United States. Surgeon-General's Office, American Roentgen Ray Society · New York : Middleditch · leaf 207
e of the cornea, the entire instrument ispushed forward on its base until the ball presses intothe patients closed eye-lid approximately its thickness;the trigger spring is then released and the indicator-balland cone recede exactly 10 millimeters, thereby permit-ting the patient to open his eyes… … <*5 lit w Fig. 3. Position for first exposure.
