TONOMETER

n. To2n-oam'e2t-u6r. From TOCOS, tension, and niTpov, a measure. Fr., to no metre. Ger., T. An instrument for estimating tension, especially the tension of the eyeball or the pre ure of the ventricles. [K.] Dors and Lecoultre's t. A t. constructed on the same principle as Harner's t., but having the position of the peg regulated by a screw. The spiral spring is replaced by a straight steel spring, which is not very long, so that the tension rapidly increases with the deep pushing of the peg. [F.] Graefe's t. A t. consisting of a small rod which is pre ed against the eye by means of a loaded lever. A scale shows the degree to which the peg or style can overcome the tension of the eye with various degrees of loading. [F.] Hamer's t. A t. consisting of a metallic tube out of which a peg or style projects. The latter is connected with a wound-up watch-spring, so that by pre ing upon the eye it has to overcome the constantly increasing tension. [F.] Monnik's t. A modification of Hamer's t. in which the immovable tube is replaced by two pegs, which can be pushed in with the slightest po ible friction. The two pegs act together upon an index which shows on a dial-plate the change in position of the two pegs. A second index moves with the middle peg, which is under the increasing pre ure of a short spring. [F.] Roy's t. A t. for estimating the varying pre ure of the ventricles during contraction and dilatation. It consists e entially of an air-tight tube containing oil, in which works a cylinder carrying a registering index. [K, 19.] Verlaan's t. A t. consisting of a tube in which three isolated pegs can be pushed in or out. The middle peg is connected with a spiral spring the tension-power of which increases with the pre ure. The two outer pegs may be moved with the slightest po ible friction, and carry scales which run on a vernier connected with the middle peg. [F.] Weber's t. A t. consisting of a peg which acts with increasing spring power on the sclerotic until its curvature to a certain extent is flattened to a plane. [F.] [s. 631]