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Read Ebook: A Treatise on Meteorological Instruments Explanatory of Their Scientific Principles Method of Construction and Practical Utility by Negretti Enrico Angelo Lodovico Zambra Joseph
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Ebook has 105 lines and 22402 words, and 3 pages
the solid ingredients being in excess for certain conditions of solution, depending upon temperature chiefly, and perhaps electricity and the action of light also, appear as crystals and disappear with the various changes that occur in the weather.
The various appearances thus presented in the menstruum have been inferred to prognosticate atmospheric changes. The following rules have been deduced from careful study of the glass and weather:--
"Before, and in a continued southerly wind, the mixture sinks slowly downward in the vial, till it becomes shapeless, like melting white sugar.
"Before, or during the continuance of a northerly wind , the crystallizations are beautiful ; but the least motion of the liquid disturbs them.
"Repeated trials with a delicate galvanometer, applied to measure electric tension in the air, have proved these facts, which are now found useful for aiding, with the barometer and thermometer, in forecasting weather.
"Temperature affects the mixture much, but not solely; as many comparisons of winter with summer changes of temperature have fully proved.
"A confused appearance of the mixture, with flaky spots, or stars, in motion, and less clearness of the liquid, indicates south-easterly wind, probably strong to a gale.
"The glass should be wiped clean now and then,--and once or twice a year the mixture should be disturbed, by inverting and gently shaking the glass vial."
Self-registering thermometers should be protected by a similar screen. It has been found that thermometric observations made at sea are not valuable for scientific purposes unless the instruments have been duly protected by such a screen.
In a small box, 8 in. by 8 in. by 4 in., a complete set of meteorological instruments have been packed. The lid of the box, by an ingenious arrangement, is made to take off and hang up; on it are permanently fixed for observation, a maximum and minimum, and a pair of dry and wet bulb thermometers. The interior of the box contains a maximum thermometer in vacuo for solar radiation, and a minimum for terrestrial purposes, one of Negretti and Zambra's small pocket aneroid barometers, pedometer for measuring distances, pocket compass, clinometer, and lastly a rain gauge. This latter instrument consists of an accurately turned brass ring having an india rubber body fastened to it to receive the rain, which is measured off by a small graduated glass, also contained in the box. Gentlemen travelling will find this compact observatory all that can be desired for meteorological observations.
A simple kind of hydrometer is very much used at sea, as "a sea-water test;" and as the observations are usually recorded in a meteorological register or the ship's log-book, it may not be altogether out of place to give a description of it here.
It is constructed of glass. If made of brass, the corrosive action of salt-water soon renders the instrument erroneous in its indications. The shapes usually given to the instruments are shown in figs. 96 and 97. A globular bulb is blown, and partly filled with mercury or small shot, to make the instrument float steadily in a vertical position. From the neck of the bulb the glass is expanded into an oval or a cylindrical shape, to give the instrument sufficient volume for flotation; finally, it is tapered off to a narrow upright stem which encloses an ivory scale, and is closed at the top. The divisions on the scale read downward, so as to measure the length of the stem which stands above the surface of any liquid in which the hydrometer is floated. The denser the fluid, the higher will the instrument rise; the rarer, the lower it will sink.
The indications depend upon the hydrostatic principle, that floating bodies displace a quantity of the fluid which sustains them equal to their own weight. According, therefore, as the specific gravities of fluids differ from each other, so will vary the quantities of the fluids displaced by the same body when floated successively in each.
A small tin, copper, or glass cylinder is useful for containing the water to be tested. It should be wider than the hydrometer, and always filled to the brim. If fitted to a stand, which is supported by gimbals, it will be very convenient. Water in a bucket, basin, or other wide vessel, acquires motion at sea, and the eye cannot be brought low enough to read off the scale accurately.
Errors of observation may occur with the hydrometer, if it be put into water without being clean, or without being carefully wiped. The instrument is extremely accurate if correctly used. It should be kept free from contact with the sides of the vessel; and all dust, smears, or greasiness, should be scrupulously avoided, by carefully wiping it with a clean cloth before and after use.
Whenever the temperature of the water tested differs from 62?, a correction to the reading is necessary, for the expansion or contraction of the glass, as well as the water itself, in order to reduce all observations to one generally adopted standard.
Negretti and Zambra's hydrometer, with thermometer in the stem, shows the density and temperature in one instrument.
For the following Tables we are indebted to the kindness of Admiral FitzRoy:--
TABLE for reducing observations made with a BRASS HYDROMETER, assuming the linear expansion of brass to be 0?000009555 for 1? F. The correction is additive for all temperatures above 62?, and subtractive for temperatures below 62?.
TABLE for reducing observations made with a GLASS HYDROMETER, assuming the linear expansion of glass to be 0?00000463 for 1? F. The correction is additive for temperatures above 62?, and subtractive for temperatures below 62?.
At places where the phenomena of the tides are of much maritime importance, a continuous series of observations upon the rise and fall, and times of change, is essentially necessary as a basis for the construction of good tide tables; and as such observations should also be accompanied with the registration of atmospheric phenomena, we have no hesitation in inserting a description of an accurate self-registering tide-gauge.
ADDENDA.
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.
OLD FRENCH LINEAL MEASURE.
The above methods of recording the force of wind and state of weather were originally proposed by Admiral Sir Francis Beaufort. They are now in general use at sea, and by many observers on land.
Platinum 0?0008842 of the length. Glass, Flint 0?0008117 " " with Lead 0?0008622 " Brass 0?0018708 " Mercury 0?0180180 " Water 0?0433200, from 39? to 212? Alcohol 0?1100 " 32? to 174? Nitric Acid 0?1100 Sulphuric Acid 0?0600
Water 1?000 Alcohol, pure 0?791 " proof 0?916 Mercury 13?596 Glass 3 to 2?7 Brass 7?8 to 8?54 Platinum 21 to 22?00
Weight of a cubic foot of water, at the temperature of comparison, 62?425 lbs. avoirdupois.
The pound avoirdupois contains 7,000 grains.
Air is 813?67 times lighter than water.
? Water boiling at 212 Mercury boils at 660 Sulphuric Acid " 590 Oil of Turpentine " 560 Nitric Acid " 242 Alcohol " 174 A Saturated Solution of Salt " 218 Vital Heat 96 Olive Oil begins to solidify 36 Fresh Water freezes 32 Sea Water freezes 28 Mercury freezes -39
These valuable data indicate the characteristics of the weather in each month in the suburbs of London, and will be found tolerably accurate as indications of weather, and serviceable as standards for comparisons of observed results, at most places in England.
STANDARD WORKS ON METEOROLOGY
SUPPLIED BY NEGRETTI & ZAMBRA.
LONDON: PRINTED BY STRAHAN AND WILLIAMS, 7 LAWRENCE LAND, CHEAPSIDE, E.C.
NEGRETTI & ZAMBRA'S
PATENT RECORDING AND DEEP-SEA THERMOMETER.
This Thermometer differs from all other Registering or Recording Thermometers in the following important particulars:--
DESCRIPTION OF THE DEEP-SEA RECORDING THERMOMETER.
In the first place, it must be observed that the bulb of the Thermometer is protected so as to resist the pressure of the ocean, which varies according to depth that of three thousand fathoms being something like three tons pressure on the square inch. The manner of protecting the bulb was invented by Messrs. Negretti and Zambra in 1857, and has been latterly copied by other persons and brought out as a new invention. The manner of protecting the bulb has been described by the late Admiral R. FitzRoy, in the first number of Meteorological Papers, page 55, published July 5th, 1857, as follows:
"Referring to the erroneous readings of all thermometers, consequent on their delicate bulbs being compressed by the great pressure of the ocean, he says:--'With a view to obviate this failing, Messrs. Negretti and Zambra undertook to make a case for the weak bulbs, which should transmit temperature, but resist pressure. Accordingly a tube of thick glass is sealed outside the delicate bulb, between which and the casing is a space all round, which is nearly filled with mercury. The small space not so filled is a vacuum, into which the mercury can be expanded, or forced by heat or mechanical compression, without doing injury to or even compressing the inner or much more delicate bulb.'"
The construction of this instrument for deep-sea temperatures is as follows:--
The contrivance for turning the Thermometer over may be described as a frame with a vertical propeller; to this frame the instrument is pivoted. On its descent through the water the propeller is lifted out of gear and revolves freely on its axis; but so soon as the instrument is pulled towards the surface the propeller falls into gear and revolves in the contrary direction, turning the Thermometer over once, and then becoming locked and immovable.
Negretti & Zambra's Patent Atmospheric Recording Thermometer, Fig. 3, differs from the Deep-sea Thermometer by its not having the double or protected bulb, it not being required for resisting pressures. In this case the instrument is turned over by a simple clock movement, which can be set to any hour it may be desirable; the Thermometer is fixed on the clock, and when the hand arrives at the hour determined upon, and to which the clock is set as in setting an alarum clock, a spring is released and the Thermometer turns over as before described.
Messrs. Negretti and Zambra have arranged a Wet and Dry Bulb Hygrometer upon the same plan.
NEGRETTI & ZAMBRA'S PRICE LIST OF STANDARD METEOROLOGICAL AND OTHER PHILOSOPHICAL INSTRUMENTS.
? s. d.
Ditto ditto with Millemetre and English scales 9 9 0
Ditto ditto with tube, 0?45 internal diameter and millimetre scale 10 10 0
Ditto ditto arranged for observations being taken by the Cathetometer 18 18 0
Ditto ditto Fig. 8 ?3 3 0 3 10 0
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