1850."| 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 



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radiation from a scale of wood or metal. It should be suspended 

 at such a distance from all buildings and from the p-ound, as 

 should effectually guard it from interferences of this nature. It 

 will be a matter of surprise to those who have not had experience 

 in observations of this nature, to find how very few degrees a 

 thermometer thus situated will rise above one in the shade. 



lY.—The Rain-Gauge. 



This instrument measures the quantity of rain that falls in any 

 given spot. The principle of it is the following: — If we imagine 

 the surface of the ground over which a shower of rain has passed 

 to be perfectly horizontal and impervious to moisture, so that the 

 whole quantity of water should be retained, it would cover the 

 surface to a certain depth, which, measured in inches, would be the 

 depth of rain which had fallen. In calculating this depth by 

 means of the rain-gauge, we expose a small surface to the recep- 

 tion of the rain, and measure the depth of what it receives. A 

 shower may, however, pass by it, and, although much may fall at 

 no great distance, not a drop may reach the exact spot occupied by 

 the rain-gauge itself. Hence, to obtain the exact amount of rain 

 which falls in any given district, several rain-gauges should be 

 dispersed in various parts, and the mean of the whole amount 

 received would be the true quantity due to such locality. 



In this busy world of ours, however, observers (most of whom 

 have important business of their own) are generally satisfied with 

 registering the amount of rain received by their own gauges at 

 9 A.M. every day; and with the imperfect results deduced from these 

 registers we must be satisfied, until a more extensive love for 

 science is created and the number of observers multiplied. 



Rain-gauges are of various constructions. In some, a glass 

 tube, divided into inches, proceeds from the bottom of the vessel 

 in which the rain is received, and the amount having been read off, 

 the water is discharged by a stop-cock, in readiness for the next 

 day. In others, a float is elevated by the water, and the scale 

 which is attached to it shows the depth of rain received. 



Perhaps the most simple is the one which I have adopted, and 

 which is never liable to be out of order. A circular copper 

 funnel, 12 inches diameter, is connected by a pipe with a vessel 

 capable of holding a gallon, or more. To the bottom of this 

 vessel is attached a stop-cock, by means of which the rain is 

 drawn off and measured in a graduated glass cylindrical jar. 

 Now, if a represent the diameter of the receiving vessel, and 6 

 that of the jar, c the depth of rain in the vessel, and x the 

 required depth of the glass jar to measure such amount, then, 

 since area, multiplied by the depth, gives the volume — 



■7854 a-c = "7854 6-jr; or, a"c := b'x. 



Now, suppose the diameter of the glass jar to be 2 inches, and it 

 is required to find what the depth of the jar will measure |-inch, 

 we have — 



12' X "25 = ^'x; or, x = 9. 



Nine inches of the jar, 2 inches in diameter, will therefore mea- 

 sure one-quarter of an inch of rain, received by a surface 12 

 inches in diameter. One twenty-fifth part of nine inches will 

 consequently measure one-hundredth of an inch; and the thou- 

 sandths may be estimated. 



The rain-gauge should be only a few feet from the ground, and 

 in every case its height should be stated, as it is invariably found 

 that more rain is received near the surface than at a superior 

 elevation. Indeed, it should be agreed upon by observers that 

 their gauges should all be at the same height, and all equally free 

 from the interference of buildings or trees. Till some rule of this 

 kind is adopted, we are not in a position to compare accurately the 

 quantity of rain which falls in different districts. At Greenwich 

 there are several rain-gauges at different heights above the 

 ground. 



The following table will show the differences between the quan- 

 tity of rain received by them in 1846 and 1847: — 



Height abore Inches of rain Inches of rain 



tube, about 4-'"<^'i '" diameter, of a syphon-like form, one end 

 being again bent at riglit angles to the general direction of tlie 

 tube, so as to present a horizontal opening to the wind. The tube 

 is half-filled with water, and the pressure of the wind on that 

 portion directed towards it will drive the water up the other lej'. 

 A scale is attached, by which the force of the wind is ascertainetl ; 

 and the whole turns freely on a vertical axis, so that the mouth 

 may always be towards the quarter from whence the wind blows. 

 The following table shows the pressure per square foot for the 

 indications of the scale. 



Not having a convenient place to fix this instrument, for it 

 should be far above the interference of buildings or trees, I gene- 

 rally estimate the force of the wind from the knowledge gained 

 by its occasional use. Many observers do so without any reference 

 to the wind-gauge at all; and from following the directions in 

 the table subjoined, they cannot be far out. A calm is universally 

 represented by 0; a hurricane, or violent gale, by 6. 



Table. — Showing the Force of the Wind on a Square Foot for differ- 

 ent Heif/hts of the Column of Water in "Lind's Wind-Gauge." 



\.—The Wind-Gauge. 



The most simple instrument for ascertaining the force of the 

 wind, and the one most likely to be made use of by the generality 

 of observers, is that invented by Dr. Lind. It consists of a glass 



It now only remains for me to speak of the position of the 

 instruments which I have enumerated. 



The barometer may be placed in a sitting-room; for as the 

 correction for temperature is always applied, the degree of heat 

 will produce no difference in the results. It should be so situated 

 as regards light that it may be easily read off. To support the 

 wet and dry bulb and register thermometers, I use a stand of such 

 a height as to allow the bulbs to be about four feet from the ground ; 

 the top sides and back of this stand are covered with an external 

 case of wood-work, separated from the internal, which is of the 

 same materials, by a vacant space of two inches, by which means 

 a stratum of air, which is a bad conductor of heat, is always inter- 

 posed; and the heat of the sun which shines on the outer case is 

 prevented from reaching the inner compartment which contains 

 the thermometers; they face the north, and are placed so that they 

 cannot be affected by the radiation of heat from neighbouring 

 walls or buildings, and the sides of the stand project so as to 

 protect them from the sun when his azimuth is north of the east 

 or west. A series of holes, not however opposite to each other, 

 is bored in the inner and outer case, which admit the air, but not 

 the rays of the sun. Mr. Glaisher has shown, and his result may 

 be verified by experiment, that the indications both of the wet and 

 dry thermometers will be the same whether they are exposed to a 

 draught of air or protected from it. 



The following works must be procured by those who wish to 

 become observers: — Glaisher's 'Hygrometrical Tables,' which treat 

 of the wet and dry bulb thermometers, and the deductions from 

 observations made with them, price 2*. 6d. 



The 'Report of the Committee of Physics of the Royal Society ; ' 

 here may be found a good table for the temperature correction, li. 



Prices of the instruments enumerated: barometer, 71. 7s.; wet 

 and dry bulb thermometer, 2/. 2$; register thermometers, 2/. 2s. ; 

 rain gauge, 2/, 10«.; wind gauge, 11 is. Mr. Clark, 13, Moorgate- 

 street, will supply paper ruled in such a manner as to afford .i 

 convenient space for the record of all the observations. 



I have thus given a popular view of the construction and use of 

 the most available meteorological instruments, and shall be happy 

 if my introduction of the subject should lead to a large increase of' 

 the number of observers. About forty at present send in regular 

 reports to the Registrar-General; but let us hope that the present 

 movement, of which the formation of the British Meteorological 

 Society is the indication, may enlist ten times that number, and 

 that the labours of its members may tend to raise the study of 

 atmospheric phenomena to a position equal to that held by sciences 

 which have originated in our time. The observations require care, 

 perseverance, and a desire to promote the interests of science. 



