y be substituted by a more substantial
instrument. The form of resistance using small lamps and the resistance
wires wound on asbestos lumber has proven very satisfactory and very
compact in form.

[Illustration: FIG. 18.--Diagram of rheostat and resistances in series
with it. At the right are shown the sliding contacts, and in the center
places for lamps used as resistances, and to left the sections of wire
resistances.]

TEMPERATURE RECORDER.

The numerous electrical, thermometric, and chemical measurements
necessary in the full conduct of an experiment with the respiration
calorimeter has often raised the question of the desirability of making
at least a portion of these observations more or less automatic. This
seems particularly feasible with the observations ordinarily recorded by
the physical observer. These observations consist of the reading of the
mercurial thermometers indicating the temperatures of the ingoing and
outcoming water, records with the electric-resistance thermometers for
the temperature of the air and the walls and the body temperatures, and
the deflections of the thermo-electric elements.

Numerous plans have been proposed for rendering automatic some of these
observations, as well as the control of the heating and cooling of the
air-circuits. Obviously, such a record of temperature measurements would
have two distinct advantages: (1) in giving an accurate graphic record
which would be permanent and in which the influence of the personal
equation would be eliminated; (2) while the physical observer at present
has much less to do than with the earlier form of apparatus, it would
materially lighten his labors and thereby tend to minimize errors in the
other observations.

The development of the thread recorder and the photographic registration
apparatus in recent years led to the belief that we could employ similar
apparatus in connection with our investigations in this laboratory. To
this end a number of accurate electrical measuring instruments were
purchased, and after a number of tests it was considered feasible to
record automatically the temperature differences of the ingoing and
outcoming water from the calorimeter. Based upon our preliminary tests,
the Leeds & Northrup Company of Philadelphia, whose experience with such
problems is very extended, were commissioned to construct an apparatus
to meet the requirements of the respiration calorimeter. The conditions
to be met by this ap