[SkyRat]

When a distinguished but elderly scientist says that something is possible, he is almost certainly right. When he says it is impossible, he is very probably wrong
-Arthur C. Clarke

Well informed people know it is impossible to transmit the voice over wires and that were it possible to do so, the thing would be of no practical value.
- Editorial in the Boston Post (1865)

Heavier-than-air flying machines are impossible.
- Lord Kelvin, ca. 1895, British mathematician and physicist

Radio has no future
- Lord Kelvin, ca. 1897

[Physicist]

Heavier-than-air flying machines are impossible. - Lord Kelvin, ca. 1895, British mathematician and physicist

I'd like to see a source for this. Certainly Kelvin knew that birds and insects were heavier than air.