**Edmond** **Halley**, born on 8th November 1656 and died 14th January 1742, was an English astronomer, geophysicist, mathematician, meteorologist, and physicist who is best known for calculating the orbit of the eponymous Halley’s Comet.

Halley didn’t actually discover the comet itself, rather, he was able to calculate that the comet sightings of 1456, 1531, 1607, and * 1682 *related to the

**same**comet, which he predicted would return in 1758. Halley did not live to witness the comet’s return, but when it did, the comet became generally known as

*.*

**Halley’s Comet**Between 1679 and 1680 Robert Hooke exchanged a series of letters with Isaac Newton. The letters covered a wide variety of scientific topics. In one of the letters, Hooke mentioned a hypothesis that the Sun exerted an inverse square force. Supposedly the Sun pulls on the planets, and this force gets stronger the closer you are to the Sun. Hooke claimed the force caused the elliptical orbits of the planets.

Newton replied he never heard of such a hypothesis. He thought about the problem and soon produced a proof that an elliptical orbit can result from an inverse square force. Newton was a very secretive man and began to view Hooke as a rival. He felt that Hooke didn’t have the mathematical skills to produce a proof himself and apparently saw no need to tell anyone that he had produced such a proof, especially Hooke (Newton was right, Hooke could not produce a proof).

In * 1682*, Halley was witness to a bright comet. Halley had collected his comet observations and observations of other astronomers. When Isaac Newton found out, he asked Halley for copies. But Halley didn’t focus on anything further with comets (at least not straight away).

A few years later Hooke told Halley about the inverse square hypothesis and claimed he had a proof (it is unlikely Hooke had a proof, but Halley couldn’t have known that). Halley viewed it as a challenge, but slowly realised he needed help.

Halley spent most of his time on lunar observations but was also interested in the problems of gravity. One problem that attracted his attention was the proof of Kepler’s laws of planetary motion. In August * 1684*, he went to Cambridge to discuss this with Isaac Newton, only to find that Newton had solved the problem already, without publishing the solution. Halley asked to see the calculations and was told by Newton that he could not find them, but promised to redo them and send them on later. Halley was understandably concerned that Newton may have been bluffing, as Hooke had done so recently. Newton eventually did submit his calculations to Halley, in a short treatise entitled,

*On the motion of bodies in an orbit.*

At the time, Cambridge had put almost their entire annual budget into the publication of a [failing] book called “A History of Fishes” [Historia Piscium]. So much of the universities funding went into this book, that they eventually did not have enough to even pay Halley’s wages, instead, they paid him with copies of their worst selling book.

After this initial meeting, Edmond Halley visited Newton frequently, over the course of these visits Newton showed Halley his proof as well as many other unpublished papers. Halley recognised the importance of the work[s] and returned to Cambridge to arrange its publication with Newton, who instead went on to expand it into his *Philosophiæ Naturalis Principia Mathematica*. Halley wanted Newton to publish. Newton was reluctant, but Halley was persistent. With a lot of encouragement from Halley, eventually, Newton’s masterpiece was published at Halley’s expense in * 1687*.

This is indeed one of the most important publications in the entire history of science, and it almost didn’t happen.

The significance of the working friendship between Halley and Newton is not to be under-estimated, however, Halley made a name for himself in science without needing to be in Newton’s shadow.

Although he did not invent it, Edmond Halley made significant improvements to the Diving Bell, to be used for salvage and long-term (several hours) underwater exploration. In Halley’s diving bell, the atmosphere is replenished by sending weighted barrels of air down from the surface. The first bell that he made in * 1691* was of little use for practical salvage work, as it was very heavy, but he made improvements to it over time, later extending his underwater exposure time to over 4 hours.

Halley also suffered one of the earliest recorded cases of middle ear barotrauma, as a result of his diving experiments.

In the same year [1691], at a meeting of the Royal Society, Halley introduced a rudimentary working model of a magnetic compass using a liquid-filled housing to damp the swing and wobble of the magnetised needle.

In * 1692*, Halley put forth the idea of a hollow Earth consisting of a shell about 500 miles (800 km) thick, two inner concentric shells and an innermost core, about the diameters of the planets Venus, Mars, and Mercury. He suggested that atmospheres separated these shells and that each shell had its own magnetic poles, with each sphere rotating at a different speed. Halley proposed this scheme to explain anomalous compass readings. He envisaged each inner region as having an atmosphere and being luminous (and possibly inhabited) and speculated that escaping gas caused the Aurora Borealis. We now know this is, of course, false, but may be credited as the “first” scientific hollow earth hypothesis.

In * 1693 *Halley published an article on life annuities, which included an analysis of age-at-death. This article allowed the British government to sell life annuities at an appropriate price based on the age of the purchaser. Halley’s work strongly influenced the development of actuarial science. The construction of the life-table for Breslau, which followed more primitive work by John Graunt, is now seen as a major event in the history of demography and finance.

In * 1694 *the Royal Society censured Halley for suggesting that the biblical story of Noah’s flood might be an account of a cometary impact.

In * 1698*, Halley was given command of the

*Paramour*, a 52 feet (16 m) pink, so that he could carry out investigations in the South Atlantic into the laws governing the variation of the compass. On 19 August 1698, he took command of the ship and, in November 1698, sailed on what was the first purely scientific voyage by an English naval vessel.

Halley thereafter received a temporary commission as a Captain in the Royal Navy, recommissioned the *Paramour* on 24 August 1699 and sailed again in * September 1699 *to make extensive observations on the conditions of terrestrial magnetism. This task he accomplished in a second Atlantic voyage which lasted until 6 September 1700 and extended from 52 degrees north to 52 degrees south. The results were published in

*General Chart of the Variation of the Compass*(

*). This was the first such chart to be published and the first on which isogonic, or Halleyan lines appeared. These are still in use today, in both meteorological (weather) maps and also topographic and oceanic cartography.*

**1701**In * 1716*, Halley suggested a high-precision measurement of the distance between the Earth and the Sun by timing the transit of Venus. In

*he discovered the proper motion of the “fixed” stars by comparing his astrometric measurements with those given in Ptolemy’s*

**1718***Almagest*.

*Arcturus*and

*Sirius*were two noted to have moved significantly, the latter having progressed 30 arc minutes (about the diameter of the moon) southwards in 1800 years.

Edmond Halley succeeded John Flamsteed in 1720 as Astronomer Royal, a position Halley held until his death.