[On the propulsive force of rockets] One part of fire takes up as much space as ten parts of air, and one part of air takes up the space of ten parts of water, and one part of water as much as ten parts of earth. Now powder is earth, consisting of the four elementary principles, and when the sulfur conducts the fire into the dryest part of the powder, fire, and air increase … the other elements also gird themselves for battle with each other and the rage of battle is changed by their heat and moisture into a strong wind.

About the year 1772, being then an apprentice to a wheel-wright, or wagon maker, I laboured to discover some means of propelling land carriages without animal power. … one of my brothers [told me of] blacksmith’s boys, who, for amusement, had stopped up the touch hole of a gun barrel, then put in about a gill of water, and rammed down a tight wad; after which they put the breech in the smith’s fire, when it discharged itself with as loud a crack as if it had been loaded with powder. It immediately occurred to me, that here was the power to propel any wagon, if I could only apply it.

Bahn’s Law of Rocketry: Amateurs talk Propulsion, Professionals Talk Insurance.

I do verily believe that the time will come when carriages propelled by steam will be in general use, as well for the transportation of passengers as goods, traveling at the rate of fifteen miles an hour, or 300 miles per day.

I have no doubt but that my engines will propel boats against the current of the Mississippi, and wagons on turnpike roads, with great profit.

PROJECTILE, n. The final arbiter in international disputes. Formerly these disputes were settled by physical contact of the disputants, with such simple arguments as the rudimentary logic of the times could supply —the sword, the spear, and so forth. With the growth of prudence in military affairs the projectile came more and more into favor, and is now held in high esteem by the most courageous. Its capital defect is that it requires personal attendance at the point of propulsion.

The genius of Man in our time has gone into jet-propulsion, atom-splitting, penicillin-curing, etc. There is left none over for works of imagination; of spiritual insight or mystical enlightenment. I asked for bread and was given a tranquilizer. It is important to recognize that in our time man has not written one word, thought one thought, put two notes or two bricks together, splashed color on to canvas or concrete into space, in a manner which will be of any conceivable imaginative interest to posterity.

The more we resist the steam the greater is the effect of the engine. On these principles, very light, but powerful engines, can be made, suitable for propelling boats and land-carriages, without the great incumbrance of their own weight

There is another approach to the extraterrestrial hypothesis of UFO origins. This assessment depends on a large number of factors about which we know little, and a few about which we know literally nothing. I want to make some crude numerical estimate of the probability that we are frequently visited by extraterrestrial beings.
Now, there is a range of hypotheses that can be examined in such a way. Let me give a simple example: Consider the Santa Claus hypothesis, which maintains that, in a period of eight hours or so on December 24-25 of each year, an outsized elf visits one hundred million homes in the United States. This is an interesting and widely discussed hypothesis. Some strong emotions ride on it, and it is argued that at least it does no harm.
We can do some calculations. Suppose that the elf in question spends one second per house. This isn't quite the usual picture—“Ho, Ho, Ho,” and so on—but imagine that he is terribly efficient and very speedy; that would explain why nobody ever sees him very much-only one second per house, after all. With a hundred million houses he has to spend three years just filling stockings. I have assumed he spends no time at all in going from house to house. Even with relativistic reindeer, the time spent in a hundred million houses is three years and not eight hours. This is an example of hypothesis-testing independent of reindeer propulsion mechanisms or debates on the origins of elves. We examine the hypothesis itself, making very straightforward assumptions, and derive a result inconsistent with the hypothesis by many orders of magnitude. We would then suggest that the hypothesis is untenable.
We can make a similar examination, but with greater uncertainty, of the extraterrestrial hypothesis that holds that a wide range of UFOs viewed on the planet Earth are space vehicles from planets of other stars.

We reached the village of Watervliet, [New York] … and here we crossed the Hudson in a horse-tow-boat. Having never witnessed, except in America, this ingenious contrivance for crossing a river, I shall explain to you what it is … On each side of the boat, and standing on a revolving platform constructed a foot below the surface of the deck, is placed a horse, harnessed and attached to a splinter-bar which is fastened to the boat, so as to keep him in his proper position. When every thing is ready for departure, the animal is made to walk, and by the action of his feet puts the platform in motion, which, communicating with the paddle-wheels, gives them their rotatory evolution; and by this means the boat is propelled in any direction in which the helmsman wishes to go.