Francis Galton would have been the famous eccentric scientist in any family except the one he was born into. The Darwin, Wedgewood, and Galton families were thick with scientists, and Francis wasn't anywhere near the favorite. He did leave his mark in both large and small ways. The dog whistle is one of the smaller ways.
Francis Galton and Charles Darwin were contemporaries, and were close. Charles' grandfather was the sibling of Francis' grandmother, making Francis Galton, technically, a half-cousin to Charles Darwin. The entire family was scientifically-inclined, and they were always in and out of each-other's theories. Galton was more mathematically-inclined than Darwin, and used his math knowledge to come up with the idea of "regression to the mean."
Regression to the mean is why we believe that certain awards are cursed. Someone who wins an Oscar will act in crap thereafter. Someone who wins MVP will see their performance go downhill. When someone wins a "best newcomer" award in the music business, they're never heard from again. This isn't because the awards are wrong, or "cursed," but because they, by definition, are awarded for exceptional performance. Even gifted people tend towards average performance. Galton showed that regression to the mean was also a factor of biology. Two exceptionally tall people may produce even taller offspring, but overall, their children and grandchildren will regress to the mean – becoming average height. Galton became obsessed with an idea of fighting regression to the mean, especially in terms of intelligence. Unfortunately, when he applied this to Darwin's theories, he came up with the idea of eugenics. Galton wanted to create a world full of geniuses. Although he died in 1911, well before the idea of eugenics reached its most horrific point, his writings on the subject still remain controversial.
Galton also invented something more useful – the dog whistle. He wanted to perform experiments using wavelengths of sound too high for a human to hear. How could he be sure that something was making a sound if he couldn't hear it? It seems that, at first, he settled on using a principle that he knew would work, and extending it. He created something like a slide whistle – a brass tube with a sliding piece that could make the note produced by blowing in the tube higher and higher. Once the adjustable piece slid past a certain point, Galton couldn't hear it, but knew the whistle was still producing sound.
After that, he got a bit silly, and took his whistle to the London zoo, testing it out on various animals. According to his notes, "It certainly annoyed some of the lions." Later he would walk down the street, noting which dogs responded most to his supersonic whistle. He found that small dogs could hear higher pitches than large dogs. Cats, Galton noted, heard high-pitched tones best of all. They just refused to respond to the whistle in any useful way, which is why it is not called "the cat whistle."