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Page:Popular Science Monthly Volume 41.djvu/250

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THE POPULAR SCIENCE MONTHLY.

DUST AND FRESH AIR.
By T. PRIDGIN TEALE, F. R. S.

EXCEPT in the case of museums, few serious attempts have been made to exclude dust from rooms, closets, cupboards, and drawers, to the contents of which, not infrequently, dust is simply ruinous. We allow dust to run riot among our things of value, and then go to considerable expense to render them clean again, only to start them on a fresh career of defilement.

Looked at in the abstract, is not our passive capitulation to dust incomprehensible? When I enter an office in a town and see the window-sills and papers dotted with soot, or go into a bed-room and see the toilet-table defaced with blacks, and know that the soot and the blacks need not be there, I can not refrain from asking how comes it to pass that we so patiently submit to such perpetual discomforts. You will doubtless reply, We agree with you as to the existence of the evil, but how is it to be remedied? My object is to offer some practical suggestions whereby you may so far mitigate and reduce the evils of soot and dust as to make them tolerable, perhaps even to lay down principles by which the evils can be annihilated in those instances in which the result to be obtained is worth the cost of achievement. For the practical purposes of every-day life it may turn out that we had better be content with approximate perfection, a condition of existence which compels us to be content with approximately pure water from a filter, and approximately pure air in our living-rooms.

If dust is to be kept out of any cavity, we must first find out why the dust gets in, in spite of good workmanship and accurate fitting. The reason is simple, ridiculously simple when stated, but, curiously, it has been little, if at all, thought of, and certainly hardly ever acted upon in practice. And the reason is this: Closets, cupboards, drawers, and boxes contain air; if the air were inelastic and never altered in volume, there would practically be no entrance of dust into these closed cavities. Unfortunately for our cleanliness, air is changing in volume incessantly. We are all familiar with the barometer, and most of us no doubt understand why the quicksilver rises and falls in the glass tube, or why, in the aneroid barometer, the index moves to right or left. Let us consider what these changes mean, and what they record.

When the air around us becomes condensed—shrinks into a smaller volume—it becomes heavier, puts greater pressure on the surface of the mercury, and makes it ascend in the tube; then the mercury is said to rise. When the air expands—swells into a larger volume—it becomes lighter, the pressure on the mercury