Transcription:
Address correspondence to Official In Charge Local Office, Weather Bureau U.S..DEPARTMENT OF AGRICULTURE LOCAL OFFICE
OF THE WEATHER BUREAU Merchants Exchange. Rooms 1500-6 SAN FRANCISCO, CAL. March 19, 1910. Mr. John Muir, Martinez,
Cal. Dear Mr. Muir:- I have not forgotten your request regardingthe number of water drops in a cloud; but I find it hard
to get down to definite statements. I'd much rather talk it. over with you, and yet that wouldn't do either, for we'd get
off on other matters of equal and everlasting interest. First, as you look up into the sky, remember that the seemingly limitless
ocean of air, at the bottom of which we waddle, is not much deeper than the distance from one great peak in the Sierra to
another. When you stood on Whitney you were up nearly four-tenths of the way, that is, nearly half of the so-called homogeneous
atmosphere is below one at a height of 5,500 meters (31/2 miles). At an elevation of six miles nearly, two-thirds of the atmosphere
is below us. At this elevation you are above what we may call the muddy or dirty part of the atmosphere. It is clean mud,
almost entirely water. Most people call it clouds; but it is none the less a sediment of water and fine dust. Below the level
named, the air is in a turbulent condition as a rule, convectional currents rising, falling and in fact swirling in every
direction. I sometimes 04734