Magnetic Declination (1600–ca. 1692): Magnetism has long been recognized as an important force of nature. Historically, magnetism was known to the ancient Greeks as early as the 7th century B.C.E. Around that time the Greek philosopher Thales made some descriptions of the properties of lodestone, a magnetic ore. However, it was the ancient Chinese who made some of the first technological advances associated with magnetism when they recognized that lodestone would orient itself in a north-south configuration. Some believe that the 13th-century Italian explorer Marco Polo (ca. 1254–1324) was responsible for bringing the Chinese lodestone compass back to Western culture. In the time between these cultures and the 17th century magnetism was primarily associated with the practice of medicine, where it was believed to help cure certain ailments. In the 17th century the English physician William Gilbert conducted the first true scientific studies of magnetism. Not only did Gilbert recognize magnetism as a force of nature, he also distinguished its attractive force from that of electricity (see MAGNETISM). From a historical perspective Gilbert’s work is frequently recognized as one of the first in the scientific revolution of the Renaissance to employ the scientific method (see SCIENTIFIC REASONING) and as such had a tremendous influence on the science of the 17th century.
Prior to the 17th century sailors had discovered that the needle of a magnetic compass does not point directly north, but typically displays some small degree of error. This error was commonly called the variation of the compass, or magnetic declination. Furthermore, that degree of error was not a constant, and was dependent on the location where