AFFECTIVE PROCESSES. Under this heading, we must give a brief general account of the graphic method. The essentials of the method are three in number. We must have 1 I a recording surface. on which the curve is to be traced. This generally takes the form of a brass drum, rotated by weight or motor o• clockwork, and covered with a sheet of smoked white paper. It is called a kymograph. We must have (2) a time line, i.e. a tracing marked off into divisions which represent known time units. We may, e.g. at tach a little strip of parchment to one of the prongs of an electrically driven tuning fork, and lay the tip of this strip tangentially against the revolving drum. As the drum moves and the fork vibrates, the movement of the strip will be drawn out into a sinuous cure, each wave of which represents the time unit of the vibrating prong. The curve shows white upon the drum surface, since the moving strip knocks off the soot at the point of contact. Finally. 1 3 1 we must have special apparatus which shall write upon the drum, above the time line. the course of the process under investigation. Such appa ratus are actuated, for the most part. either by electricity or by air transmission. For example. in registering the course of breathing. we employ air transmission. We connect the stems of two little funnels by a piece of rubber tubing and stretch a sheet of thin rubber over their two heads. It we press the elastic covering of either head, the covering of the other will, evidently, bulge outward. Let us, then, apply the first head to the observer's chest and hinge a light lever (which we apply to the drum surface) to the other. As the chest rises and falls in respiration.
the lever on the second funnel-head will rise mid fall correspondingly, and we have our curve traced upon the kymograph. The funnels are known as Marcy's tambours. In the sphyg mograph, or pulse recorder, the free tambour is laid over the radial artery of the wrist. and the pulsations of the artery are repro duced upon the drum. In the pneumograph, or breathing recorder, this tambour is replaced by an elastic girdle, passed round the thorax: this opens into the connecting rubber tube, and the curve is traced as before. In the ph thysmo graph, or volume recorder, the tambour is re placed by a glass vessel containing air or water. The hand or arm is inserted in the vessel. which is then hermetically closed, save for the tube connection to the writing tambour. As the in closed meinher changes in volume, the Writhig, point rises and falls upon the kymograph sur face. Lastly. in the dyna m ogro ph, or strength recorder, the free tambour is replaced by a heavy steel spring. which is gripped by the hand: as the pressure increases or relaxes, pulls of air are sent along the connecting tube to the writing lever, and the fluctuations of musetmI:o• strength are correctly registered. It is also necessary to record the involuntary movements of arm and hand. For this purpose we use the au tomato graph, a scientific modification of the once popu lar planchette. The course of fatigue may be followed by means of the crgograph, which re cords the work done in a continuous pull against a spring, or in the successive lifting of a constant weight.