As it requires about ten years of careful observation to determine approximately the average or normal temperature of a locality, and perhaps twenty years to determine the normal rainfall, few farmers would feel that they had the time or skill to devote to so serious an undertaking ; nor is it necessary that they should. This work has been done already in the United States, and with great accuracy and care. The Weather Bureau of the United States Department of Agriculture has collected and tabulated all records of temperature and rainfall that have been made in the United States. Some of these records cover a period of more than a hundred years, many of them more than fifty years, and the work still is going on. At present, observations are being made at about 4000 places. With this number of records, distributed more or less evenly over the entire country, it is possible
WEATHER RECORDS to determine very accurately the normal temperature and rainfall for almost any locality in the United States.
A similar system is in operation by the Canadian Government, and information as to the climate of almost any inhabited locality in the Canadian provinces may be had on application to the Director of the Canadian Meteorological Service, Toronto.
The data are usually compiled by months. For example, the normal temperature and rainfall by months for Ithaca, N. Y., are as follows: Normal or average temperature, 31 years record: January, 24° ; February, 25° ; March, 32° ; April, 44° ; May, 57° ; June, 66° ; July, 71° ; August, 68° ; September, 61° ; October, 50° ; November, 38° ; December, 28° ; Annual, 47°. Normal or average precipitation in inches and hundredths of inches, including melted snow: January, 2.07 ; February, 1.84 ; March, 2.42 ; April, 2.30 ; May, 3.39 ; June, 3.73 ; July, 3.51 ; August, 3.06 ; September, 2.89 ; October, 2.96 ; November, 2.50 ; December, 2.30 ; Annual, 32.97.
These values would be considered approximately correct for a radius of twenty to fifty miles, depending principally on the topography, whether mountainous or level, and the proximity of large bodies of water and the prevailing wind direction. It is recognized that there may be an appreciable difference between the climate of a valley and that of an adjacent hill, or, on account of differences of soil character, between one farm and another in the same locality. Such local variations are usually small, although important, particularly in such matters as air drainage and frost, and can be determined only by observations made on the spot. The averages, compiled by the Weather Bureau, include observations made on hill-tops as well as in valleys, and, therefore, represent strictly average conditions. They have been carefully computed, and may be relied upon with confidence.
How climatic data may be secured.
The Climatological Service of the U. S. Weather Bureau is organized by sections, each section embracing a single state, except in the case of some of the smaller states, which are included in one section. The New England States make up one section ; also Delaware, Maryland, and the District of Columbia. The work of each section is under the supervision of a section director, in whose office are kept all records pertaining to his section. The accompanying list gives the city in which the office of each section director is located, and the section under his charge. A request for climatic data should show clearly (1) the locality for which the data are desired, and (2) the character of the data, and should be addressed, Section Director, Local Office, Weather Bureau, followed by the appropriate city and state: —
Probably the most important information for the general farmer concerning the climate of his locality is the average temperature and rainfall by months, but the following data are available for practically all parts of the United States, having been compiled in 1906 and published in Bulletin Q, to which reference should be made when making request : Temperature by months ; mean or average ; mean of maxima ; absolute maximum ; mean of minima ; absolute minimum ; highest monthly mean ; lowest monthly mean ; precipitation, including melted snow ; mean or average ; number of days with .01 inch (one hundredth of an inch) or more ; total amount for the driest year ; total amount for the wettest year; dates on which the extreme temperatures for the locality occurred. For northern states the dates are given generally when the minimum temperature fell to -10 (10 below zero) or below, and the maximum rose to 90° or above; for southern states, when the minimum fell to 32° or below, and the maximum rose to 95° or above.
Making local observations.
The value of climatic information, supplied by the Weather Bureau, may be enhanced greatly by observations of temperature and rainfall made on the farm, particularly if made in connection with phenological observations suggested on pages 17-19. Such a record is a valuable asset to a farm, and its value increases as each year's record is added. A suitable equipment need not be expensive, nor the work made laborious. The highest and lowest temperature may be obtained at a single reading, made preferably about sunset, by use of Six's pattern of maximum and minimum thermometers, mentioned on page 1. The average of the two thermometer readings gives the daily mean. This is the method used by the Weather Bureau, and will make the record strictly comparable with any data obtained from that source.
A serviceable rain-gauge may be constructed by the use of any vessel having straight sides. A tomato-can, placed two feet above ground, and fifty feet from buildings or trees, will give good results. The depth of the water caught may be measured with an ordinary rule, but to make the record comparable with those made by the Weather Bureau, the fractions of an inch should be reduced to decimals. Perhaps it would be better to make a rule graduated in inches and tenths. Ten inches of average snow will make, when melted, one inch of water.
A convenient method for recording and preserving weather observations is important. A book is preferable, having at least thirty-four ruled lines. Use one page for each month. Rule the page into eight columns, leaving ample margin on the right for phenological notes. Beginning at the left, head the columns as follows : date ; highest temperature ; lowest; mean; rainfall; snowfall; wind direction (every farm should have a good weather-vane); weather; phenology. Enter each day's record on line with appropriate date. Under phenology full notes should be made, showing the condition and advancement of the various crops, for here is the point of contact between current weather and plant growth. All this may be combined with a diary of farm work. At the end of each month the temperature columns should be averaged and the total rainfall set down; and when these values are compared with the normal, the importance of the climatic factor in crop production will be more fully understood. (For thermometer scales, see Chap. XXVII.)