Robert Norman’s The Newe Attractive (1581) was the most scientific study of magnetism and the magnetic compass between Petrus Peregrinus’ Epistola de magnete from 1269 and William Gilbert’s De Magnete from 1600 and like the former featured strongly in the latter.
As is all too often the case with comparatively minor Renaissance figures we know next to nothing about Robert Norman. His dates of birth and death are unknown and all that is known about his origins is that they were humble. According to his own account he spent eighteen or twenty years at sea before he settled down at Ratliffe (Ratcliff) part of the Manor and Ancient Parish of Stepney on the north bank of the Thames between Limehouse (to the east) and Shadwell (to the west), as an instrument maker and self-styled ‘hydrographer’.
Ratcliffe in earlier times was also known as “sailor town”. It was originally known for shipbuilding but from the fourteenth century more for fitting and provisioning ships. In the sixteenth century various voyages of discovery were supplied and departed from Ratcliffe, including those of Willoughby and Frobisher.
Wikipedia
Norman’s principal claim to fame is as the discoverer of the second deviation of the magnetic compass needle, after variation or declination, magnetic dip or inclination. This, as observed by Norman, was the fact that the compass needles that he made did not sit horizontally on the middle point but the north end dip down at the north end, as he described it in chapter three of his The Newe Attractive:
“…rising alwaies to finish and end the, before I touched the needle I found continually that after I touched the Irons … the North point … would bende under the Horizon…”
The modern definition:
Magnetic dip, dip angle, or magnetic inclination is the angle made with the horizontal by the Earth’s magnetic field lines. This angle varies at different points on the Earth’s surface. Positive values of inclination indicate that the magnetic field of the Earth is pointing downward, into the Earth, at the point of measurement, and negative values indicate that it is pointing upward. The dip angle is in principle the angle made by the needle of a vertically held compass. (Wikipedia)
Strictly speaking Norman was not the first to discover magnetic dip, that honour goes to the Franconian astronomer, mathematician and instrument maker, Georg Hartmann (1489–1564), who discovered it in 1544 and described it, with a lot of other information on magnetism and compasses, in a letter he wrote to Duke Albrecht of Prussia (1490–1568). However, he never published his discovery, and the letter to Albrecht only became known in the nineteenth century, so the laurels for the discovery are usually awarded to Norman. On a side note, Hartmann measured the magnetic variation of Rome in 1510 finding it to be 6°.
Norman first noticed the dip on a six-inch compass needle that he had manufactured and initially thought that it had been somehow spoilt during the making process. He devised a series of experiments to try and find the cause and discovered that the needle was OK, and the cause was some attractive power of the Earth. Having discovered that dip was a natural phenomenon and constructed a dip-circle and measured the angle of dip for London that he measured accurately as 71° 51’.
The discovery of magnetic dip and Norman’s invention of the dip-circle to measure it led to speculation that dip could be used to determine latitude by overcast skies in the same way that it had been hoped to determine longitude by magnetic variation. Although, the dip-circle became a standard piece of the navigator’s equipment throughout the seventeenth century its use to determine latitude never came about.
Having dealt with the phenomenon of magnetic dip in a scientific manner, Robert Norman also turned his attention to magnetic variation. He dismissed the widespread idea that variation was by proportion around the globe and could thus be used to determine longitude citing the observed vagaries of variation. His comments were based on twenty years of experience at sea and the fact that the only people who gave him reliable figures for variation were those engaged in the Muscovy trade, and these did not in any way support the thesis. His book appears to have been the first publication to have an illustration of a compass card with a true north south meridian and a true east west line and then a compass north south line and a false east west line explain and indicating variation.
One important aspect of Norman’s studies of the magnetic compass is that he changed the perception of what actually took place when a compass needle stopped swinging. In the first post in this series, we briefly touched upon the supposed places to which the needle was drawn or attracted, the North Pole, the Pole star, a magnetic mountain or island etc. Norman saw it differently, to quote William Gilbert in his De Magnete:
Robert Norman, an Englishman, posits a point and place to which magnet looks (but whereto it is) not drawn : toward which magnetised iron, according to him is collimated but does not attract it.
Norman also instructed mariners to ensure that their compasses and marine charts had been made by the same people in the same locations. This was to ensure that they were based on the same value for magnetic variation. A compass combined with a marine chart from two different locations based on different variation values could and did lead to serious navigation problems on the open sea. He included a table of five different sorts of sailing compasses with their corresponding marine charts.
The Newe Attractive contained other material useful to navigators. The 1585 second edition contained a Regiment of the Seas “exactlie calculated unto the minute” valid for thirty years and presented in the same form as Medina and William Bourne, which contained a wealth of useful information.
Robert Norman worked closely with William Borough (bap. 1536–1598), who I dealt with in the last episode, and who was comptroller of the queen’s ships, supplying him with instruments and knowledge. The Newe Attractive was dedicated to William Borough
and as I wrote in the episode on Borough the book contained Borough’s A Discourse on the Variation, which was specifically written to be included as an appendix.
This treated the problem of variation “both Practically and Mathematically,” for the enlightenment of the simple and also the learned sort of mariner. Borough’s text contains a lot of polemic on the necessity of learning mathematics for navigation and also urging mariners to determine and record compass variation on their voyages. For this purpose, Robert Norman designed and constructed a new, improved variation compass to make the task of determining variation easier. Borough also strongly supported Norman’s rejection of the idea that variation was by proportion around the globe.
The combined Norman/Borough book went through new expanded and improved editions in 1585, 1592, 1611, and 1614.
In 1584, Norman published a second book, The Safegard of Sailers, or, Great Rutter, a manual of coastal sailing mostly translated from Dutch sources but with additional content of his own.
This book was dedicated to Charles Howard, Earl of Nottingham and Lord High Admiral of England.
The main thing that distinguishes Robert Norman from other English writers on navigation, magnetism, and the compass in the sixteenth century is the systematic series of experiment that he designed and carried out first, to determine if magnetic dip was a real natural phenomenon and secondly to conceive and construct the dip circle to measure dip. In his ODNB article on Robert Norman, Jim Bennett[1] wrote:
Norman has attracted considerable interest on account of his self-conscious adoption of an experimental approach and his unusual application of instruments. He was deploying his dip circle at a time when instruments were associated not with natural philosophy but with applications of mathematics to practical arts. He was sensitive that, as an ‘unlearned mechanician’, he would scarcely have been expected to concern himself with an area of practical mathematics relevant to natural philosophy, but he vigorously asserted the worth of investigations by practical men, who had the relevant art ‘at their finger ends’, while their more learned critics were ‘in their studies amongest their bookes’. Norman saw himself and his fellow mechanics as heirs to the vernacular tradition of mathematical publication, exemplified by the works of Robert Recorde and Billingsley’s English translation of Euclid.
[1] Jim Bennett was a truly great historian of scientific instruments and history of science museum curator, first in Cambridge at the Whipple and then in Oxford at the History of Science Museum. Sadly he died last Saturday, 28 October 2023, whilst I was using his article to write this blog post.
The Renaissance Mathematicus 