Geophysics was only recognized as a special area of study in the 19th century. But, there were geophysicists in ancient history. The first magnetic compasses were made in the fourth century BC and the first seismoscope was built in 132 BC. Isaac Newton applied his theory of mechanics to the tides and the precession of the equinox. Instruments were developed to measure the Earth's shape, density and gravity field, as well as parts of the water cycle. In the 20th century, geophysical methods were developed for remote exploration of the solid Earth and the ocean.