. A laboratory course in plant physiology. Plant physiology; Plant ecology. ELIMINATION 183 Belfort Observatory, Ealtimore, Md. The Draper forms are made at less cost by the Draper Manufacturing Company of New York City. All of these instruments are prone to work out of true and should be standardized often by comparison with standard thermometer, wet- and dry-bulb thermom- eters, and mercurial barometer respectively. Nor do they record with minute accuracy, though they are correct enough for most purposes. Photometers. No form of light recorder suitable for physiological uses yet exists, for
. A laboratory course in plant physiology. Plant physiology; Plant ecology. ELIMINATION 183 Belfort Observatory, Ealtimore, Md. The Draper forms are made at less cost by the Draper Manufacturing Company of New York City. All of these instruments are prone to work out of true and should be standardized often by comparison with standard thermometer, wet- and dry-bulb thermom- eters, and mercurial barometer respectively. Nor do they record with minute accuracy, though they are correct enough for most purposes. Photometers. No form of light recorder suitable for physiological uses yet exists, for the meteorological burning-glass type and black-bulb-ther- mometer types record only variations between sunlight and cloudiness. Clements has described a photometer, utilizing the darkening of photo- graphic paper ("Plant Physiology and Ecology," 73), but it is laborious of operation and does not yield a graph. Accordingly in my own laboratory I have made use of an empirical system as follows. The percentage of. Fig. 47.—The Richard barograph; Xk- From the Price-list of Richard Freres, Paris. light of full sun at noon in this latitude, in comparison with the full light of the sun overhead taken as 1, is determined for each day of the year; then a curve for each day is constructed by drawing a parabola through the hours of sunrise, noon, and sunset, and this is the curve of full sunlight. For cloudy days this curve is lowered after the following system, viz., for fleecy clouds or haze, to 90% of the full amount; for heavier clouds alternating with blue sky, 85%; for light continuous clouds, 80%; overcast dark clouds, 60%; heavy rain, 50%; heavy snow, 40%. The light record is thus drawn as a graph on the same horizontal scale as the records of thermograph, hygro- graph, and transpirograph. A fuller description of the details, together with an illustration of the use of these graphs, will be found in Miss Clapp's paper cited under Materials earlier (page 172). The subj
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