Glass Enclosed Spark Gap

A vintage glass enclosed spark gap. The gap distance is adjustable from the top. Has an additional side glass tube of unknown purpose (vacuum, exhaust, ??). This has the feel of an early electrical instrument rather than spark wireless but it is unclear. There are no makers marks of any kind. 10.25" high (bottom of base to top of upper brass cap - not including upper gap element) and glass tube approximately 1.625" diameter.