Page:Popular Science Monthly Volume 36.djvu/325

Rh forces tending to concentrate the more important branches of the cotton manufacture along the south shore of New England. I hesitate to treat the subject of the influence of relative and absolute humidity upon cotton spinning and weaving, because none of us have yet any very accurate or scientific knowledge upon the subject; but, in order that a beginning might be made and the basis of an investigation might be laid down, I wrote to General A. W. Greely, giving the terms of the problem in a general way, and he has very kindly and carefully prepared tables for me which it might be judicious to incorporate in this report, giving the mean relative humidity three times a day—at 7, at 3 , and at 11 as well as the temperature. These observations are averaged separately for each month in the year, and in the accompanying tables the mean for five years, 1881 to 1885, is charted. My hypothesis had been that somewhere between the elbow of Cape Cod and Staten Island the cotton manufacture of the United States would gradually concentrate. That hypothesis, so far as relative humidity may be a factor in the case, is fully sustained by these tables. From General Greely's figures I have taken the mean temperatures at the same hours of the day and the mean relative humidity in New London, Conn., and Augusta, Ga. The conditions are shown by curves on these charts.

As is quite well known, the term "relative humidity" defines the ratio of the moisture in the air to the amount which would saturate the air at a given degree of heat. Saturation being called one hundred, this factor is represented on the chart by percentage. The absolute humidity, or absolute number of grains of moisture contained in each cubic foot of air, will of course vary with the temperature of the atmosphere, and the absolute humidity at the South may be greater than that of the North, owing to the higher degree of heat.

I think all will agree with me that spinning and weaving depend more upon the uniform conditions of relative humidity in respect to spinning, perhaps more on absolute humidity in respect to weaving, than upon almost any other climatic condition. General Greely remarks: "In locations distant from the coast there is a greater diurnal range of relative humidity in the atmosphere, owing to the heating effect of the sun's rays upon the atmosphere, causing the temperature of the air to increase more rapidly than the dew-point, thus making the air relatively dry during the working hours of the day. It is possible that this condition has tended to drive the cotton-mills toward the southern coast of New England, where they are more completely covered by the vapor laden winds from neighboring waters, causing a reduced diurnal range in temperature and a more constant relative humidity."