A comet is a small body orbiting the sun on an elliptical path with a long tail of dust and ice.
Some comets are only visible by the aid of the telescope, while others can be seen by the naked eye. In the latter case they usually appear like stars accompanied with a train of light, sometimes short and sometimes extending over half the sky, mostly single and more or less curved, but sometimes forked. In a comet which appeared in 1744 the train was divided into several branches, spreading out from the head like a fan. The train is not stationary relatively to the head, but is subject to remarkable movements. The direction in which it points is always opposite to the sun, and as the , comet passes its perihelion the train changes its apparent position with extraordinary velocity. The head of the comet is itself of different degrees of luminosity, there being usually a central core, called the nucleus, of greater brilliancy than the surrounding envelope, called the coma.
Comets were long regarded as supernatural objects, and usually as portents of impending calamity. Tycho Brahe was the first who expressed a rational opinion on the subject, coming to the conclusion that the comet of 1577 was a heavenly body at a greater distance from the earth than that of the moon. The general law of the motion of bodies, as well as his own observations on the comet of 1680, led Isaac Newton to conclude that the orbits of the comets must, like those of the planets, be ellipses, having the sun in one focus, but far more eccentric; and having their aphelions, or greater distances from the sun, far remote in the regions of space.
This idea was taken up by Halley, who collated the observations which had been made of all the twenty-four comets of which notice had been taken previous to 1680. The results were very interesting. With but few exceptions the comets had passed within less than the earth's shortest distance from the sun, some of them within less than one-third of it, and the average about one-half. Out of the number, too, nearly two-thirds had had their motions retrograde, or moved in the opposite direction to the planets. While Halley was engaged on these comparisons and deductions the comet of 1682 made its appearance, and he found that there was a wonderful resemblance between it and three other comets that he found recorded - the comets of 1456, of 1531, and of 1607. The times of the appearance of these comets had been at very nearly regular intervals, the average period being between seventy-five and seventy-six years. Their distances from the sun, when in perihelion, or when nearest to that luminary, had been nearly the same, being nearly six-tenths of that of the earth, and not varying more than one-sixtieth from each other.
The inclination of their orbits to that of the earth had also been nearly the same, between 17 degrees and 18 degrees; and their motions had all been retrograde. Putting these facts together, Halley concluded that the comets of 1456, 1531,1607, and 1682 were reappearances of one and the same comet, which revolved in an elliptic orbit round the sun, performing its circuit in a period varying from a little more than seventy-six years to a little less than seventy-five; or having, as far as the observations had been carried, a variation of about fifteen months in the absolute duration of its year, measured according to that of the earth. For this variation in the time of its revolution Halley accounted upon the supposition that the form of its orbit had been altered by the attraction of the remote planets Jupiter and Saturn as it passed near to them; and thence he concluded that the period of its next appearance would be lengthened, but that it would certainly reappear in 1758 or early in 1759. As the time of its expected reappearance approached, Clairaut calculated that it would be retarded 100 days by the attraction of Saturn, and 518 by that of Jupiter, so that it would not come to the perihelion, or point of its orbit nearest the 500 sun, until the 13th of April, 1759.
It actually reached its perihelion on the 13th of March, 1759, being thirty days earlier than he had calculated. Along with the period of this comet and its perihelion distance, the magnitude and form of its path were also calculated. Estimating the mean distance of the earth from the sun at 95,000,000 miles (the number which was at that time considered as the true one), the mean distance of the comet was calculated to be 1,705,250,000 miles; its greatest distance from the sun, 3,355,400,000; its least distance, 55,100,000; and the transverse or largest diameter of its orbit, 3,410,500,000. This comet, therefore, is a body belonging to the solar system, and quite beyond the attraction of any body which does not belong to that system; and as this is determined of one comet, analogy points it out as being the case with them all. In 1835 it again returned, being first seen at Rome, on August the 5th, and from that time continued to be observed until the end of the year in Europe, and through a great part of spring 1836 in the southern hemisphere.
The comet denominated Encke's comet, which has made repeated appearances, was first observed in 1818, and was identified with a comet observed in 1786, also with a comet discovered in 1795 by Miss Herschel in the constellation Cygnus, and with another seen in 1805. Its orbit is an ellipse of comparatively small dimensions, wholly within the orbit of Jupiter; its period is 1260 days, or about three years and three-tenths. It has been frequently observed since.
Another comet, the history of which is of the utmost importance in the latest theories regarding the connection of these bodies and the periodic showers of shooting-stars, is one known as Biela's comet, discovered in 1826. It revolved about the sun in about 6.75 years, and was identified as the same comet which was observed in 1772 and in 1806. Its returns were noted in 1832, 1839, and 1845. In 1846 it divided into two, returned double in 1852, but has not since been seen, the Supposition being that it has been dissipated, and that it was represented by a great shower of meteors that were seen in November 1872. One of the most remarkable comets of recent times was that known as Donati's, discovered by Dr. Donati of Florence in 1858. It was very brilliant in England in the autumn of that year, and on the 18th of October was near coming into collision with Venus, The year 1881 was remarkable for the number of comets recorded. During that year no fewer than seven comets, including the well-known short-period comet Encke's, were observed. Research Comet
Hemlock (Conium maculatum) is a poisonous biennialherb of the family Umbelliferae supposed to be identical with the plant koneion of the Greeks.. It is a tall, erect, branching biennial, with a smooth, shining, hollow stem usually marked with purple spots. It has elegant, much divided leaves which when bruised emit a nauseous odour. The flowers are white in compound umbels of ten or more rays surrounded by a general involucre of three to seven leaflets.
Hemlock is found in Britain and throughout Europe and temperate Asia in waste places, banks, and under walls. It is said to be fatal to cows when they eat it, but that horses, goats, and sheep may feed upon it without danger. In the human subject it causes paralysis, convulsions, and death. The poison administered to Socrates is supposed to have been a decoction of it, though others are of opinion that the potion was obtained from water-hemlock (Cicuta virosa).
Hemlock is a powerful sedative, and is used medicinally. The extract is considered the best preparation. It was formerly used as a substitute for, or as an accompaniment to opium. It has been found very useful in chronic rheumatism and in hooping-cough, in allaying the pain of irritable sores and cancerous ulcers. The virtues of hemlock reside in an alkaline principle termed coma or coniine. Research Hemlock
Berenice was the wife of Ptolemy Euergetes. When her husband went to war in Syria she vowed that if he returned safe she would dedicate her hair to the gods. Upon his safe return she hung her hair in the temple of Venus, from where it disappeared and is said to have been used to form the constellationComa Berenices. Research Berenice
Acidosis is a condition in which the body fluids tend to have a higher acid content than normal. The body has a variety of ways to compensate for mild acidosis, but prolonged acidosis can produce weakness, headache, and heavy or rapid breathing. Severe acidosis may lead to acidemia (a build-up of acids in the blood) which can result in coma and death. Acidosis itself is not a disease, but it may warn of the presence of a disease. It arises from disorders that cause the body to accumulate excess acid or to lose too much alkali. Most of these disorders are respiratory failures or metabolic failures. Respiratory acidosis results from such disturbances as severe lung disease, blockage of the upper air passages, and chest injury. Metabolic failures involve malfunctioning of the process by which the body changes food into energy and tissue. Metabolic acidosis arises from kidney failure, diabetes, poisoning, and severe diarrhoea. Treatment usually consists of correcting the underlying problem and administering sodium bicarbonate or another alkaline substance through a vein. Research Acidosis
Alkalosis is a condition in which a person's body fluids become too alkaline. The body adjusts to mild alkalosis but severe alkalosis can result in muscular weakness, convulsions, coma, and even death. Most cases of alkalosis arise from disorders or drugs that cause the body to lose too much acid, thus upsetting the normal balance of acid and alkali. Disorders that can result in alkalosis include prolonged vomiting and hyperventilation. Prolonged alkalosis causes excessive loss of hydrochloric acid from the stomach. During hyperventilation, a person exhales too much carbon dioxide, lowering the level of carbonic acid in the blood.
Alkalosis can arise from the prolonged use of such drugs as diuretics. Treatment of alkalosis usually consists of correcting the underlying disorder or reducing the drug intake. A solution containing a weak acid may be administered through a vein to help restore the body's normal acid- alkalibalance. Research Alkalosis
Anaphylaxis is a severe, allergic reaction, usually to an insect bite or sting, or to a food (for example, strawberries or onions). It is characterised by itching, rash, hives, runny nose, wheezing, paleness, cold sweats, low blood pressure, coma, or even cardiac arrest. Research Anaphylaxis
Aneurysm is a balloon-like bulge that forms in a weakened area of the wall of an artery or vein. The most dangerous aneurysms are those that form in arteries, especially the arteries of the brain and the aorta. Most aneurysms result from atherosclerosis, a disease caused by cholesterol build-up in artery walls. Other causes of aneurysms include genetic disorders or other defects present at birth. The symptoms of an aneurysm vary with its location and size. There may be no symptoms, or pain may develop at the site of the aneurysm. Shortness of breath occurs if the aneurysm interferes with the heart's pumping ability. Some aneurysms press on nearby structures, producing a cough, hoarseness, or difficulty in swallowing. An aneurysm may worsen without the patient knowing and then suddenly rupture, causing a coma, paralysis, or death. Many strokes result from the rupture of an aneurysm in an artery of the brain.
Aneurysms can be detected with X-rays and, in many cases, can repair them surgically. Surgeons remove the diseased portion of the blood vessel. If it is a minor vessel, they tie off the loose ends. In a major artery or vein, they replace the diseased portion with a plastic tube, a fabric patch, or a piece of another blood vessel. Research Aneurysm
Chloral hydrate is a white crystalline solid with a faint odour used in medicine as a hypnotic since 1869. Related to chloroform, chloral hydrate is not as strong as some of the more recent drugs in this category, but administered with alcohol, the crystalline powder - the so-called 'knockout drops' - can produce coma. Chloral hydrate also irritates mucous membranes and skin. Research Chloral hydrate
Abbreviations
Research Coma Berenices
