 1065lbs. -and as the speed at which this force must be supplied is 14 miles per hour, or 21 feet per second, it is equal to 1065 × 21, or 22365lbs. raised one foot high per second, which divided by 550, the number of pounds raised one foot high by a steam-horse, quotes the power required as that of rather less than 41 steamhorses, call it in round numbers #40-horse power, provided it could be applied from a solid fulcrum on the earth; but whatever kind of waftage may be employed, there will be a loss of power by its acting upon a rare and also a receding medium.

For the sake of perspicuity, suppose that the surface employed to propel the balloon be equal to that of its great circle, then it will receive as much resistance (following the law of the squares of the velocity, and the resistance of the spheroid being onesixth of that of the great circle) at about 8 feet velocity, as the balloon does at 21 feet; but before the wafting surface can give this resistance, it must go back with 8 feet more speed than the balloon goes forward, so that the engine-power is working at a velocity of (21 +8}) 29} feet per second, and this requires the power to be increased as 21, the former velocity, is to 29, or from a 40 to a 57 horse-power. Let us, then, consider our balloon as requiring, in round numbers, a 60-horse power.

The weight of the engine at 510lbs. per horse-power, with a load of fuel and water for four hours, will be 30,600lbs., which deducted from the 66,237, leaves 35,637lbs. of free floatage. Suppose the machinery for waftage to weigh as much as 13,000lbs., then there would still remain 22,637lbs. to convey passengers or cargo, say 100 men and their ordinary goods, or 10 men and a cargo of 21,000lbs. -about 9 tons.

This estimate was made on the plan of the direct waft backwards, merely for the sake of being more readily followed in its

the James Watt steam-boat, the length of which is to its greatest cross-section under water, as 5.7 to 1; and when the power which its engines can supply at the velocity, the paddles move with in still water is taken as a criterion of its only opposing force, the resistance, it does not appear to be more than one-sixteenth part of what the crosssection would receive. Hence we are probably allowing a much greater resistance to our balloon than on a large scale it will receive.

bers, say a 50-horse power in lieu of the 60-horse power on the former plan. This cannot be proved without a complicate diagram, and an explanation that would obtrude too much upon your pages, and most probably on the patience of your readers on the present occasion.

This will enable us either to add 5,000 more to the cargo, or, by using a 60-horse engine, to go with more speed.

Many persons erroneously suppose that any propelling force of waftage, when acting in the direction of the car, will not tend to propel the balloon above it. Let A, fig. 1, plate 3, be a balloon; let B be the position of its car, propelled beyond its centre of suspension, A, by any given power of waftage. Draw AC perpendicular, and CB parallel to the horizon; and let these lines be made in the same ratio to each other as the weight of the car is to the propelling power; then the line AB will represent the whole action of the car upon the balloon. Draw AD and BD respectively parallel to the two former lines; and as the floatage of the balloon is equal to the weight of the car, BD will as truly represent the floatage as AC does the weight; and, as the propelling power is, as soon as the speed becomes uniform, equal to the resistance, being the cause and measure of it, AD must as truly represent the resistance as its equal CB does that of the propelling power. In this position, then, all the powers are balanced in equilibrio;

but there will be no resistance till the balloon has the velocity necessary to generate it, and this it finds at the same speed in the line A D, as if it were moving along its equal C B.

I will here take advantage of the same diagram to observe, that if a balloon be supposed to be at anchor in a gale of wind, by the car being secured to the ground, and the line AD be taken to represent the force of the wind, and BD the power of floatage, then A B will be the position the cordage will fall back to. The resistance to the prow of the balloon in question, at a hurricane of 60 miles per hour, would be about 20,000lbs.-deducting the car then on the ground, its floatage would be about 63,000-so that it would fall back about one part in three, which are the proportions purposely taken in the diagram, in order to prove that permanently-filled balloons would ride out

storms when properly secured, without the danger of being driven to the earth and damaged.

Some persons are, however, disposed to strike at the root of all discussion as to steering balloons, by affirming that no waftage can propel bodies suspended in one and the same element in which the waftage takes place. These persons I will refer to p. 172 of Nicholson'e Chemical Journal for 1809, where they will find a description of a small machine, which they can make for themselves in a few minutes, that will elevate its own weight from the table to the ceiling, merely by the waftage it creates. The machine I have there described is a mere toy, but the principle on which it acts is capable of the most powerful and extensive application. I send you a view of its application to driving balloons, copied from a paper of mine at p. 81 of the Philosophical Magazine for 1817 (see plate 2, fig. 1), where there is likewise given a side elevation of a balloon with oblique wing waftage (fig. 2). The former by vanes revolving on an axis, the other by the heeling up and down of the surfaces in a reciprocating action, as in the bird's wing.

There is in one of the early volumes of the Philosophical Transactions, an account of propelling a boat with considerable velocity by men working this sort of waftage against the air; but I should prefer trying the more uniform action of the oblique vanes. More than one may be used on the same axis; and they may be so constructed as readily to apply their power, either to propel or retard, elevate or depress, as occasion may momentarily require. This will be obvious on inspecting fig. 2, plate 3.

Let the power of the engine communicate opposite movements to the reversed sets of fliers, C and D, through the cylindrical shaft A, and the wheels connecting them; the whole free power of the waftage will act in the line of their axis of motion. Conceive this axis to be moved into any position with respect to the horizon, by turning the hollow mast B (by which, through a suitable collar or socket the apparatus is supported from the car), and the balloon will be propelled accordingly. In the balloon we have been estimating, the four sets of such fliers would have to be 10 yards in mast or radius; and each sail would contain 30

square yards of surface. The figure given is intended merely to explain the principle of this action in the most distinct manner. In practice, this fabric, to unite strength with lightness, would be braced like the masts and sails of a boat; and its main strength derived from the ropes or metallic rods forming three braces.

Communicating centrifugal force to air by means of a hollow drum and fans worked by the steam-engine, is another means of getting a propelling power conveniently applicable in every direction that may be required; for by having a moveable mouth-piece, from which the air escapes, the re-action will always be in the opposite direction. Though convenient in this respect, it is too wasteful of power to be used for balloons, unless for small experimental purposes. Many other considerations remain untouched, upon; but I have already obtruded too much upon your pages with these dry details. The subject, however, is one of great interest, not merely in a mechanical point of view, but as to its stupendous effects on mankind at large; civilisation and, I trust, perpetual peace are in its train of consequences.

To such as have honoured me by wading through the train of this investigation, I will beg to remark, that they must not blame me for wilfully introducing such acres of cloth to their notice. Calculation from well-known data proves that balloons can only be driven with sufficient speed to be useful on the scale of magnitude I have pointed out. Let the question be put where it truly rests, whether such fabrics can or cannot be made and managed. The case is one evidently too great for individuals to make efficient experiments upon; and I am glad to see that some of your corre spondents have recommended a subscription purse, and I hope that plan may be followed up. I proposed this in the year 1817, in the following terms (page 28, vol. 1., Philosophical Magazine):—

"We, the undersigned parties, enter into the following subscription for the purpose of ascertaining how far the principle of balloons supporting heavy burthens in the air may be made useful as a means of conveyance.

"No person to be called upon for his subscription money till at least 10007. be subscribed for.

"When the subscription has reached this

amount, an annual Committee of seven of the subscribers to be elected. Every sub. scriber of 1., and of less than 51., to have one vote. Subscribers of 51. to have two votes; and subscribers of larger sums to have one additional vote for every additional 51. they subscribe.

"No experiments to be undertaken but by order of the Committee, who may call in the advice of such civil engineers as they chose to consult.

"An annual report of the application of the funds, and the result of the experiments made, to be printed for the use of the subscribers.

"These regulations being the basis on which the subscription is made, cannot be altered; but subsequent rules not militating against these, may be entered into at a gene ral meeting of the subscribers expressly con vened for the purpose."

The late Mr. Lovel Edgeworth immediately before his death became a sub scriber of 507. towards this fund, which his deservedly celebrated daughter sub sequently offered to make good. Mr. Evans also became a subscriber; but the age was not then ripe for the subject-steam-boats were in their in fancy, and railroad velocity unknown; twenty miles an hour then seemed monstrous and chimerical; now our only fear is that balloons will not have speed enough to satisfy our locomotive mania. I must not mention the respected name of Edgeworth without stating that he puts in a previous claim to that of Mr. Evans (see Philosophical Magazine, for 1816, p. 185,) to the principle of steer ing balloons on the tacking plan by the use of the inclined plain. He appears to have communicated the plan to Monsieur Mr. Montgolfier in the year 1782. Evans is, however, the first person that has proved the invention experimentally.

Balloons, as has been long ago observed, ought not to be made all in one, but have several departments for the gas, like "the stomach of a leech,"-aud should the promoters of aerial navigation get up a purse and combine their efforts during the present season, I should strongly recommend that Mr. Green's large balloon, and that gentleman's great experience and skill, be put in requisition; that two other of the largest balloons that are in town be packed at opposite sides of this large one, under one netting made in compartments for the purpose; the whole free floatage may then be ex