A rare ‘stretched wire’ telemeter described by the military
surveyor Col. Goulier in 1868* and made by Tavernier Gravet
of Paris. The wire base line connects the two hand held
instruments that each contain a prism, one of which moves over
a graduated scale. The observers see each other and an
inaccessible object whose distance is indicated on the scale.
Condition is good (loss of silvering to the casing).
Ticket Price: £450.
A dewpoint (condensation) hygrometer of the type described
In 1820* by John Frederic Daniell (1790 - 1845). In use,
ether is dropped on the bulb covered with cloth. The other
bulb contains a thermometer and some ether, the rest of the
space is a vacuum. Ether evaporating from the cloth causes
The instrument to cool. Moisture then condenses from the
atmosphere onto the gilded bulb. By noting the temperature
when this happens and the ambient temperature the amount
of moisture in the atmosphere can be determined.
Engraved “SECRETAN A PARIS”. French c.1860.
Ticket Price: £580.
Larger photograph
-13.jpg "Stretched wire telemeter")
