Rain gauge

“ The specific locality sometimes requires its own rain measurements. A rain gauge of the Weather Bureau pattern is useful, but a metal container with straight sides will answer fairly well, and an inch rule will answer the purpose of a measuring stick. The volunteer observer who studies the rainfall of a locality may thus gain the essential information required; namely, the minimum amount of rain, and also the optimum rainfall both as to amount and distribution, for a specific crop. ”

“ Symons has devised another rain gauge of so ingenious and interesting a character that it needs only to become generally known among amateur meteorologists to be in universal demand. By its means an observer at a distant window may read off the rain as it falls. It is shown at Fig. 50, where the usual 5-inch funnel surmounts a long glass tube attached to a black board bearing a very open scale marking tenths of an inch in white lines; a white float inside the tube constitutes the index, which rises as the rain increases in quantity. ”

“ The rain gauge in the garden is a receptacle provided with a funnel through which the water runs, and the depth to which the earth would be covered if it were flat and there were no means of escape for the water, is recorded by a lever, which moves a pencil, the pointed end of which touches a piece of cardboard. Even lightning is made to record itself. A little stream of water for ever running through a pipe projecting from the wall of the observatory picks up any electricity in the air, and carries it into an instrument, which automatically notifies its presence. ”

“ A rain gauge is an apparatus for measuring the amount of the rainfall at any locality, and a wind gauge indicates the pressure and force of the wind. The boilers of steam engines are provided with a water gauge and a steam or pressure gauge. The purpose of the former is to enable the attendant to see whether or not there is a sufficient quantity of water in the boiler. ”

“ Rain-Gauge.—While measurements of rainfall can possess no climatological value unless they are carried on continuously at a fixed station, some very interesting observations may be made by the traveller both during the night when in camp, and during heavy showers when compelled to stop on the march. The rain-gauge is in itself the most simple of all scientific instruments, for it consists essentially of a copper funnel to collect the rain as it falls, and a bottle to contain what has been collected. A graduated measuring glass is the only accessory required. ”

“ Such examples show the importance of placing any rain-gauge, so far as possible, upon a plane surface of the earth—horizontal, or so inclined that, if produced, especially in the direction of prevailing winds, it will cut the mean levels of the area whose mean rainfall is intended to be represented by that gauge. It has been commonly stated that rainfall increases with the altitude. This is broadly true. A rain-cloud raised vertically upwards expands, cools and tends to precipitate ”

“ A pit and ring of concrete with a movable cover of wire mesh, coarse enough to permit rain to enter without obstruction and fine enough to keep leaves out makes an ideal position for a rain gauge in an open and fairly level country. ”

“ Not for over a century was the first thoroughgoing attempt made at systematic observation. There was a meteorological section in the Academy of Sciences at Mannheim from 1763, and subsequently a separate society for meteorology. In 1783, the Academy published observations from 39 stations, those from the central station comprising data from the hygrometer, wind vane (but not anemometer) , rain gauge, evaporimeter, and apparatus for geomagnetism and atmospheric electricity, as well as data from the thermometer and barometer. ”

“ The value of similar estimates of the rainfall by numerous observers would be very great to meteorology.
116. The principle of measurement in all these gauges is the relation existing between the areas of the collecting and receiving surfaces; that is, between the area of the funnel into which the rain falls, and the area of the cylinder which receives it. In Howard’s and Glaisher’s gauges, this cylinder is virtually the measuring glass itself; in the others, above described, the measuring scales show the same depth of water as in the cylinder of the gauge. ”

“ The minimum requirement of instrumental observations by a traveller is the reading twice daily of the barometer and of the dry and wet bulb thermometers, to ascertain the temperature and humidity of the air, also the reading once daily, in the morning, of the minimum thermometer which has been exposed all night, and on days in camp of the maximum thermometer also. It is very desirable to expose a rain gauge whenever it is practicable to do so. ”

“ When two equal drops of rain fall into a current of air at points where the velocity is not the same, one drop will either approach toward or recede from the other, and the quantity of rain falling on the space beneath will be increased or diminished. The large rainfall registered at the Signal-Service station on Mount Washington has recently been specially investigated. Four extra gauges, three inches in diameter, were set up seventy-five feet respectively north, east, south, and west from the station-gauge. ”

“ To observe and duly record the times of commencement and termination of rain is very desirable. Scarcely any observer can attempt to do this even approximately from personal observation. Hence the want of a cheap and simple self-recording rain-gauge is much felt, the present construction being too expensive for all but a few individuals.
In 1862, Mr. R. Strachan estimated the duration and amount of rain in London (Gray’s Inn Road) as follows:—
“During the year 1862, the rainfall amounted to 25·67 inches. ”

“ It is the belief of European meteorologists that the mean rainfall on the western portions of that continent varies little, if at all, when periods of many years are considered. In England there are rainfall records reaching back to 1677. Since 1725 these records are unbroken; at present there are more than 1,500 rain-gauge stations in that country. The Scotch observations extend to 1731, the Irish to 1791. ”

“ It is rare, however, to find rain so heavy as to give any appreciable depth when collected in a vessel freely open to evaporation, and in order to estimate the amount of rainfall to small fractions of an inch, the device is employed of measuring the water collected in the receiver of the gauge in a glass jar of much smaller diameter than the mouth of the collecting funnel. ”

“ The observations since 1883 have all been made by the 8-inch gauge and in the same position as that adopted by Dr. Chaplin.
Table I shows the fall of rain in every month during the 32 years ending with 1892.
In looking over the table the first thing noticeable is the very great difference in every month of the rainy season, between the falls in the same month in different years; for instance, in January the fall in the year 1873 was 0·13 inch, whilst in 1878 it was 13·39 inches. ”

“ The greater part of the decrease is due to wind. The stronger the wind, the greater the decrease with elevation. The less the diameter of the elevated gauge, the less will it indicate. A gauge on the leeward side of a tower may collect as much rain as one on the ground. ”

“ Some people are disposed to laugh at the forecasts made, but in the main they are very trustworthy.
Rain gauges and solar thermometers, Kew.
It is never possible to be quite sure what will happen at any one spot, but over a district the readings of the barometer afford the practised meteorologist a fairly accurate idea of what is coming, and it is worthy of note that the failures, or partial failures, in the prophecies during a year are considerably less than 20 per cent. On the coast the prognostications of the Meteorological Office have been of immense service. ”

“ In suburban localities and in communities where buildings are 100 feet apart the gauges are better placed in such positions as have the full sweep of the rain-bearing winds. If two places 100 feet or more apart show no material difference in the catch, either location is probably suitable. With gentle rain and still air the two gauges should be in close agreement; if the wind blows in strong gusts there may be a material difference. ”

“ The wind is the chief obstacle to accuracy of rainfall measurement and shielding the gauge from the full strength of the wind is the best means to insure an accurate catch. The Nipher shield is a trumpet-shaped metal device about 20 inches across which surrounds the mouth of the gauge. ”

“ This pressure varies according to the state of the weather, and the changes are indicated by an instrument called a barometer. Generally speaking, the falling of the mercury in the tube of the barometer indicates rain, and its rise heralds clear weather. Sometimes the rise is followed by cold winds, frost and ice. What these changes really indicate, however, can be determined only by comparing the barometric changes, at certain hours, in a number of places very far apart. This is done by the Signal Service. ”

“ A man who possesses a barometer and a thermometer, and knows how to read them, can beat all prophets out of the field. Change of weather is gradual, and great storms or changes are usually shown by falls of the barometer exceeding an inch, and by differences of temperature exceeding fifteen degrees. The more rapidly such changes occur, the more risk is there of severe weather. The normal height of the barometer in these latitudes is 29.24 to 30.00, though 27.45 has been registered in the Orkneys. A tenth of an inch an hour is a fall indicating a storm or very heavy rain. ”

“ In moderately level regions of gentle drainage the measurement of the precipitation derived from snow requires the care and judgment that comes only with experience. In mountainous regions it requires judgment, patience and a lot of hard work.
On the prairies of Indiana, for instance, the measurements made at the Weather Bureau stations give a pretty accurate total of precipitation. If the aggregate error amounted to 12 inches of snow, or even 2 inches of rain, however, the result would not be materially harmful. ”

“ It is a well-known fact that the barometer is as much, or even more affected by a change of wind as it is by rain; and the objection raised against a simple barometer reading, as leaving the observer in doubt whether to expect wind or rain, is removed by the addition of the Hygrometer, an instrument indicating the comparative degree of dryness or dampness of the air;—a most important item in the determination of the coming weather. ”

“ In general it is now conceded by several high authorities that the measured rainfall must be corrected for the influence of the wind at the gauge, if the latter is not annulled by Nipher’s or Boernstein’s methods. A practicable method of measuring and allowing for the influence of the wind, without introducing any very hazardous hypothesis, was explained by Abbe in 1888 (see Symons’s Meteorological Magazine for 1889, or the U.S Monthly Weather Review for 1899) . This method consists simply in establishing near each other several similar gauges at different heights above the ground. ”

“ He accounts for the production of clouds, the rise and fall of the Barometer by this cause, inferring, that at a certain height the rising air overflows the rest of the atmosphere, forming a ring of cloud vapor and air, which pressing on that below, occasions the rise of the barometer found at the edges of severe storms.
Mr. Thomas Hopkins of Manchester, in a work published in 1844, entitled “On the atmospheric changes which produce Rain, Wind and Storms,” admits with Mr. Espy the ascent and condensation of vapor in the air from various causes, and that all horizontal winds are thus produced. ”

“ The faster the precipitation, the sharper are the curves.
The Marvin gauge possesses several distinct advantages. Recording begins within a very few minutes after precipitation has commenced—a merit not possessed by tipping-bucket gauges; it likewise records the cessation of rainfall rather more promptly. A very desirable feature is the fact that it also records the rate of rainfall, a matter of great importance. In many instances the total of precipitation is of minor consequence, while the rate per unit of time must determine the discharging capacity of sewers and other run-off systems. ”

“ Now, as the vapor is so much lighter than the air, their mixture must also be lighter. So any unusual amount of moisture is at once detected by the barometer, an instrument for measuring the pressure of the atmosphere. If the air grow moister, and therefore lighter, the barometer falls; a storm is approaching.
Since cold air can retain but little moisture, if a warm moist current be chilled, it must lose a part of its vapor, which at once falls to the earth as rain. If the cold be somewhat greater, the moisture is crystallized into snow. ”

“ It is often desirable that observers should have two gauges, and that one of them should be capable of holding eight inches of rain. One of the gauges should be registered daily, the other weekly or monthly, as preferred, but always on the 1st of each month. ”

“ Even in this country, and near the sea-level, storms are frequent with the barometer not below [Pg 11] 29; rain is not uncommon with the glass at 30; even fine weather sometimes occurs with a low pressure; while it is evident that at an elevation of a few thousand feet the mercury would never rise to 30 inches; hence, according to the scale, there should never be fair weather there. If tempests happened as seldom in our latitude as the barometer gets down to 28 inches, the maritime portion of the community at least would be happy indeed. ”