[From Household Words.]
GREENWICH WEATHER-WISDOM.
In England every body notices the weather, and talks about the weather, and suffers by the weather, yet very few of us know any thing about it. The changes of our climate have given us a constant and an insatiable national disease—consumption; the density of our winter fog has gained an European celebrity; while the general haziness of our atmosphere induces an Italian or an American to doubt whether we are ever indulged with a real blue sky. "Good day" has become the national salutation; umbrellas, water-proof clothes, and cough mixtures are almost necessities of English life; yet, despite these daily and hourly proofs of the importance of the weather to each and all of us, it is only within the last ten years that any effectual steps have been taken in England to watch the weather and the proximate elements which regulate its course and variations.
Yet, in those ten years positive wonders have been done, and good hope established that a continuance of patient inquiry will be rewarded by still further discoveries. To take a single result, it may be mentioned, that a careful study of the thermometer has shown that a descent of the temperature of London from forty-five to thirty-two degrees, generally kills about 300 persons. They may not all die in the very week when the loss of warmth takes place, but the number of deaths is found to increase to that extent over the previous average within a short period after the change. The fall of temperature, in truth, kills them as certainly as a well-aimed cannon-shot. Our changing climate, or deficient food and shelter, has prepared them for the final stroke, but they actually die at last of the weather.
Before 1838, several European states, less apt than ourselves to talk about the weather, had taken it up as a study, and had made various contributions to the general knowledge of the subject; but in that year England began to act. The officials who now and then emerge from the Admiralty under the title of the "Board of Visitors," to see what is in progress at the Greenwich Observatory, were reminded by Mr. Airy, the astronomer royal, that much good might be done by pursuing a course of magnetic and meteorological observations. The officials "listened and believed."
The following year saw a wooden fence pushed out behind the Observatory walls, in the direction of Blackheath, and soon afterward a few low-roofed, unpainted, wooden buildings were dotted over the inclosure. These structures are small enough and humble enough to outward view, yet they contain some most beautifully-constructed instruments, and have been the scene of a series of observations and discoveries of the greatest interest and value. The stray holiday visitor to Greenwich Park, who feels tempted to look over the wooden paling, sees only a series of deal sheds, upon a rough grass-plat; a mast some eighty feet high, steadied by ropes, and having a lantern at the top, and a windlass below; and if he looks closer, he perceives a small inner inclosure, surrounded by a dwarf fence; an upright stand, with a movable top, sheltering a collection of thermometers; and here and there a pile of planks and unused partitioning, that helps to give the place an appearance of temporary expediency, an aspect something between a collection of emigrants' cottages and the yard of a dealer in second-hand building materials. But—as was said when speaking of the Astronomical Observatory—Greenwich is a practical place, and not one prepared for show. Science, like virtue, does not require a palace for a dwelling-place. In this collection of deal houses, during the last ten years, Nature has been constantly watched, and interrogated with the zeal and patience which alone can glean a knowledge of her secrets. And the results of those watches, kept at all hours, and in all weathers, are curious in the extreme; but before we ask what they are, let us cross the barrier, and see with what tools the weather-students work.
The main building is built in the form of a cross, with its chief front to the magnetic north. It is formed of wood, all iron and other metals being carefully excluded; for its purpose is to contain three large magnets, which have to be isolated from all influence likely to interfere with their truthful action. In three arms of the cross these magnets are suspended by bands of unwrought, untwisted silk. In the fourth arm is a sort of double window, filled with apparatus for receiving the electricity collected at the top of the mast which stands close by. Thus, in this wooden shed, we find one portion devoted to; electricity—to the detection and registry of the stray lightning of the atmosphere—and the other three to a set of instruments that feel the influence and register the variations of the magnetic changes in the conditions of the air. "True as the needle to the pole," is the burden of an old song, which now shows how little our forefathers knew about this same needle, which, in truth, has a much steadier character than it deserves. Let all who still have faith in the legend go to the magnet-house, and when they have seen the vagaries there displayed, they will have but a poor idea of Mr. Charles Dibdin's sea-heroes, whose constancy is declared to have been as true as their compasses were to the north.
Upon entering the magnet-house, the first object that attracts attention are the jars to which the electricity is brought down. The fluid is collected, as just stated, by a conductor running from the top of the mast outside. In order that not the slightest portion may be lost in its progress down, a lamp is kept constantly burning near the top of the pole, the light of which keeps warm and dry a body of glass that cuts off all communication between the conductor and the machinery which supports it. Another light, for the purpose of collecting the electricity by its flame, is placed above the top of the pole. This light, burning at night, has given rise to many a strange supposition in the neighborhood. It is too high up to be serviceable as a lantern to those below. Besides, who walks in Greenwich Park after the gates are closed? It can light only the birds or the deer. "Then, surely," says another popular legend, "it is to guide the ships on the river, when on their way up at night; a sort of landmark to tell where-abouts the Observatory is when the moon and stars are clouded, and refuse to show where their watchers are."
All these speculations are idle, for the lights burn when the sun is shining, as well as at night; and the object of the lower one is that no trace of moisture, and no approach of cold, shall give the electricity a chance of slipping down the mast, or the ropes, to the earth, but shall leave it no way of escape from the wise men below, who want it, and will have it, whether it likes or no, in their jars, that they may measure its quantity and its quality, and write both down in their journals. It is thus that electricity comes down the wires into those jars on our right as we enter. If very slight, its presence there is indicated by tiny morsels of pendent gold-leaf; if stronger, the divergence of two straws show it; if stronger still, the third jar holds its greater force, while neighboring instruments measure the length of the electric sparks, or mark the amount of the electric force. At the desk, close by, sits the observer, who jots down the successive indications. In his book he registers from day to day, throughout the year, how much electricity has been in the air, and what was its character, even to such particulars as to whether its sparks were blue, violet, or purple in color. At times, however, he has to exercise great care, and it is not always that he even then escapes receiving severe shocks.
Passing on, we approach the magnets. They are three in number; of large size, and differently suspended, to show the various ways in which such bodies are acted upon. All hang by bands of unwrought silk. If the silk were twisted, it would twist the magnets, and the accuracy of their position would be disturbed. Magnets, like telescopes, must be true in their adjustment to the hundredth part of a hair's breadth. One magnet hangs north and south; another east and west; and a third, like a scale-beam, is balanced on knife-edges and agate planes, so beautifully, that when once adjusted and inclosed in its case, it is opened only once a year, lest one grain of dust, or one small spider, should destroy its truth; for spiders are as troublesome to the weather-student as to the astronomer. These insects like the perfect quiet that reigns about the instruments of the philosopher, and with heroic perseverance persist in spinning their fine threads among his machines. Indeed, spiders occasionally betray the magnetic observer into very odd behavior At times he may be seen bowing in the sunshine, like a Persian fire-worshiper; now stooping in this direction, now dodging in that, but always gazing through the sun's rays up toward that luminary. He seems demented, staring at nothing. At last he lifts his hand; he snatches apparently at vacancy to pull nothing down In truth his eye had at last caught the gleam of light reflected from an almost invisible spider line running from the electrical wire to the neighboring planks. The spider who had ventured on the charged wire paid the penalty of such daring with his life long ago, but he had left his web behind him, and that beautifully minute thread has been carrying off to the earth a portion of the electric fluid, before it had been received, and tested, and registered by the mechanism below. Such facts show the exceeding delicacy of the observations.