228 J. M. CATTELL : The pressure is kept constant by regulating the strength of the spring F. It will be seen that after the contact in the funnel is broken, no appreciable time elapses before the current controlling the chronoscope is broken ; but the contact in the funnel is broken by the slightest motion of the speech- organs, so the instant of this motion is registered. In Fig. 8 I give the arrangement of the apparatus when it is wished to determine, for example, the time it takes to see and name a word. It is a matter of no small importance so to arrange the apparatus that it can be con- veniently operated on, and the figure will further make clear the connexion of the different instruments and the several batteries. The observer sits at A., the light coming over his left shoulder. His head is held naturally, and at the distance of most distinct vision for the word. He can conveniently speak into the mouth-piece of the sound-key F, or hold the telegraphic key at K closed. The experimenter 1 sits at B., within easy reach of all the apparatus he has to control. The current belonging to the chronoscope flows from the positive pole of the battery B to the commutator C, thence through the rheostat R K (if desired, also through the electrometer E) and chronoscope Ch to the gravity-chronometer G, where the connexion is interrupted when the mercury in the two basins is not connected, thence the current flows through the contact of the sound-key at F back to the commutator and battery. The current making the electromagnet of the gravity-chronometer flows from the battery B to the commutator (7, and thence through the key K" and the gravity-chronometer back to the commutator and battery. The third current, controlling the sound-key, flows from the battery B" to the commutator C"', and thence through the contact of the sound-key at F and coil of the magnet at S, and back to the commutator and battery. Suppose now we wish to measure the time it takes to see and name a word. The experimenter puts a card on which a word is printed into the springs of the gravity-chronometer ; he then says 'now, and starts the clockwork of the chronoscope. The observer fixates the point on the screen immediately before the word. Then the experi- menter (or the observer himself) allows the screen to fall by breaking the current which, through the electromagnet, had been holding it up. Sud- denly the word appears at the point fixated by the observer, and at the same instant the basins of mercury are connected by the copper wire ; thus the current controlling the chronoscope is closed and the hands are set in motion. The observer names the word as quickly as possible. As soon as he begins 1< speak, the current making the magnet at N is broken and the armature is drawn away. The current controlling the chronoscope is thus broken, and the hands stand still. The experimenter then stops the clockwork and reads from the dials the exact time taken to see and name the word. The special methods and precautions necessary to secure correct results in using the apparatus here described can best be considered when I corne to treat of the different cerebral opera- tions, the times of which I have tried to determine. It may, however, be well to mention here two points, which are common to all the experiments I have made. The first of these is the method of deducing a correct average from the separate experi- ments. Two methods have been employed : either all the re- 1 I call the person having charge of the apparatus the experimenter ; the person on whom the experiments were made the observer.
