Franklin's or Mascart's Flask
 Mascart's Flask is a device for providing a great deal of electrical insulation for quadrant electrometers used to measure electrical potentials in situations in which essentially zero current is drawn from the system under test. An example is the measurement of atmospheric electric potentials.
  The late 19th century flyer for Mascart's electrometer, published by Rhumkorff, shows three of the flasks supporting the electrometer and one flask holding up an antenna. 

   The two flasks illustrated (Denison University at the left and the Smithsonian Institution at the right) were photographed inverted; when I took the pictures I did not not know how the device was used. 
 
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