Examination of the instrument would suggest that it is splash proof but has no long-term, weather resistant properties. It is thus unlikely to be intended for permanent set-up out of doors for meteorological purposes.
Its remarkable sensitivity might suggest a mine ventilation measuring device but even this seems unlikely. The instrument was obtained from an ex-govt source which specialising in ex-military hardware. Yet the case is not painted green nor covered in typical heavy military symbols or codes.
It came in a neat, plywood, protective case.The lid contains a graph for defining average wind speed against rotor revolutions.
The rough piece of 18mm plywood is only a temporary base to allow the instrument to stand up safely for photography.
The base casting would normally fit in the empty spring clip on the left inside the case.
Note the neat clamps and compact arrangement of the instrument within the case. There is no obvious sign in or on the case to which this base casting might have been affixed.
Here the instrument has been removed from the case to show the taper to the bottom of bearing shaft. This fits in a matching taper in the base casting.
The number on the rear of the dial and the source suggests that the instrument was used to measure wind speed for military gunnery control.
The carrying handle and manufacturer's label.
The instrument set up on the temporary plywood base.
The overcast weather conditions make for shadowless photography but the exposure is too long to capture the rotating cups sharply. The cups rotate freely in only a breath of air movement. Often too light to sense with bare forearms.
The Casella counter dial reads directly to 100 revolutions. Sub dials read in 100s and 1000s of revolutions. Useful for longer duration measurements.
The shaft-gripping collet inside the rotor head is clearly seen here.
Here is the point on top of the stainless steel shaft where the rotor sits.
Here is a scan of the original Casella graph sheet. I have added the axes text to the image for clarity. The original axes labels were handwritten.
An older video of the Casella anemometer in action:
Further to my rather wild guesses above I found another Casella for sale with rather more original information. The Casella 'Sensitive' Anemometer was intended for recording low wind speeds or air movement. It could be used to check industrial and mine ventilation. It was also used in aeronautics. The Counter/Air Velocity graph above only rises to 30 fps which is about 9 m/s, 30kph or 20mph. Hardly suitable for normal weather measurement. Thanks to its jewelled, low friction main shaft bearings and low inertia it started at very low air velocities compared to the much larger and heavier Casella/Munro MkII meteorological type of anemometer.
Click on any image for an enlargement.
