limited field of view, greater apparent target speed, parallax errors, and the danger of keeping the eye against an eye stop. In the 1901 the Scientific Transactions of the Royal Dublin Society he described his invention as:

It was noted soon after its invention that the sight could be a good alternative to iron sights and also had uses in surveying and measuring equipment. The reflector sight was first used on German fighter aircraft in 1918 and widely adopted on all kinds of fighter and bomber aircraft in the 1930s. By World War II