View source for Benjamin Franklin to John Ingenhousz 16-Jan-1784

Franklin discusses the [[Frères Montgolfier|Montgolfier]] demonstration and its implications. And, in more detail, the balloon of [[Jacques Charles]] and the [[Frères Roberts]]. The latter, he writes, required a large amount of inflammable air ([[hydrogen]]), which took 2–3 days to fill.

<blockquote>It had a ''soupape'', or valve, near the top which they could open by pulling a string and thereby let out some air when they had a mind to descend; and they discharged some of their ballast of sand when they would rise again. A great deal of air must have been let out when they landed so that the loose part might envelop one of them; yet, the car being lightened by that one getting out of it, there was enough left to carry up the other rapidly. They had no fire with them. That is used only in M. Montgolfier's globe which is open at the bottom and straw constantly burnt to keep it up. This kind is sooner and cheaper filled, but must be of much greater dimensions to carry up the same weight, since air rarefied by heat is only twice as light as common air, and inflammable air ten times lighter.</blockquote>

Franklin also describes the hazards to an inventor of advertising a public demonstration and then failing:

<blockquote>I is a serious thing to draw out from their affairs all the inhabitants of a great city and its environs, and a disappointment makes them angry. At Bordeaux lately a person pretended to send up a balloon, and had received money from many people, but not being able to make it rise, the populace were so exasperated that they pulled down his house, and had like to have killed him.</blockquote>

He speculates that aeronautics will make war impossible because of the difficulty of defending against [[military|aerial attack]].

=== Sources ===
* ''[[Aeronautical Annual]]'', vol. 1 (1895), citing ''The Works of Benjamin Franklin'' by Jared Sparks (Boston, 1838)

{{Letter
|Sender=Benjamin Franklin
|Recipient=Jan Ingenhousz
|Date sent=16-Jan-1784
|From location=Passy, France
|To location=
|Communication type=
|Language=English
|Refers to flight=1
|Tech field=balloon; LTA; military; hydrogen
|Length=
|Notes and sources=
}}