220 
Relation of Moisture in Air 
[April, 
very small in comparison with what is needed for complete 
“ hydration,” or even for what can be denominated “ hydra- 
tion ” at all in the sense of a summer condition. From an 
estimate based on several winters’ experience, a vaporisa- 
tion of water which supplied a half grain of vapour per 
cubic foot of air introduced, when an increment of four to 
six grains for the same volume of air would be requisite to 
get the summer condition of humidity corresponding to the 
internal temperature, has proved sufficient to give a sensibly 
pleasant air, while the absence of this supply was at once per- 
ceptible in the house. A low pressure hot-water apparatus, 
whose temperature never reached the boiling-point, and 
rarely exceeded i 8 o°, giving heat to a large volume of fresh 
air, which, at the mouths of supply to the rooms, was not 
much above go° at any time, was the source of heat. 
§. It is very difficult to find any hypothesis which will 
account for this requirement of a small supply of vapour 
with heated air when we admit, or can demonstrate, that 
the sufficient quantity to the senses is so far below what is 
needed for hydration, and so independent from the moisture 
condition of the air; for nearly the same small quantity of 
vaporisation seems desirable in air heated from any tempe- 
rature. The explanation of the offensiveness of heated air 
currents has been sought with much diligence, and, at 
times, causes have been assigned with much positiveness. 
One of the earliest of these explanations (but one which 
yet finds supporters) was found in the substitution of trans- 
ferred or converted heats by currents of air for the radiant 
heat of fire. Open fires were to be restored as the means of 
securing pleasant air . The healthfulness and comfort of our 
ancestors were to come back to their degenerate children. 
Gathered around a blazing fire, roasted on one side and 
frozen on the other ; restricted to one fire in the house, as 
all the others would smoke ; the chamber-heating apparatus 
reduced to the warming-pan ; victims of rheumatism, 
sciatica, tic-doloreux, and ague — the diseases of fifty years 
ago — the good old times were to come back. Alas ! there 
were obstinate innovators, and the world would not be con- 
vinced of the advantages of radiant heat as the sole means 
of warming. 
This point being established, at a later time, surfaces at 
high temperatures for imparting heat to the air of a room, 
either by ventilating currents or direCt heating, including 
all fire-heated surfaces, together with steam-heated ones, 
above the boiling-point, or 212 0 , were utterly condemned. 
