INCREASE IN SIZE. 



103 



whole is to be covered with a thin coat of shellac to prevent warp- 

 ing. A support for the wheel is made by fixing (with sealing-wax if 

 necessary) a perfectly bright slightly- vaselined needle in a piece of 

 capillary tubing, and the wheel should turn freely upon it ; the 



1 



FIG. 24. AN AUTOGRAPHIC AUXANOMETER. FIG. 25. M.v< ;MFYIN<;- WHEEL, 

 (As here shown, the pen is much too large.) IN SECTION. One-halt" the 

 One-third the true size. true size. 



tubing is then to be supported horizontally on a tripod support 

 with the wheel vertical. A recording-pen is to be prepared from 

 small glass tubing drawn to a capillary point and bent at right angles 

 as shown in Fig. 24 (though it should be of much smaller size than 

 there shown) ; it is held in a loop of flexible brass to which a thread 

 can be attached ; into the pen a few drops of chronograph ink are 

 drawn. Set the wheel with one edge over the cylinder, and the other 



