Gravity Gallery

1689 Sir Isaac Newton portrait young

Sir Isaac Newton ( 4 January 1643 -31 March 1727). English physicist and mathematician. 18th Century Mezzotint portrait after the painting by Sir Godfrey Kneller 1689, with later colouring. It shows Newton in his prime and is the earliest of the portraits. Newton is famous for his laws of motion and gravitation and remains one of the greatest scientists of all time. His opus magnus was his "Philosophiae Naturalis Principia Mathematica". Other pursuits included optical physics, alchemy, religious and occult investigation, and preventing forgery while superintendant of the Royal Mint. He was widely viewed as an eccentric genius, but his human remains indicated mercury poisoning from his alchemy may have contributed to his instability. This version retains yellow age toning of original and is in the possession of the photographer

© PAUL D STEWART/SCIENCE PHOTO LIBRARY

Hydrometers and Hygrometers C017/3433

Plate from 18th century encyclopedia showing illustrations of hydrometers and hygrometers. A hydrometer is an instrument used to measure the specific gravity (or relative density) of liquids; that is, the ratio of the density of the liquid to the density of water. A hygrometer is an instrument used for measuring the moisture content in the environment. Humidity measurement instruments usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed. By calibration and calculation, these measured quantities can lead to a measurement of humidity

© DAVID PARKER/SCIENCE PHOTO LIBRARY

Newtons cradle, artwork

Newton's cradle, artwork. This device consists of a number of steel balls suspended from a frame (not seen) in a horizontal line. Here, one ball on the end (left) has been pulled back and allowed to swing forward and downward under gravity. When it impacts the stationary line of balls, its momentum is transferred along the line, causing the ball on the opposite end to move upwards to a similar height. This sequence of impacts continues until all the initial energy has been lost to friction and sound. This apparatus, often used as a desk toy, demonstrates the conservation of momentum and energy

© DETLEV VAN RAVENSWAAY/SCIENCE PHOTO LIBRARY