1913-14.] Analytical Study of the Mechanism of Writing. 235 
may be regarded as indicating the general lines upon which any such 
apparatus must be constructed. The essential part of the apparatus is 
the arrangement for receiving the grip in such a way as to enable us to 
record its pressure. This is constructed of rubber and is double walled. 
In its construction two teats are used, a large and a small. These are 
placed one inside the other, the space between their walls being filled with 
mercury and sealed. Finally, a narrow glass tube is passed into the inner 
space, and that too is filled with mercury until the mercury stands about 
two inches up the tube. 
To begin with, a single teat was used, but it was found that, immediately 
under the fingers, with a moderately firm pressure, all the mercury was 
expelled, and the rubber sides pressed together. Consequently it was 
impossible to record the full pressure with this arrangement. This defect 
is remedied by the double teat, arrangement with the sealed space between 
Fig. 3. 
the walls. The record of grip pressure is obtained in the usual way by 
connecting the upper end of the glass tube, which projects above the metal 
holding tube, by means of rubber tubing to a recording tambour. 
The most serious defect of this apparatus is its weight, and this is 
largely due to the use of mercury. It might be possible to replace the 
mercury with a lighter liquid, if one could be obtained which neither 
affected the rubber nor evaporated to any great extent from the inner 
space. It is impossible to use merely an air space between the teats, since 
this makes the holding part of the apparatus much too soft and introduces 
thereby a very disturbing factor. 
III. Point Pressure Apparatus. 
The pressure on the writing point itself has already received a con- 
siderable amount of attention, and has been made the basis for several 
interesting discussions, bearing not only on the psychology of writing, but 
also on the study of defective and feeble-minded children, and of the effects 
of drugs like alcohol on the motor co-ordinations in writing. 
Hitherto the apparatus employed to record what is called par excellence 
writing pressure has in every case recorded the pressure on the writing 
surface rather than on the writing point. Kraepelin employed what he 
called a “ Schriftwage,” which consisted of a plate supported by springs 
