  Rubidium time standard exciter. 
This is a small bulb that, in the original device, was positioned next the cell shown in the previous sample.  It is, I am told, filled with a larger amount of rubidium than the larger cell, and serves as the the exciter, transmitting radio waves of the correct frequency to excite the lower-pressure rubidium vapor in the larger cell.  (Lower pressure means narrower spectral line, and thus higher accuracy.) 
Source: eBay seller nhbbobb1985 
Contributor: Theodore Gray 
Acquired: 19 November, 2008 
Text Updated: 10 January, 2009 
Price: $38 
Size: 0.75" 
Purity: 99.9%
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