Page:Mind (Old Series) Volume 11.djvu/226

 THE TIME TAKEN UP BY CEREBRAL OPERATIONS. 225 copper wire w, one side longer than the other, is fastened to the screen, as shown in the figure. When the screen falls the amalgamated points run into two holes bored in the base and filled with mercury. These basins are connected with the binding screws h h, and these respectively with the battery and chronoscope, so that the current is interrupted at this point. When the screen falls, however, the copper wire connects the two basins of mercury, and the apparatus is so adjusted that the instant (to ToVu se c.) the object on the card is uncovered to the observer, the shorter limb of the wire touches the mercury and the current controlling the chronoscope is closed. This method is in every way better than that hitherto used of illumining the object by an electric light. It avoids altogether the great inconvenience and difficulty of using an induced current, as keeping the light constant, closing simultaneously an induced and galvanic current and otner difficulties best known to those who have tried to overcome them. Further, it eliminates the time required to adapt the eye to a light of un- expected intensity, placed by experimenters as quite large. Lastly, it enables the observer to fixate exactly the point at which the object appears, so that words, &c., can be used. Three instruments were used to break the current controlling the chronoscope at the instant the observer made a motion. The first of these was a telegraphic key, which the observer held closed with his finger or fingers, and let go by a motion of the hand. The key used should be very sensitive ; it should break the current instantaneously, yet should not require much pressure to hold it closed. The other two instru- ments were devised to break the current when the organs of speech are moved. The first of these (Fig. 4) we can call a lip-key. The binding screws FIG. 4. B B are connected respectively with the battery and the chronoscope. The platinum contact at c is closed when the observer holds the ivory tips T T between his lips ; but as soon as the lips are moved the spring S breaks the contact, and, consequently, the current which had been flowing through the chronoscope. The only difficulty in the way of using this lip-key is that it is possible for the observer to move his lips before he makes the motion to be registered. This difficulty is avoided by means of the appa- ratus shown in Figures 5, 6 and 7, which we can call a sound-key. The current controlling the chronoscope is broken when the observer speaks into the mouth-piece M (Fig. 5). An additional galvanic current is needed to work this apparatus. I used four Daniel cells. The current flowed through a commutator (G", Fig. 8), the coil of the electromagnet {Fig. 7), and the instrument shown in Figures 5 and 6. This latter consists of a mouth-piece, a funnel, and a ring (Fig. 6) fitting into the