132 



SCIENCE. 



[N. S. Vol. XVII. No. 421. 



and the air is unable to carry away mois- 

 ture generated in the laboratory. 



In heating a building by the double- 

 duct system, hot air from one duct is 

 mixed with cooler, tempered air from a 

 second duct in such proportions as to hold 

 the temperature of the room constant, the 

 proportions of the hot and tempered 

 air being regulated by a pair of dampers, 

 the latter being automatically controlled 

 by means of a thermostat. Bach room 

 of a building, therefore, has its own sup- 

 ply flue, regulating dampers and ther- 

 mostat. The latter may be set at any de- 

 sired temperature within the range of the 

 apparatus. If now in hot weather the 

 hot-air duct of winter carries air taken 

 from out of doors, say at 90° F., and the 

 tempered-air duct carries artificially 

 cooled air, say at 60°, a mixture of the 

 two may give a room temperature of 75° 

 when the temperature would otherwise be 

 80° or 85°. And the thermostat will ad- 

 just automatically the proportions of 

 cooled and uncooled air, so as to hold this 

 temperature constant, thus preventing the 

 usual gradual increase of temperature as 

 the day progresses. By a readjustment of 

 the thermostat any other constant tem- 

 perature can be secured, provided it is 

 within the range of the system. 



Not only will this system make possible 

 automatic temperature control in summer 

 — a most important end in itself— but it 

 will also secure a humidity control. For 

 by cooling air its moisture is partly re- 

 moved, and by lowering its temperature 

 to the freezing point it is very largely re- 

 moved. In order to remove as much mois- 

 ture as possible, it is intended to overeool 

 the air and then partly warm it up again, 

 and this may be done economically by 

 means of a heat exchanger, i. e., air on its 

 way to the cooling chamber gives up heat 

 through a thin metal wall to the overcooled 



air coming from the cooling chamber; a 

 given refrigerating capacity will thus re- 

 move the maximum quantity of moisture, 

 so that the percentage humidity of the air 

 may be no greater at the lower room tem- 

 perature than, under normal circum- 

 stances, it would be at the higher tem- 

 perature. 



With this system of heating in winter 

 and cooling in summer, with automatic 

 temperature control the year round, with 

 excess of moisture simultaneously removed 

 by refrigeration, and dust from the fresh 

 air taken out by filters, the double windows 

 of the laboratory will be kept tightly 

 closed in summer as in winter, and an at- 

 mosphere favorable for experimentation 

 may at any time be secured. The closed 

 double windows will also effectually keep 

 out dust and dirt, two of the enemies of 

 the experimentalist. With gas, compressed 

 air, vacuum, hot and cold water, ice water 

 and distilled water always at hand; with 

 cold brine, carbon dioxide and liquid air 

 always available for low temperatures, 

 and gas and electric furnaces available for 

 high temperatures; with direct electric 

 currents, at potentials up to 20,000 volts 

 and currents up to 20,000 amperes, and 

 still higher alternating voltages and larger 

 alternating currents always available, it 

 is believed that the facilities and appli- 

 ances necessary for carrying on a wide 

 range of experiments under favorable con- 

 ditions will be fairly well realized. 



THE MECHANICAL LABORATORY. 



The mechanical laboratory is being built 

 of dark red brick, trimmed with Indiana 

 limestone. It stands on ground sloping 

 toward the north, so that the basement 

 story is wholly above ground on the north, 

 but comes only a few feet above ground on 

 the south. The building is 135 feet long 

 east and Avest, and 48 feet wide north and 



