In continuation of the paper read before the American Institute of Architects, i which has appeared in the three previous numbers of this JOURNAL, it is desirable to support the argument for the impracticability of attaining the full summer eondi'tion of humidity, for air in winter which has been warmed to the temperature of comfort, by more extended computations than could be presented to an audience, or brought within the scope of comprehension of the listener or the casual reader. The single example with specified relations, which was taken, showed, on calculation, that nearly as much heat would be expended in supplying vapor for the usual hydration of air of usual humidity and of 34 ยฐ temperature (which air was heated to 70ยฐ), as was expended in heating the air itself,
The temperatures, and humid condition of about 69 per cent. assumed, being the averages of nature, out of doors, for three warm or three cold months, in the city of Philadelphia, in 1844, as reported by Prof. Bache. It occurs, accidentally, that the exact conditions of temperature and humidity chosen for an example, give the ratio of heat demanded for the two purposes incident to warming air as unity, while this ratio, for other temperatures and degrees of humidity, will be found to vary materially. For the purpose of exhibiting more completely the general case, the accompanying table has been prepared to show what quantities of heat are demanded for heating, or are given out in cooling air of 70 per. cent. humidity, from various temperatures (from 0 ยฐ to 100 ยฐ) to 70 ยฐ, in direct comparison to the quantities for vaporization or condensation of water to procure the condition of 70 per cent. humidity to the air of 70 ยฐ. When 70 ยฐ and 70 per cent. humidity may be accepted as the American summer condition of comfort for the air; it being asserted that 70 ยฐ, with 80 per cent., or more, of humidity, is close and enervating, while 70 ยฐ , with 60 per cent., or less, of humidity, is fresh and cool, and demands heavy clothing to preserve the comfort of the individual--a proper and necessary demand in winter.