264 OUR PHYSICAL WORLD 



through the base board. The wire nearest the end of the base 

 is fitted into a groove made on the under side of the base and 

 securely connected to the binding-post set in the center of this 

 end of the base. This binding-post receives the ground con- 

 nection. 



The other end of the winding is also led through a hole in the 

 base and along a groove to the under side of the binding-post 

 which carries the cat whisker of the detector. Another style 

 of connection, which may work better in some localities, is 

 that of leaving this end of the coil unconnected, and con- 

 necting this side of the detector directly to the ground binding- 

 post. 



The detector is mounted midway between the end of the coil 

 and the binding-posts for the phones. These phone connections 

 are placed close to the end of the base and midway between the 

 sides so that the strip condenser will be parallel to the end of the 

 base. One of these phone terminals is connected to the crystal 

 of the detector and the other to the slider mounted on the side of 

 the coil. The connection wire is to be led through a groove on 

 the under side of the base to a hole directly under the binding- 

 post on the slider rod. The slider rod on the slide is then secured 

 to the ends of the tuning coil on its front side by means of the 

 binding-post in such manner that this binding-post will be on the 

 end nearest the detector. The other slider rod is mounted on 

 top of the coil with its binding-post on the other coil end. This 

 slider is connected to the aerial wire or antenna. 



The phones must be purchased. They may be either single 

 or double. A double head set of 2,000 ohms resistance is recom- 

 mended. When the phone cords are connected to the binding- 

 posts provided, the set is ready for operation as soon as the 

 antenna and ground are connected. 



The ground connection is made with a bare copper wire (about 

 No. 10 or No. 12) to a water-pipe or to a metal plate buried 

 about three or four feet in the earth. If the earth is very dry 

 this plate may have to be buried deeper. 



