THE CALORIMETER. 21 



tion of heat. In order to allow the absorber system to be removed, added to, 

 or repaired at any time, it is necessary to insert couplings at several points. 

 This is usually done at corners where the attachment of disks is not prac- 

 ticable. The total length of heat-absorbers is 5.6 meters and a rough calcu- 

 lation shows that the total area of metal for the absorption of heat is 4.7 

 square meters. The total volume of water in the absorbers is 254 cubic 

 centimeters. 



It has been found advantageous to place a simple apparatus to mix the 

 water in the water-cooling circuit at a point just before the water leaves 

 the chamber. This water-mixer consists of a 15-centimeter length of stand- 

 ard 1-inch pipe with a cap at each end. Through each of these caps there 

 is a piece of one-eighth-inch pipe which extends nearly the whole length of 

 the mixer. The water thus passing into one end returns inside the 1-inch 

 pipe and leaves from the other. This simple device insures a thorough 

 mixing. 



The air-pipes are of thin brass, 1-inch internal diameter. One of them 

 conducts the air from the ingoing air-pipe up into the top of the central 

 dome or hood immediately above the head of the subject. The air thus 

 enters the chamber through a pipe running longitudinally along the top 

 of the dome. On the upper side of this pipe a number of holes have been 

 drilled so as to have the air-current directed upwards rather than down 

 against the head of the subject. With this arrangement no difficulties are 

 experienced with uncomfortable drafts and although the air enters the 

 chamber through this pipe absolutely dry, there is no uncomfortable sensa- 

 tion of extreme dryness in the air taken in at the nostrils, nor is the absorp- 

 tion of water from the skin of the face, head, or neck great enough to pro- 

 duce an uncomfortable feeling of cold. The other air-pipe, as suggested, 

 receives the air from the chamber at the lower front and passes around the 

 rear to the point where the outside air-pipe leaves the chamber. 



The chamber is illuminated by a small glass door in the food aperture. 

 This is a so-called " port " used on vessels. Sufficient light passes through 

 this glass to enable the subject to see inside the calorimeter without diffi- 

 culty and most of the subjects can read with comfort. If an electric light 

 is placed outside of the window, the illumination is very satisfactory and 

 repeated tests have shown that no measurable amount of heat passes through 

 the window by placing a 32 c. p. electric lamp 0.5 meter from the food 

 aperture outside. More recently we have arranged to produce directly 

 inside the chamber illumination by means of a small tungsten electric lamp 

 connected to the storage battery outside of the chamber. This lamp is 

 provided with a powerful mirror and a glass shade, so that the light is very 

 bright throughout the chamber and is satisfactory for reading. It is neces- 

 sary, however, to make a correction for the heat developed, amounting 

 usually to not far from 3 calories per hour. 



