f the tension-equalizer
completely from the rest of the system at the exact moment of the end of
the experimental period. After the motor has been stopped and the slight
amount of air partly compressed in the blower has leaked back into the
system, and the whole system is momentarily at equal tension, a process
occupying some 3 or 4 seconds, the gate-valve H is closed. Oxygen is
then admitted from the pet-cock K until there is a definite volume in J
as measured by the height to which the diaphragm can rise or a second
pet-cock is connected to the can I and a delicate petroleum manometer
attached in such a manner that the diaphragm can be filled to exactly
the same tension each time. Under these conditions, therefore,
the apparent volume of air in the system, exclusive of the
tension-equalizer, is always the same, since it is confined by the rigid
walls of the calorimeter and the piping. Furthermore, the apparent
volume of air in the tension-equalizer is arbitrarily adjusted to be the
same amount at the end of each period by closing the valve and
introducing oxygen until the tension is the same.

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.

ANALYSIS OF RESIDUAL AIR.

The carbon-dioxide production, water-vapor elimination, and oxygen
absorption of the subject during 1 or 2 hour periods are recorded in a
general way by the amounts of carbon dioxide and water-vapor absorbed by
the purifying vessels and the loss of weight of the oxygen cylinder;
but, as a matter of fact, there may be considerable fluctuations in the
amounts of carbon dioxide and water-vapor and particularly oxygen in the
large volume of residual air inside the chamber. With carbon dioxide and
water-vapor this is not as noticeab