29,) is let down into the mine, where the air is warmer than the outside
air. Immediately the colder air outside presses down into the mine,
through the passage which is highest, being admitted by the escape of
an equal quantity of the warmer air, which rises through the lower
passage of the shaft, this being the first available opening for it
to rise through. A current is thus created, which continues as long
as the inside air is warmer than that without the mine, and no longer.
Sometimes a fire is kindled in the mine, in order to continue or
increase the warmth, and consequent upward current of its air.

This illustrates one of the cases where a "wise woman that buildeth
her house" is greatly needed. For, owing to the ignorance of architects,
house-builders, and men in general, they have been building
school-houses, dwelling-houses, churches, and colleges, with the most
absurd and senseless contrivances for ventilation, and all from not
applying this simple principle of science. On this point, Prof. Brewer,
of the Scientific School of Yale College, writes thus:

"I have been in public buildings, (I have one in mind now, filled with
dormitories,) which cost half a million, where they attempted to
ventilate every room by a flue, long and narrow, built into partition
walls, and extending up into the capacious garret of the fifth story.
Every room in the building had one such flue, with an opening into it
at the floor and at the ceiling. It is needless to say that the whole
concern was entirely useless. Had these flues been of proper
proportions, and properly divided, the desired ventilation would have
been secured."

And this piece of ignorant folly was perpetrated in the midst of learned
professors, teaching the laws of fluids and the laws of health.