[clark] 



VISCOSITY OF ETHYL ETHER 



47 



for supporting the cylinder. The cylinder hangs on a fine hard drawn 

 silver wire about 5 cm. long and -05 mm. in diameter. The upper end 

 of this wire is attached to a second hook which is fastened to a spring 

 band of platinum as shown and whose elasticity holds it in place 

 inside the tube. This entire system is placed in one leg of a thick 

 walled glass tube made in the form of an inverted U. The apparatus 

 will be clear from Figure 1. It will be seen that the gold cylinder is 

 suspended concentrically within the cylindrical tube. The glass tube 



Fig. 1. 



is supported in a frame made of thin sheet copper which carries in 

 addition to the tube, two coils of copper wire whose common axis is 

 horizontal and on a level with the iron plug in the gold cylinder. 

 If a current is sent through the coils the iron plug sets itself along their 

 axis and when the current is broken the cylinder oscillates under the 

 combined effects of its inertia and the elasticity of the torsion wire, 

 until brought to rest by the viscosity of the substance in which it 

 hangs. The two legs of the inverted U are partly surrounded by coils 

 of German silver wire so that the liquid in the tube may be distilled 

 from one leg of the tube to the other. In this way observations of 

 the decrement in either the liquid or the vapour are made possible 

 without disturbing the apparatus. The coil on the leg containing the 

 cylinder is open in the middle portion so that the motion of the cylinder 

 may be followed. The four wires for these heating coils and for 

 the directing coils pass out through the bottom of the heater in glass 

 tubes and are connected to a storage battery through three keys. 

 The layers of wire in the directing coil are insulated from each other 



