expansion made, the number of drops counted, and the calculation made as before. The table on page 36 gives the results of some tests made with this apparatus.
"These numbers are, of course, very variable, owing to changing conditions, but the figures obtained with the newer forms of apparatus do not differ greatly from these. Although we were prepared to find that, if the number of dust-motes in a sunbeam should ever be counted, the number would be very great, yet I imagine to most of us the above figures are almost a revelation, as the visible dust-motes do not amount to more than a small fraction of these numbers. The figures show that some of the dust particles must be inconceivably small, almost molecular in their dimensions. Millions in a cubic centimeter, and yet so light that their united mass cannot be weighed, and almost none of them visible with the highest powers of the microscope, and yet, for the reasons already given, these very small particles of matter are not gaseous."
BEBBER W. J. VAN, "Hygienische Meteorologie," Stuttgart, 1895.
Memoirs by HENRY DE VARIGNY, F. A. R. RUSSELL, and J. B. COHEN, in Annual Report of the Smithsonian Institution, 1895, pp. 135-386.
AITKEN J., Papers in Transactions Royal Society of Edinburgh, vols. xxxv, xxxvii, xxxix, and Proceedings Royal Society of Edinburgh, vols. xvi, xvii, xx.
"Report of the International Meteorological Congress, held at Chicago, Ill., August 21-24, 1894," published as Weather Bureau Bulletin No. 11, Washington, 1894, 1895, 1896.
BARUS CARL, "Report on the Condensation of Atmospheric Moisture," Weather Bureau, Bulletin No. 12, Washington, 1895.