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shoes, or by throwing an enlarged image of the wire on to a screen by means of an arc lamp and projection lantern. The instrument is extremely sensitive, very dead beat, has a very short period and is practically without self-induction or capacity. Used in conjunction with a photographic recording apparatus it will record alternating or pulsating currents of very small magnitude, or their variations may be observed visually in a rotating mirror. The instrument is extremely valuable in physiological investigations and was in fact developed by Prof. Einthoven mainly for this purpose.

The period depends entirely on the tension of the fibre which is adjusted by means of the micrometer screw J (Fig. 4). With a moderate tension, however, the period is extremely quick, and, by increasing the tension, may usually be reduced to less than ! ^0 second. In practice the limiting condition here is the damping. If the tension is increased too much the instrument ceases to be aperiodic and “overshooting” occurs. The shortness of the period is due to the exceedingly small weight and inertia of the fibre. Its weight is approximately 10“6 gramme. If the tension is relaxed the fibre may take several seconds to attain its full deflection with a consequent gain in sensitivity. The indefinite increase of period by slackening the fibre is however in practice limited by unsteadiness of zero and by the fact that, when very slack, the fibre moves out of focus when deflected.

The galvanometer is quite dead beat over a wide range, the damping being partly electro-magnetic and partly due to air friction. The electro-magnetic damping may be varied by altering the strength of the magnetic field and the resistance in circuit with the fibre. The damping may also be controlled by means of a suitable arrangement of capacity and inductance in circuit.

The arrangement of the optical system depends on whether the deflections of the fibre are:—

(a) being observed by means of a microscope (with micrometer eye-piece) ; (6) being projected on to a screen by means of an arc lantern; (c) being recorded photographically.

Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,43 %.

La langue de reconnaissance de l'OCR est l'Anglais.