A og whistle (also known as silent whistle or Galton's whistle) is a type of whistle used in the training of dogs and cats. It was invented by Francis Galton. This is discussed quite briefly in his book Inquiries into Human Faculty and its Development (Galton 1883:27). In his discussion (Galton 1883:26-27) of his experiments to test the range of frequencies that could be heard by various animals including humans, he notes that cats had the most sensitive hearing, being able to hear notes too shrill for humans to hear from a considerable distance, and small dogs can also hear these notes, while large dogs cannot. This book may not currently be in print, but is available in two formats, HTML and PDF (the PDF can be downloaded) at