Schott's Technica Curiosa, Nuremberg, 1664, and giving a history of the descent of two Greeks in a diving-bell, in a very large kettle, suspended by rope, mouth downward ; which was in 1538, at Toledo, in Spain, and in the presence of the Emperor Charles V.
Beckman cites a print in editions of Vegetius on War, dated in 1511 and 1532, in which the diver is represented in a cap, from which rises a long leather pipe, terminating in an opening which floats above the surface of the water.
Dr. Halley, about 1717, made a number of improvements in the diving-bell, and among them a leather cap for the head of the diver, with windows in front for the eyes.
This helmet was used by the diver when he left the bell, from which he received a supply of air through a flexible tube.
The essential parts of submarine armor consist of a helmet and a protection for the body.
These are rendered necessary by the great pressure of the water even at moderate depths.
For instance, at a depth little e
prior to the year 700.
Bells were first cast in England in the reign of Edmund, A. D. 940.
In A. D. 610, Clotaire II., king of France, besieged Sens, when Lupus, Bishop of Orleans, ordered the bells of St. Stephen to be rung.
The sound so frightened Clotaire that he gave up the siege.
So they say.
Pope John IX.
ordered bells to be rung as a defence against thunder and lightning, A. D. 900.
All the bells in Europe were rung in 1456, by order of Pope Calixtus III., to scare away Halley's comet, which was supposed to be in some way identified with Mohammed II., who had just taken Constantinople.
The comet left, but Mohammed stayed.
Most of the bells of Western Europe appear to have been hand-bells, of which some curious examples are still preserved.
They are made of thin plates of hammered iron, bent into a four-sided form and brazed together at the corners.
One of these, said to have belonged to St. Patrick, is preserved in the city of Belfast.
For a long period the
jection of the surface of the earth in the plane, with the meridians parallel to each other, the degrees of longitude all equal, and the degrees of latitude increasing in a corresponding ratio towards the poles.
It was introduced by Gerald Mercator in 1556.
The principle of its construction had, however, been previously explained by Edward Wright.
The first computation of longitude from the meridian of Greenwich Observatory was in 1679.
The first magnetic chart was constructed by Dr. Halley, in 1701.
It was limited to the Atlantic and Indian Oceans.
An instrument for measuring maps and charts.
1. (Printing.) A rectangular iron frame (a, Fig. 1255) which receives the matter from a galley, and in which it is arranged in columns or pages, and locked up in order for printing.
Rules (if necessary) and furniture for spacing the pages are placed between the pages, and all locked firmly in the chase by wedges c c c, called quoins.
e Spanish Armada by the Laird of Melgim, near the Isle of Man, but not sufficient to pay. Previous unsuccessful attempts had been made by Colquhoun, of Glasgow, who depended for air upon a leathern tube reaching above the surface of the water.
Dr. Halley, in 1715, improved the diving-bell by a contrivance for supplying it with fresh air by means of barrels lowered from the vessel, from which the bell was suspended, the foul air escaping by a cock.
This also allowed the bell to be completely filled with air, rendering the whole of its interior space available.
Halley also invented a waterproof cap to which pipes leading to the bell were attached, so that an operator could leave the bell and walk on the bottom outside, being supplied with air by the pipe.
This resembled in some respects the modern submarine armor, helmet, and diving-dress, which had been in occasional use since early in the sixteenth century (ut supra). Spalding, in 1774, made farther improvements by suspending a bal
r actually laid down and that which should be contained in a quadrant of the circle.
Dr. Hooke proposed the employment of an endless screw for dividing the edge of his quadrant, and this was actually used by Tompion in graduating Flamsteed's sector, probably under the supervision of Hooke.
Graham, who attained great reputation as an instrument-maker as well as clock-maker, adopted the principle of continuous bisections by means of a beamcompass.
In the instruments constructed by him for Halley and Bradley, the are of 60° was divided into 64 parts, making 96° instead of 90° to the quadrant.
It was deemed preferable to make the proportionate correction on each angle, rather than to trust to the uncertainty of a division to thirds or fifths.
Bird, 1750, subsequently improved the system by constructing scales of equal parts, enabling him to preserve the division of 90° by successive bisections.
His manual skill and care procured him merited reputation as a maker of accurate instr
He contrived the dipping-needle, suspended on a horizontal axis, and found the dip at London to be 71° 50′.
Robert Halley, in 1700, published a chart, having lines passing through points of equal magnetic variation.
His remark was that ofat may be confided in, and to propose hypotheses which after-ages may examine, amend, or refute.
Magnetic changes made Halley's chart obsolete in forty years, and it was reconstructed by the joint efforts of the English navy, East India Company, aLike other magnetic lines, it appears to have shifted.
Hansteen's observations confirmed in great detail the position of Halley, that the whole magnetical system is in motion; that the moving force is very great, extending its effects from pole to pude and zenith distance of the sun.
Among celebrated instruments may be mentioned the mural circle made by Graham, for Halley, at Greenwich, and those made by Ramsden in 1788, for Piazzi, at Palermo, and one for Dublin.
n 1590, Davis dispensed with the plumb and adapted the quadrant for use at sea.
Previous to this the astrolabe and mariner's cross had been universally employed by seamen for determining the latitude; the longitude was derived from dead reckoning or guess-work.
The telescope was adapted to the astronomical telescope by Picard.
All these old forms were superseded for nautical purposes by the reflecting quadrant, invented by Sir Isaac Newton, 1670.
He communicated the invention to Dr. Halley, who failed to give it publicity, and it was reinvented by Godfrey of Philadelphia, and also by Hadley in England.
An instrument constructed on Hadley's plan was submitted to the Royal Society in 1742, and from having been first made known by Hadley, the reflecting quadrant has been generally called Hadley's.
This and all similar reflecting instruments are based on the fact that the angle between the first and last directions of a ray which has undergone two reflections in the same pla
hen withdrawn from time to time through the plugged opening d and run into molds.
See also arsenic-furnace, Fig. 373, page 162; condenser, Fig. 1420, page 608.
A device to enable persons to work under water.
The diving-bell is said to have been used among the Greeks in the time of Aristotle.
It was first introduced into Western Europe near the beginning of the sixteenth century, but was not made practically available for use at considerable depths until Dr. Halley, in 1715, invented the method of displacing the water which entered the lower part of the bell by submerging casks containing air to a level a little below the bell, and discharging the air from them into it by admitting water at their bottoms by means of cocks.
He also contrived a headpiece, open at the lower part, which enabled a diver to leave the bell and make explorations outside, being supplied with air through a flexible tube leading into the bell.
Spalding subsequently divided th
Boyle suggested a fixed point obtained by thawing oil of anise-seed, as it was, unlike ice, always procurable.
Hooke suggested freezing water as one point.
Halley proposed spirit boiling as another point.
Newton suggested the boiling point of oil, as the range would be so much increased.
He next suggested melting ice anbitrary number of degrees which were to be continued up and down.
These standards obtained general acceptance.
The use of mercury in the tube was suggested by Halley, about 1697.
This fluid is very convenient for the purpose, as having a range of over 700° Fah. between its freezing and boiling points, and expanding very nearly uniformly with equal increments of heat.
Fahrenheit, a native of Dantzic, established as an instrumentmaker at Amsterdam, first practically carried out Halley's suggestion.
He divided the space between the freezing and boiling points of water into 180°, and commenced the graduation of his scale at the point to which the merc
The cosmographer Alonso de Santa Cruz, one of the instructors of Charles V., undertook the drawing up of the first general Variation chart, although indeed from very imperfect observations, as early as 1530, or a century and a half before Halley.
The movement of the magnetic lines, the first recognition of which is usually ascribed to Gassendi, was not even yet conjectured by William Gilbert; but at an earlier period Acosta, from the information of Portuguese navigators, assumed four and would soon be far removed from its first-observed position.
It was reserved for a future age to show the incorrectness of the then received opinion that magnetism is an effluvium issuing forth from the root of the tail of the Little Bear.
Halley, in 1683, sketched his theory of four magnetic poles or points of attraction, and of the periodical movement of the magnetic lines of no variation.
In 1698-1702 he made several voyages of observation, and the result was a general variationchart,