656 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



poured into the annular space between, through a small hole in the iron 

 ring. This makes the ends air tight, so that the tube can be exhausted 

 and the liquid drawn in without any moist or dusty outside air. 



Connections. — Ground joints in the enamelled lava bushings admit 

 the side-tubes connecting with the supply of carbon bisulphide and with 

 a filter-pump. A three-way glass stopcock permits the exhaust to be 



Figure 4. Section of the Tube showing Method of Closing Ends. 



A, Tube in longitudinal section, with glass plate against right-hand end. 



B, Cast-iron ring bolted against end, pressing rubber ring, shown in section, 

 against glass plate. Notice small vertical duct in ring through which mercury is 

 poured in to fill annular space enclosed around edge of glass plate by rubber ring 

 shown in section as wired down to flange of iron ring and to tube. 



C, " Lava " bushing, hollow, for 6ide tube admitting liquid and electrical con- 

 nection to electrodes in tube. 



closed and air to be admitted through drying tubes of phosphoric pen- 

 toxide when the liquid used in the observing tube is to be run back into 

 its reservoir. The battery connections are made through platinum 

 wires sealed into glass stoppers ground to fit the other lava bushings, 

 and all these connections are also mercury-sealed. 



Advantage is taken of two of these side outlets to insert permanently, 

 at the upper and lower ends of the tube, two small mercury thermome- 

 ters which can be read through the glass side-tubes. 



