A History of Inventions, Discoveries, and Origins, Volume I (of 2)
TekstSYMPATHETIC INK
If we give this name to any fluid, which when written with, will remain invisible till after a certain operation, such liquids were known in very early periods. Among the methods, with which Ovid teaches young women to deceive their guardians, when they write to their lovers260, he mentions that of writing with new milk, and of making the writing legible by coal-dust or soot. Ausonius proposes the same means to Paulinus261; but his commentators seem not to have fully understood his meaning; for favilla is not to be explained by favilla non modice calida, as Vinetus has explained it, but by fuligo. That word is often employed by the poets in the same sense. As a proof of it, Columella, speaking of the method, not altogether ineffectual, and even still used, of preserving plants from insects by soot, calls it nigra favilla; and afterwards, when mentioning the same method, free from poetical fetters, he says fuliginem quæ supra focos tectis inhæret262. It may be easily perceived, that instead of milk any other colourless and glutinous juice might be employed, as it would equally hold fast the black powder strewed over it. Pliny, therefore, recommends the milky sap of certain plants for the like purpose263.
There are several metallic solutions perfectly colourless, or, at least, without any strong tint, which being used for writing, the letters will not appear until the paper be washed over with another colourless solution, or exposed to the vapour of it; but among all these there is none which excites more astonishment, than that which consists of a solution of lead in acetic acid, and which by sulphuretted hydrogen gas becomes black, even at a considerable distance. This ink, which may be employed by conjurers, proves the subtlety of this gas, and the porosity of bodies; as the change or colouring takes place, even when the writing is placed on the other side of a thin wall.
This effect presented itself perhaps accidentally to some chemist; but the discovery is not of great antiquity. Wecker, who compiled his book De Secretis from Porta, Cardan, and several old writers, and printed it for the first time in 1582, and gave a third edition in 1592, must have been unacquainted with it; else he certainly would not have omitted it in the fourteenth book, where he mentions all the methods of secret writing. Neither would it have been unnoticed by Caneparius, whose book De Atramentis was printed at Venice, for the first time, in 1619.
The first person who, as far as I have been able to learn, gave a receipt for preparing this ink, was Peter Borel, in Historiarum et Observationum Medico-physic. Centuriæ quatuor. In this work, which was printed for the first time in 1653, and a second time in 1657, at Paris, and of which there were several editions afterwards, the author calls it a magnetic water, which acts at a distance264. After the occult qualities of the schoolmen were exploded, it was customary to ascribe phænomena, the causes of which were unknown, and particularly those the causes of which seemed to operate without any visible agency, to magnetic effluvia; as the tourmaline was at first considered to be a kind of magnet. Others concealed their ignorance under what they called sympathy, and in latter times attraction and electricity have been employed for the like purpose. Borel, who made it his business to collect new observations that were kept secret, learned the method of preparing this magnetic water from an ingenious apothecary of Montpelier, and in return taught him some other secrets. Otto Tachen, a German chemist265, afterwards thought of the same experiment, which he explains much better, without the assistance of magnetism or sympathy. The receipt for making these liquids, under the name of sympathetic ink, I find first given by Le Mort266, and that name has been still retained267.
Another remarkable kind of sympathetic ink is that prepared from cobalt, the writing of which disappears in the cold, but appears again of a beautiful green colour, as often as one chooses, after being exposed to a moderate degree of heat.
The invention of this ink is generally ascribed to a Frenchman named Hellot. He was, indeed, the first person who, after trying experiments with it, made it publicly known, but he was not the inventor; and he himself acknowledges that a German artist of Stolberg first showed him a reddish salt, which, when exposed to heat, became blue, and which he assured him was made out of Schneeberg cobalt, with aqua regia268. This account induced Hellot to prepare salts and ink from various minerals impregnated with cobalt; but A. Gesner proved, long after, that this ink is produced by cobalt only, and not by marcasite269.
When Hellot’s experiments were made known in Germany, it was affirmed that Professor H. F. Teichmeyer, at Jena, had prepared the same ink six years before, and shown it to his scholars, in the course of his lectures, under the name of sympathetic ink270. It appears, however, that it was invented, even before Teichmeyer, in the beginning of the last century by a German lady. This is confirmed by Pot, who says that the authoress of a book printed in 1705, which he quotes under the unintelligible title of D. J. W. in clave, had given a proper receipt for preparing the above-mentioned red salt, and the ink produced by it271. If it be true that Theophrastus Paracelsus, by means of this invention, could represent a garden in winter, it must be undoubtedly older272.
[In consequence of the progress of modern chemistry and the discovery of a vast number of new chemical compounds, sympathetic inks may be made in an almost endless number and variety. The principal may be classed in the following manner: – 1, such as when dried upon paper being invisible, on moistening with another liquid become again evident: of this kind there are a vast number; among which we may mention a solution of a soluble salt of lead, or bismuth, for writing, and a solution of sulphuretted hydrogen for washing over; the writing then appears black; or green vitriol for writing and prussiate of potash for washing over, when the writing becomes blue273; 2, such as are rendered evident by being sifted over with some powder, as the milk with soot described above; 3, those which become visible by heat, such as characters in dilute sulphuric acid, lemon-juice, solutions of the nitrate and chloride of cobalt, and of chloride of copper; the two former become black or brown, the latter are rendered green, the colouring disappearing subsequently when allowed to cool in a moist place. Amusing pictures are sometimes made with these sympathetic inks, particularly those composed of cobalt; for if a landscape be drawn to represent winter, the vegetation being covered with a solution of cobalt, on holding the paper to the fire, all those portions covered with the solution appear of a bright green, and thus completely change the character of the scene.]
DIVING-BELL
The first divers learned their art by early and adventurous experience, in trying to continue under water as long as possible without breathing; and, indeed, it must be allowed that some of them carried it to very great perfection. This art, however, excites little surprise; for, like running, throwing, and other bodily dexterities, it requires only practice; but it is certain that those nations called by us uncultivated and savage excel in it the Europeans274, who, through refinement and luxury, have become more delicate, and less fit for such laborious exercises.
In remote ages, divers were kept in ships to assist in raising anchors275, and goods thrown overboard in times of danger276; and, by the laws of the Rhodians, they were allowed a share of the wreck, proportioned to the depth to which they had gone in search of it277. In war, they were often employed to destroy the works and ships of the enemy. When Alexander was besieging Tyre, divers swam off from the city, under water, to a great distance, and with long hooks tore to pieces the mole with which the besiegers were endeavouring to block up the harbour278. The pearls of the Greek and Roman ladies were fished up by divers at the great hazard of their lives; and by the like means are procured at present those which are purchased as ornaments by our fair.
I do not know whether observations have ever been collected respecting the time that divers can continue under water. Anatomists once believed that persons in whom the oval opening of the heart (foramen ovale) was not closed up, could live longer than others without breathing, and could therefore be expert divers. Haller279, however, and others, have controverted this opinion; as people who had that opening have been soon suffocated, and as animals which have it not can live a long time under water: besides, when that opening is perceptible in grown persons, it is so small as not to be sufficient for that purpose, especially as the ductus arteriosus is scarcely ever found open.
The divers of Astracan, employed in the fishery there, can remain only seven minutes under water280. The divers in Holland seem to have been more expert. An observer, during the time they were under water, was obliged to breathe at least ten times281. Those who collect pearl-shells in the East Indies can remain under water a quarter of an hour, though some are of opinion that it is possible to continue longer; and Mersenne mentions a diver, named John Barrinus, who could dive under water for six hours282. How far this may be true I shall leave others to judge.
[The various statements regarding the length of time during which divers can remain under water, unaided by apparatus for renewing the supply of atmospheric air, are not borne out by the experience of those who have carefully observed and noted these phænomena. The average time which human beings can remain in the water under these conditions, is one and a half or two minutes283; extraordinary cases are attested where five and even six minutes have elapsed, but these are exceedingly rare instances and far beyond the average; no instance of a longer time than this is recorded on credible authority. Some interesting remarks on this point were made not long since by a member of the Asiatic Society to Dr. Faraday. The lungs in their natural state are charged with a large quantity of impure air; this being a portion of the carbonic acid gas which is formed during respiration, but which, after each expiration, remains lodged in the involved passages of the pulmonary tubes. By breathing hard for a short time, as a person does after violent exercise, this impure air is expelled, and its place is supplied by pure atmospheric air, by which a person will be enabled to hold his breath much longer than without such precaution. Dr. Faraday states, that although he could only hold his breath, after breathing in the ordinary way, for about three-fourths of a minute, and that with great difficulty, he felt no inconvenience, after making eight or ten forced respirations to clear the lungs, until the mouth and nostrils had been closed more than a minute and a half; and that he continued to hold breath to the end of the second minute. A knowledge of this fact may enable a diver to remain under water at least twice as long as he otherwise could do. It is suggested that possibly the exertion of swimming may have the effect of occasioning the lungs to be cleared, so that persons accustomed to diving may unconsciously avail themselves of this preparatory measure.]
It is certain, however, that men began very early to contrive means for supplying divers with air under the water, and of thereby enabling them to remain under it much longer. For this purpose the diving-bell, campana urinatoria, was invented. Those who had no idea of this machine, might have easily been led to it by the following experiment. If a drinking-glass inverted be immersed in water, in such a manner that the surface of the water may rise equally around the edge of the glass, it will be found that the glass does not become filled with water, even when pressed down to the greatest depth; for where there is air no other body can enter, and by the above precaution the air cannot be expelled by the water. In like manner, if a bell of metal be constructed under which the diver can stand on a stool suspended from it so that the edge of the bell may reach to about his knee, the upper part of his body will be secured from water, and he can, even at the bottom of the sea, breathe the air enclosed in the bell.
The invention of this bell is generally assigned to the sixteenth century, and I am of opinion that it was little known before that period. We read, however, that even in the time of Aristotle divers used a kind of kettle to enable them to continue longer under water; but the manner in which it was employed is not clearly described.
The oldest information we have respecting the use of the diving-bell in Europe is that of John Taisnier, quoted by Schott284. The former, who was born at Hainault in 1509, had a place at court under Charles V., whom he attended on his voyage to Africa. He relates in what manner he saw at Toledo, in the presence of the emperor and several thousand spectators, two Greeks let themselves down under water, in a large inverted kettle, with a burning light, and rise up again without being wet. It appears that this art was then new to the emperor and the Spaniards, and that the Greeks were induced to make the experiment in order to prove the possibility of it. After this period the use of the diving-bell seems to have become still better known. It is described more than once in the works of Lord Bacon, who explains its effects, and remarks that it was invented to facilitate labour under the water285.
In the latter part of the seventeenth century the diving-bell was sometimes employed in great undertakings. When the English, in the year 1588, dispersed the Spanish fleet called the Invincible Armada, part of the ships went to the bottom near the Isle of Mull, on the western coast of Scotland; and some of these, according to the account of the Spanish prisoners, contained great riches. This information excited, from time to time, the avarice of speculators, and gave rise to several attempts to procure part of the lost treasure. In the year 1665, a person was so fortunate as to bring up some cannon, which, however, were not sufficient to defray the expenses. Of these attempts, and the kind of diving-bell used, an account has been given by a Scotsman named Sinclair286; but Paschius287, Leupold288 and others falsely ascribe the invention of this machine to that learned man. He himself does not lay claim to this honour; but says only, that he conversed with the artist and measured the machine.
Some years after attempts of the like kind were renewed. William Phipps, the son of a blacksmith, born in America in 1650, and who had been brought up as a ship-carpenter at Boston, formed a project for searching and unloading a rich Spanish ship sunk on the coast of Hispaniola, and represented his plan in such a plausible manner, that king Charles II. gave him a ship, and furnished him with every thing necessary for the undertaking. He set sail in the year 1683; but, being unsuccessful, returned again in great poverty, though with a firm conviction of the possibility of his scheme. He endeavoured, therefore, to procure another vessel from James II., who was then on the throne; but as he failed in this, he tried to find the means of executing his design by the support of private persons, and, according to the prevailing practice, opened for that purpose a subscription. At first he was laughed at; but at length the duke of Albemarle, son of the celebrated General Monk, took part in it, and advanced a considerable sum to enable him to make the necessary preparations for a new voyage. Phipps soon collected the remainder; and in 1687 set sail in a ship of two hundred tons burthen to try his fortune once more, having previously engaged to divide the profit according to the twenty shares of which the subscription consisted. At first, all his labour proved fruitless; but at last, when his patience was almost entirely exhausted, he was so lucky as to bring up, from the depth of six or seven fathoms, so much treasure, that he returned to England with the value of two hundred thousand pounds sterling. Of this sum he himself got about sixteen, others say twenty thousand, and the duke ninety thousand pounds. After he came back, some persons endeavoured to persuade the king to seize both the ship and the cargo, under a pretence that Phipps, when he solicited for his Majesty’s permission, had not given accurate information respecting the business. But the king answered, with much greatness of mind, that he knew Phipps to be an honest man, and that he and his friends should share the whole among them, had he returned with double the value. His Majesty even conferred upon him the honour of knighthood, to show how much he was satisfied with his conduct. This Phipps was afterwards high sheriff of New England, and died at London, greatly respected, in 1693. This affair was attended with such good consequences to the duke of Albemarle, that he obtained from the king the governorship of Jamaica, in order to try his fortune with other ships sunk in that neighbourhood. But whether it was that the gold had been already taken from the one before-mentioned, or that, when the vessel went to pieces, the sea had dispersed the cargo, it is certain that nothing further was found worth the labour of searching for289.
In England, however, several companies were formed, and obtained exclusive privileges of fishing up goods on certain coasts, by means of divers. The most considerable of these was that which, in 1688, tried its success at the Isle of Mull, and at the head of which was the earl of Argyle. The divers went down to the depth of sixty feet under water, remained there sometimes a whole hour, and brought up gold chains, money, and other articles, which, however, when collected, were of very little importance290. Without giving more examples of the use of the diving-bell, I shall now mention some of those who, in later times, have endeavoured to improve it. That this machine was very little known in the first half of the sixteenth century, I conclude from the following circumstance. To the oldest edition of Vegetius on the art of war, there are added, by the editor, some figures, of which no explanation is given in the book. Among these is represented a method of catching fish with the hands, at the bottom of the sea. The apparatus for this purpose consists of a cap, which is fitted so closely to the head of the diver that no water can make its way between; and from the cap there ascends a long leather pipe, the opening of which floats on the surface of the water. Had the person who drew these figures been acquainted with the diving-bell, he would certainly have delineated it rather than this useless apparatus291. Of the old figures of a diving machine, that which approaches nearest to the diving-bell is in a book on fortification, by Lorini; who describes a square box bound round with iron, which is furnished with windows, and has a stool affixed to it for the diver. This more ingenious contrivance appears, however, to be older than that Italian; at least he does not pretend to be the inventor of it292.
In the year 1617, Francis Kessler gave a description of his water-armour293, intended also for diving, but which cannot really be used for that purpose294. In the year 1671, Witsen taught, in a better manner than any of his predecessors, the construction and use of the diving-bell295; but he is much mistaken when he says that it was invented at Amsterdam. In 1679 appeared, for the first time, Borelli’s well-known work De Motu Animalium296, in which he not only described the diving-bell, but also proposed another, the impracticability of which was shown by James Bernoulli297. When Sturm published his Collegium Curiosum, in 1678, he proposed some hints for the improvement of this machine, on which remarks were made in the Journal des Sçavans (Jan. 1678). None, however, have carried their researches further for this purpose than Dr. Halley, and Triewald, a Swede.
The bell which Edmund Halley, secretary to the Royal Society, caused to be made, was three feet broad at the top, five feet at the bottom, and eight feet in height; forming a cavity of sixty-three cubic feet. It was covered with lead; and was so heavy that it sunk to the bottom, even when entirely empty. Around the lower edge, weights were disposed in such a manner that it should always sink in a perpendicular direction, and never remain in an oblique position. In the top was fixed a piece of strong glass to admit the light from above, and likewise a valve to give a passage to the air corrupted by the breath. Around the whole circumference of the bottom was placed a seat, on which the divers sat; and a stool, fixed to ropes, hung below, on which they could stand in order to work. The whole machine was suspended from a cross beam fastened to the mast of a ship, so that it could be easily lowered down into the water and again drawn up. That the bell might be supplied with fresh air under the water, large vessels filled with air, and which had an opening below through which the water compressed the included air, were let down by ropes. In the top of these vessels were leather pipes, besmeared with oil, through which the diver introduced air from the vessels into the bell; and as soon as a vessel was emptied, it was drawn up, on a signal made by the diver, and another let down. The foul air in the bell, being the warmest and lightest, rose to the top of the machine, where it was suffered to escape through the valve before-mentioned. By these means the bell could be continually supplied with fresh air in such abundance, that Halley, and four other persons, remained under water, at the depth of ten fathoms, an hour and a half, without suffering the least injury, and could, with equal security, have continued longer, or even as long as they might have wished. This precaution, however, is necessary, that the bell be let down at first very slowly, that the divers may be gradually accustomed to inspire the compressed air; and at every twelve fathoms the bell must be held fast, in order to expel the water which has rushed in, by letting fresh air into it. By such apparatus, Halley was enabled to make the bottom of the sea, within the circumference of the bell, so dry that the sand or mud did not rise above his shoe. Through the window, in the top, so much light was admitted, that when the sea was still and the waves did not roll, he could see perfectly well to read and write under the water. When the empty air-vessels were drawn up, he sent up with them his orders, written with an iron spike on a plate of lead, and could thus let those above know when he wished to be removed with the bell to another place. In bad weather, and when the sea was rough, it was as dark under the bell as at night; he then kindled a light; but a burning candle consumed as much air as a man. The only inconvenience of which Halley complained was, that, in going down, he felt a pain in his ears, as if a sharp quill had been thrust into them. This pain returned every time the bell was let down to a greater depth, but soon went off again. A diver thought to prevent this pain by putting chewed paper into both his ears; but the bits of paper were forced in so far by the air, that a surgeon found great difficulty to extract them.
Another improvement of the diving-bell was effected by the well-known Triewald, a Swede, in 1732. His bell, which was much smaller and more commodious, was made of copper, tinned in the inside. On the top there were panes of glass, which, for the greater security, were fixed in a frame of the same metal. The stool below was placed in such a manner, that the head only of the diver, when he stood upon it, rose above the surface of the water in the bell. This situation is much better than when the whole body is raised above the water in the bell, because near the surface of the water the air is much cooler and fitter to breathe in than at the top of the machine. That the diver also might remain conveniently in the upper part of the bell, Triewald arranged his apparatus so that when the diver had breathed as long as possible in the upper air, he found at the side of the bell a spiral pipe, through which he could draw in the lower cool air which was over the surface of the water. To the upper end of this copper pipe was affixed a pliable leather one, with an ivory mouth-piece, which the diver put into his mouth, and could thus inspire fresh air, in whatever position his body might be298.
[In 1776, Mr. Spalding of Edinburgh made some improvements in Dr. Halley’s diving-bell, for which he was rewarded by the Society of Arts. His diving-bell was made of wood, and was so light, that, with the divers and the weights attached to its rim, it would not sink; the weight necessary to counteract its buoyancy being added in the form of a large balance-weight, suspended from its centre by a rope, which was so mounted on pulleys that the divers could either draw the balance-weight up to the mouth of the bell or allow it to fall a considerable depth below it. Thus by letting the weight down to the bottom, the divers could, as it were, anchor the bell at any required level, or prevent its further descent if they perceived a rock or part of a wreck beneath it, which might otherwise overturn it. Also, by hauling in the rope while the weight was at the bottom, the persons in the bell might lower themselves at pleasure. Another improvement consisted in the addition of a horizontal partition near the top of the bell, which divided off a chamber, that might, by suitable openings and valves, be filled either with water or with air from the lower part of the bell, so as to alter the specific gravity of the whole machine, and thereby cause it to ascend or descend at pleasure. The bell was supplied with air by an apparatus resembling that of Dr. Halley, and ropes stretched across the bell were used instead of seats and platforms for standing on. Thus the persons in the diving-bell were enabled, in case of accident, to raise themselves to the surface without any assistance from above, and it was rendered so perfectly manageable, that it might be removed to a considerable distance from the point at which it descended; its outward motion and its return to the vessel for the purpose of being hauled up, being assisted by a long boat, which carried the signal lines and the tackle for working the air-barrels.
Mr. John Farey, junior, made an improvement in Spalding’s apparatus299. The upper chamber of the diving-bell is very strong and air-tight, without any openings for the admission of water. Two pumps are fixed in the partition, by which air may be forced into the upper chamber, whenever, during a pause in the descent, the lower chamber or the cavity of the bell is replenished with air. By this means, the upper chamber is made a reservoir of condensed air, from which the bell may be replenished with air, when it is desired to increase its buoyancy, by forcing out the water from the lower part. Hence also, the buoyancy of the bell may be at any time diminished, by pumping some of the air from it into the upper chamber, whereby the water will be allowed to enter to a greater height; and as this is effected without wasting the air, there is no danger of diminishing the buoyancy of the machine to a degree which would prevent it from rising, in case the suspending rope or chain should break.
Smeaton first employed the diving-bell in civil engineering operations in repairing the foundations of Hexham bridge in 1779. The bell was made of wood, and was supplied with air by means of a forcing-pump, which was fixed to the top, and threw in a gallon of air at a time; the river being shallow, the top of the bell was not covered with water300. In 1788 he used a cast-iron one in repairing Ramsgate harbour; a forcing-pump in a boat supplied air through a flexible tube. Since that time it has been frequently used by Rennie and others in submarine operations, recovering property from wrecks, blasting, &c. Mr. Rennie has moreover constructed apparatus for moving the bell in any direction.
In addition to the various forms of diving-bell, different water- and air-tight dresses have been invented to enable divers to remain in the water and perform various operations. Thus, Dr. Halley invented a leaden cap which covered the diver’s head; it had glass before it, and contained as much air as was sufficient for two minutes, and had affixed to it a thick pliable pipe, with the other end fastened to the bell, and which, at the cap, was furnished with a valve to convey fresh air to the diver from the bell. This pipe, which the diver was obliged to wind round his arm, served him also as a guide to find his way back to the bell301.
Mr. Martin states that a gentleman at Newton-Bushel, in Devonshire, invented an apparatus consisting of a large case of strong leather, holding about half a hogshead of air, made perfectly water-tight, and adapted to the legs and arms, with a glass in the anterior part, so that when the case was put on, he could walk about very easily at the bottom of the sea, and go into the cabin and other parts of a ship in a wreck, and deliver out the goods; and that he practised this method for forty years, and thereby acquired a large fortune and equal fame302.
M. Klingert also invented a similar kind of apparatus, and described it in a pamphlet published at Breslau in 1798. The armour was made of tin-plate, in the form of a cylinder, with a round end to enclose the head and body; also, a leather jacket with short sleeves, and a pair of water-tight drawers of the same, buttoned on the metal part, where they joined, and were made tight by brass hoops. Two distinct flexible pipes terminated in the helmet, and rose to the surface of the water; one was for inhaling, and terminated in an ivory mouth-piece, the other was for the escape of foul air. The body was kept down by weights.