BAROMETER.
Recognizing the importance of measuring very accurately the barometric pressure, or at least its fluctuations, we have installed an accurate barometer of the Fortin type, made by Henry J. Green. This is attached to the inner wall of the calorimeter laboratory, and since the calorimeter laboratory is held at a constant temperature, temperature corrections are unnecessary, for we have here to deal not so much with the accurate measurement of the actual pressure as with the accurate measurement of differences in pressure. For convenience in reading, the ivory needle at the base of the instrument and the meniscus are well illuminated with electric lamps behind a white screen, and a small lamp illuminates the vernier. The barometer can be read to 0.05 millimeter.