CHAFFEE. — IMPACT EXCITATION OF ELECTRIC OSCILLATIONS. 271 



however, for over one hundred hours with fairly satisfactory results at 

 the expiration of that time. 



Several metals work well as anode, the latter apparently playing 

 very little part in the action of the gap. It appears, however, that 

 the denser metals of high cathode drop, such as copper and silver, are 

 desirable. The anode, with occasional cleaning, will serve indefinitely. 



Although the amount of heat produced in the gap is small, some 



FiGUKE 2. Details of Water-cooled Cii-Al Gap. f natural size. 



method of cooling the terminals is necessary. Air cooling by means 

 of radiating vanes is to be preferred on account of convenience and 

 simplicity. Figure 1 gives the details of an air-cooled gap, the right- 

 hand half in section. At e there is shown the Al electrode which is 

 held by a taper-fit in the massive terminal t. Opposed to this Al elec- 

 trode is a similarly shaped copper electrode held by taper-fit in a similar 

 massive terminal. These terminals are threaded and engage in the 

 side castings cc, and are provided with blackened metallic radiating 

 vanes as shown. The side castings are separated by a thin slab of 

 hard rubber or asbestos board, which has a central circular hole to 

 serve for the gap chamber h. Rubber handles rr are for use in ad- 

 justment. The inlet and outlet for the hydrogen are shown at i and o. 

 The drawing is one half size. 



