Refraction for Electric Waves. 



magnet to the thermal-junction is 6*7 centim. 

 pieces are 4 millim. apart. 



An idea of the suspension can be had from fig. 

 a section through the axis of the 

 field-magnet (M, M). The^ coil 

 consists of a single loop, 2 millim. 

 wide, of number 34 B & S silk- 

 covered copper wire. After form- 

 ing the loop, the ends of the wire 

 are twisted together for a distance 

 of about 5 5 centim. downward, and 

 are then separated to form the ter- 

 minals a, a. The resonating system 

 consists of two copper cylinders, 

 o, o, 8 millim. long and 1 millim. in 

 diameter. These cylinders are about 

 1 millim. apart, and to their nearer 

 ends are soldered respectively a con- 

 stantan and a manganin wire re- 

 duced by aqua regia to have a diame- 

 ter o£ '01 or '02 millim. These small 

 wires are crossed at K, conveyed 

 off at right angles and soldered to 

 the leads a, a, thus forming a closed 

 circuit with the coil. The resona- 

 tors o, o are sewed by silk threads 



181 

 The pole- 



3, which is 



Fie:. 3. 



to a mica vane, 



v, 



the leading 



and 

 wires are fastened to the vane by 

 sealing-wax at W. The springiness of the leads keeps the 

 finer wires in contact at K. 



When electric waves of proper length enter the cavity, R, 

 they are made to converge by the reflector and cause electric 

 surging up and down between the cylinders o, o, heating 

 the thermal-junction K and producing a steady current 

 through the coil. Being in a strong magnetic field, the coil 

 turns so that its plane makes a small angle with the axis of 

 the magnet. These small deflexions are read by an Elliot 

 reading- telescope of such good definition that tenths of a 

 millimetre can be estimated with considerable accuracy. 



To protect the thermal-junction from outside thermal dis- 

 turbances, the magnet, the back of the reflector, and the 

 suspension-tube are covered by wood 3 centim. thick ; the 

 opening of the reflector is closed by a sheet of cotton-wool of 

 about the same thickness ; and the whole instrument is then 

 put under a pile of felt 5 or 6 centim. thick. The only part 

 that is at all exposed is the mirror of the suspension, which is 



