158 LECTURES. 



fresli supply. This heating apparatus was preferred to the high tem- 

 perature stove and the steam pipe wherever a mild and continuous 

 heat was desirable, and where it was not required to carry the pipes 

 or apparatus containing the water to a very high level, the strain 

 upon the joints of the apparatus being in proportion to the altitude of 

 the column of water they contained. The water could be maintained 

 continuously at any required temperature under 212°. Gas stoves 

 had been introduced in many places with advantage where a small 

 chamber was to be heated, and where there was no convenience for 

 any other arrangement. A most pernicious practice was, however, 

 prevalent where they were used, the products of combustion being 

 permitted to mingle with the air of respiration in apartments not pro- 

 vided with ventilation. Thousands upon thousands sufiered annu- 

 ally where gas lights or stoves not ventilated formed the only source 

 of warmth. 



Dr. Eeid then pointed out the comparatively ineffective results that 

 arose from the action of heating apparatus that conveyed warm air too 

 quickly to the ceiling of the rooms instead of distributing its power 

 on or near the floor. Eailroad cars frequently presented a tempera- 

 ture above 212° at the ceiling, while on the floor the thermometer 

 might be down to the freezing point. They gave an extreme illus- 

 tration of numerous buildings where the introduction of arrangements 

 for securing the full action of warm air at a lower level would add 

 equally to comfort and to economy. The peculiarities of external 

 warmth arising from the rays of the sun were then contrasted with 

 that developed by artificial means. Saussure made an experiment in 

 which air had been raised to a temperature of 210° by merely ex- 

 posing a cork case with glass cover to the direct rays of the sun, and 

 preventing the cooling influence of the circumambient air. The rays 

 of the sun did not directly warm the air, but the ground, from which 

 heat was transmitted to the air resting upon it. In the torrid zone it 

 would probably be practicable, even without the use of lenses or 

 reflectors, to develop heat sufficient to produce a limited amount of 

 steam. A patent had lately been taken out for concentrating the rays 

 of the sun upon boilers in such climates. The great practical lesson 

 which all these points taught was that we should endeavor to warm 

 the lower stratum of air effectually in individual buildings. If this 

 primary point be secured, the upper portion will soon acquire the 

 necessary temjierature from the natural ascent of warm air. 



The cooling of air was in some countries, and at particular seasons, 

 as important a question as the warming of air in tem[)erate and cold 

 climates. In India habitations were sometimes built under ground, 

 the family occupying a lower and lower flat or series of apartments as 

 the external heat iru^reascd. The construction of buildings so as to 

 take full advantage of the shade, and of the basement in making 

 channels of snp[)ly, was seldom made a sufficient object of attention. 

 Tlie production of cold by the evaporation of water was largely intro- 

 duced in many places with advantage ; but where the air was highly 

 charged with moisture this method was disadvantageous, tending to 

 saturate it to' an extent that interfered with the natural exhalation 

 and evaporation from the surface of the lungs and of the body. By 



