mercurial thermometers made by Geissler and calibrated by the Phys¬
ikalische Technische Reichsanstalt. In construction they are very
similar to the ordinary Beckmann thermometer and are bent at right
angles like the bent thermometers used in the Middletown calorime¬
ter. They have the column calibration of a milk scale and the
mercurial column is in a fine capillary tube inside of a glass
envelope. They are very long and fragile and very hard to trans¬
port, although Prof. Hagemann has had two sets shipped to Berlin
nd returned without being broken. Special transportation cases
were made for them. They were graduated from -1.0° to -+20.0° in
l/l00th degrees.
The method of reading the thermometers is very ingenious and
worth copying. Two telescopes are mounted on a sliding rod.
These are adjusted with two mirrors so that there is a maximum
illumination of the mercurial column, a great convenience in
reading. Naturally, the use of the telescope also avoids the
errors of parallax. The only objection is that the telescope
'MSMT
must be focused each time by each observer.
z'