These items that are sometimes mistaken for lightning rod insulators are actually a patented valve seat for a hand pump! They are incuse marked "MYERS PATENT / 3" The patent was US Patent #282755 issued to a Philip Myers on August 7th, 1883 and assigned to a Francis E. Myers both of Ashland,
A similar item has been found with the patent date incuse marked in the glass:
Claim 9 of the patent reads: "In combination with the pump-cylinder having the valve, the cap f, provided with the chamber, a glass seat fitted to said chamber, and suitable packing, all substantially as described."
Thanks to Jim Colburn for uncovering this information!
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