To measure intra-ocular tension the tonometer is placed with its concave member a on the eyeball and sleeve 1 is gradually lowered. Lowered together with sleeve 1 are pin e and weight A of lever 2. The motion of weight A is transmitted through links 2, 3 and 4 to pin 5 which presses against the eyeball. Hand b, indicating the pressure on the eyeball, is actuated, when weight A descends, through links 2, 6 and 7, segment gear k and pinion 8. If pin 5 is in proper contact with point d of link 4 when the instrument is placed on the eyeball, then check hand 9 begins to deviate together with hand b. If check hand 9 begins to deviate later than hand b, then the motion of weight A, indicated by hand b, is idle up to the instant hand 9 begins to deviate, and is not to be taken into account. Pin f serves to limit the amount the weight can be raised by pin e.
$1775$GL,M$