THE STRUCTURE OK THE NUCLEUS. 



143 



wide rubber tube EE', of half inci, bo.'e, the ends being secured by ordinary hose 

 couplings to the correspondingly wide stop-cocks, sci'ewed into the lids of AB and 

 C A spiral spring in EE keeps it open. The vessel C is a shorter cylinder than 

 the other, but is also provided with a metallic lid. It communicates with the jet 



b ^ 



Fig. I. — DiKFUiio.N Tciwek, AB; Exuaistiun Cha.mhek, C\ Dksiccator, JJ, and Aiitrtenances. 



pump through the desiccator D, and the filter E", a stop-cock, c, being iuterpo.sed. 

 It is well to provide for an additional stop-cock at the jet pump, which, on being 

 closed, prevents the accidental entrance of water into the connecting pipes. A final 

 stop-cock, d, communicates through a filter witli the air, and is useful \vhen the 

 exhaustion within C, as shown by the gauge G', is larger than desirable. 



The manipulation is as follows: The cocks a, a\ e, d, are closed, Z* and b' 



