[3] Percival first ascended in a balloon at the age of eight with his father over the Crystal Palace.

[3] In a November 1909 letter to the editor of Flight magazine, he claimed to have made eight "Cross-Sea Balloon Voyages", often with passengers.

[4] His February 1898 crossing from England to France, accompanied by Pearson's Magazine journalist George Griffith, was reported in The New York Times.

[6] Ram Chandra Chatterjee took lessons from him and flew with him on 10 April,[7] becoming the first Indian aeronaut to fly solo later that same month.

Spencer died at his home in Aberdeen Park, Highbury on 11 April 1913, after contracting bronchial pneumonia.