PSYCHOLOGICAL APPABATUS. oOIt PSYCHOLOGICAL APPARATUS. tion table, a llat bed or lalile upon which the obseier is stretched, and which can be twirled round, in the horizontal plane, at constant rates. Perception of the movement and position of the whole body is investigated both by the rotation table, and by the lilt-hoard, a similar instrument, in which the table can be swunj; throujjh approxi- mately 180° in the vertical plane. The observer, strapped upon the table, estimates the extent and direction of movement, the true values of which can be read from a scale. Taste akd Smell. For the study of gustatory sensation, we need very simple api)liances: a magnifying glass or concave (enlarging) mirror, for bringing out clearly the separate papilhe of the tongue; fine camel's-hair brushes, for the application of stimulus; and sets of solutions, of varying strength — sweet (sugar), salt, sour (tartaric acid), and bitter ( hydrochlorate of quinine). For the study of olfactory sensation, on the other hand, we need a special (and in some of its forms highly complicated) instru- ment, the olfactometer of Zwaardemaker. In principle, the olfactometer consists of a glass tube, bent up at right angles to enter the ob- server's nostril, and passing through an odorless screen of wood or metal, which prevents the access of any foreign odor to the nose. Over the portion of the tube that projects behind the screen is slipped an 'olfactory cylinder' — a glass cased tube of some odorous matter, such as rose- wood or asaftetida. When the cylinder is pushed hard against the screen, its outer edge is flush with the end of the glass inhaling tube, so that nothing of its substance can be smelled. If, however, it be pulled out. say for 1 centimeter, then the current of air which reaches the ob- server's nostril must pass over this 1 centimeter of exposed odorous surface before it enters the inhaling tube. If the cylinder be pulled out still farther, then the incoming air current must pass over a still greater odorous surface. We have, in this way, a means of quantitatively regulating the stimulus that we are applying to the sense organ. AFFECxm: 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 ) 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 or 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 dnmi moves and the fork vibrates, the movement of the strip will be drawn out into a sinuous curve, each wave of which represents the time unit of the vibrating prong. The cun-e shows white upon the drum surface, since the moving strip knocks off the soot at the point of contact. Finally. (3) 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. If we press the clastic 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 and fall correspondingly, and we have our curve traced upon the kymograph. The funnels are known as Marcy's tambours. In the Hphyg- mograph, or pulse recorder, the free tambour is laid over the radial artery of the wrist, and the pulsations of the artery arc repro- duced upon the drum. In the pneumograph, or breathing recorder, this tambour is replaced by an clastic girdle, passed round the thorax: this opens into the connecting rubber tul)e. and the curve is traced as before. In the plethysmo- 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 member changes in volume, the writing point rises and falls upon the kymograph sur- face. Lastly, in the dynamograph, or strength recorder, the free tambour is replaced by a heavy steel spring, which is gripj)ed by the hand; as the pressure increases or relaxes, puffs of air are sent along the connecting tube to the writing lever, and the fluctuations of muscular strength are correctly registered. It is also necessary to record the invoUmtary movements of arm and hand. For this j)urpose we use the automato- graph, a scientific modification of the once popu- lar planchette. The course of fatigue may be followed by means of the ergograph, which re- cords the work done in a continuous pull against a spring, or in the successive lifting of a constant weight. AcTiox. The simplest instrument for the per- formance of reaction experiments (see Re.c- TIOX) is Sanford's vernier chronoscope. This consists of two pendulums, of slightly different lengths. The one is started by the opening of a key, simultaneously with the giving of the stimu- lus (the signal for movement) ; the other, bv the opening of a .second key, pressure upon the but- ton of which constitutes the nmvement of reac- tion. The two pendulums swing together on the principle of the vernier; and the number of swings made: before coincidence is reached, gives the reaction time in fiftieths of a second. A more elaborate arrangement is that of the Eipp chronoscope. This is an electric clock, with a unit of a thousandth of a second. The clock is started by the giving of the reaction stinuilus, and arrested by the reaction movement. The stimulus may be given by the swing of a pendu- lum, which sends a ray of light or exposes a patch of color to the observer's eye; by the fall of a hanuucr upon a metal block; by a pressure upon the skin. In every case, the instrument employed is in electrical connection with the chronoscope. The movement of reaction may be made l)y hand or foot, by voice, by lips, or eyelid. Whatever the form of 'reaction key' employed, it, too, is always in electric connection with the chronoscope. Once more, the time of reaction may be recorded directly, by time-markers, upon the surface of the chronograph, a kind of kymo- graph, provided with tuning-fork controls that give an exceedingly accurate time line.
