The national utilisation of Meteorology in forewarning of storms, and the increasing employment of instruments as weather indicators, render a knowledge of their construction, principles, and practical uses necessary to every well-informed person. Impressed with the idea that we shall be supplying an existing want, and aiding materially the cause of Meteorological Science, in giving a plain description of the various instruments now in use, we have endeavoured, in the present volume, to condense

In the pursuits and investigations of the science of Meteorology, which is essentially a science of observation and experiment, instruments are required for ascertaining, 1. the pressure of the atmosphere at any time or place; 2. the temperature of the air; 3. the absorption and radiation of the sun’s heat by the earth’s surface; 4. the humidity of the air; 5. the amount and duration of rainfall; 6. the direction, the horizontal pressure, and the velocity of winds; 7. the electric condition of t

INSTRUMENTS FOR ASCERTAINING THE ATMOSPHERIC PRESSURE. 1. Principle of the Barometer. —The first instrument which gave the exact measure of the pressure of the atmosphere was invented by Torricelli, in 1643. It is constructed as follows:—A glass tube, CD (fig. 1), about 34 inches long, and from two to four-tenths of an inch in diameter of bore, having one end closed, is filled with mercury. In a cup, B, a quantity of mercury is also poured. Then, placing a finger securely over the open end, C, i

SYPHON TUBE BAROMETERS. 30. Principle of. —If some mercury, or any other fluid, be poured into a tube of glass, bent in the form of ∪ , and open at both ends, it will rise to the same height in both limbs, the tube being held vertically. If mercury be poured in first, and then water upon it at one end, these liquids will not come to the same level; the water will stand much higher than the mercury. If the height of the mercury, above the line of meeting of the fluids, be one inch, that of the wa

BAROGRAPHS, OR SELF-REGISTERING BAROMETERS. 33. Milne’s Self-Registering Barometer. —For a long time a good and accurate self-recording barometer was much desired. This want is now satisfactorily supplied, not by one, but by several descriptions of apparatus. The one first to be described was the design of Admiral Sir A. Milne, who himself constructed, in 1857, we believe, the original instrument, which he used with much success. Since that time several of these instruments have been made, and h

MOUNTAIN BAROMETERS. 37. The Syphon Tube Mountain Barometer, on Gay Lussac’s principle , constructed as described at page 31 , and fixed in a metallic tubular frame, forms a simple and light travelling instrument. The graduations are made upon the frame, and it is suspended for reading by a ring at the top, from beneath an iron tripod stand, which is usually supplied with it. Considerable care is requisite in adjusting the verniers, so as to keep the instrument steady and vertical. A drawback to

SECONDARY BAROMETERS. 43. Desirability of Magnifying the Barometer Range. —The limits within which the ordinary barometric column oscillates, do not exceed four inches for extreme range, while the ordinary range is confined to about two inches; hence it has often been felt that the public utility of the instrument would be greatly enhanced if by any means the scale indications could be increased in length. This object was sought to be obtained by bending the upper part of the tube from the verti

INSTRUMENTS FOR ASCERTAINING TEMPERATURE. 53. Temperature is the energy with which heat affects our sensation of feeling. Bodies are said to possess the same temperature, when the amounts of heat which they respectively contain act outwardly with the same intensity of transfer or absorption, producing in the one case the sensation of warmth, in the other that of coldness. Instruments used for the determination and estimation of temperatures are called Thermometers . Experience proves that the sa

SELF-REGISTERING THERMOMETERS. 69. Importance of Self-Registering Thermometers. —Heat being apparently the most effective agent in producing meteorological phenomena, the determination of the highest temperature of the day, and the lowest during the night, is a prime essential to enable an estimate of the climate of any place to be formed. To observe these extremes by means of the ordinary thermometer would be impracticable, from the constant watchfulness which would be necessary. Hence, the uti

RADIATION THERMOMETERS. 82. Solar and Terrestrial Radiation considered. —The surface of the earth absorbs the heat of the sun during the day, and radiates heat into space during the night. The envelope of gases and vapour, which we call the atmosphere, exerts highly important functions upon these processes. Thanks to the researches of Professor Tyndall, we are now enabled to understand these functions much more clearly than heretofore. His elaborate, patient, and remarkably sagacious series of e

DEEP-SEA THERMOMETERS. 89. On Sixe’s Principle. —Thermometers for ascertaining the temperature of the sea at various depths are constructed to register either the maximum or minimum temperature, or both. The principle of each instrument is that of Sixe. There are very few parts of the ocean in which the temperature below is greater than at the surface, except in the Polar Seas, where it is generally found to be a few degrees warmer at considerable depths than at the surface. When the instrument

BOILING-POINT THERMOMETERS. 91. Ebullition. —The temperature at which a fluid boils is called the boiling-point of that particular fluid. It is different for different liquids; and, moreover, in the same liquid it varies with certain changes of circumstance. Thus the same liquid in various states of purity would have its boiling temperature altered in a slight degree. There is also an intimate connection with the pressure under which a fluid is boiled, and its temperature of ebullition. Liquids

INSTRUMENTS FOR ASCERTAINING THE HUMIDITY OF THE AIR. 97. Hygrometric Substances. —The instruments devised for the purpose of ascertaining the humidity of the atmosphere are termed hygrometers . The earliest invented hygrometers were constructed of substances readily acted upon by the vapour in the air, such as hair, grass, seaweed, catgut, &c., which all absorb moisture, and thereby increase in length, and when deprived of it by drying they contract. Toy-like hygrometers, upon the princ

INSTRUMENTS USED FOR MEASURING THE RAINFALL. The instruments in use for measuring the quantity of rain which falls on a given spot are of very simple construction. Perhaps the simplest is:— 110. Howard’s Rain-Gauge. —It consists of a copper funnel, a stout glass or stone bottle, and a measuring glass. The bottle is to be placed upon the ground, with the funnel resting on its neck. A brass band or cylinder fixed upon the outer surface of the funnel envelops the neck of the bottle, and the pipe of

APPARATUS EMPLOYED FOR REGISTERING THE DIRECTION, PRESSURE, AND VELOCITY OF THE WIND. 122. The Vane. —The instrument by which the wind’s direction is most generally noted, is the vane, or weather-cock, and all that need be said of it here is that the points north, east, south and west, usually attached to it, should indicate the true and not the magnetic directions; and that care should be taken to prevent its setting fast. Very complicated instruments are required for ascertaining the pressure

INSTRUMENTS FOR INVESTIGATING ATMOSPHERIC ELECTRICITY. 131. Atmospheric Electroscope. —The simplest instrument for ascertaining at any time the electric condition of the atmosphere is an electroscope composed of two equal pieces of gold leaf, suspended from a brass support, and insulated, as well as protected from the movement of the air, by a glass covering. Fig. 90 represents such an instrument. The cap of the brass support is fitted for the reception, in the vertical direction, of a metallic

OZONE AND ITS INDICATORS. 139. Nature of Ozone. —During the action of a powerful electric machine, and in the decomposition of water by the voltaic battery, a peculiar odour is perceptible, which is considered to arise from the generation of a substance to which the term ozone has been given, on account of its having been first detected by smell, which, for a long time after its discovery, was its only known characteristic. A similar odour is evolved by the influence of phosphorus on moist air,

INSTRUMENTS NOT DESCRIBED IN THE PRECEDING CHAPTERS. 145. Chemical Weather Glass. —This curious instrument appears to have been invented more than a hundred years ago, but the original maker is not known. It is simply a glass vial about ten inches long and three quarters of an inch in diameter, which is nearly filled, and hermetically sealed, with the following mixture:—Two drachms of camphor, half a drachm of nitrate of potassium, half a drachm of chlorate of ammonium, dissolved in about two fl

1. French barometers are graduated to millimetres. An English inch is equal to 25·39954 millimetres. Hence, 30 inches on the English barometer scales correspond to 762 millimetres on the French barometer scales. Conversions from one scale to another can be effected by the following formulæ:— Of course, a table of equivalent values should be drawn up and employed, when a large number of observations are to be converted from one scale to the other. 2. In Germany, barometers are sometimes graduated