John Theophilus Desaguliers

• 1683 – 1744

• Born in La Rochelle, France

• Moved to England as a child.

• Graduated from Christ Church,

Oxford University.

• He was a priest, freemason,

engineer and natural philosopher.

• Popularised Newtonian Sciences.

Desaguliers became experimental assistant to Isaac Newton in 1713 whilst at Oxford.

He soon made a name for himself as a public experimental lecturer in London.

• The Royal Society of London, founded in November 1660, is an educated society for science. It is the oldest such society in existence. It was established to be a place of research and discussion.

• Desaguliers became experimenter for the Royal Society, with Newton’s assistance, in 1714.

• Even today, the Society acts as a scientific advisor to the British government, receiving a parliamentary grant.

His popular lectures were intended to demonstrate Newton propositions to non-academic audiences.

Desaguliers was awarded the Society’s highest honour, the Copley medal, three times in 1734, 1736 and 1741. His most famous achievement was for discoveries of the properties of electricity.

Desaguliers was one of many who tried to provide introductory texts to Newton’s Principa.

Something Newton always refused to provide.

In 1720, Desaguliers translated,

Mathematical Elements of Natural

Philosophy, Confirmed by experiments:

or, An Introduction to Sir Isaac Newton’s

Philosophy, into English.

Not only was he able to translate the

work of continental Newtonians but also

produce translations of his own works,

spreading Newtonian philosophy further.

The Newtonian System of the world, the best model of government and Allegorical Poem - 1728

But Newton the unparallel’d, whose Name

No Time will wear out of the Book of Fame,

Caelestial Science has promoted more,

Than all the Sages that have shone before.

Nature compell’d, his piercing Mind, obeys,

And gladly shews him all her secret Ways;

‘Gainst Mathematicks she has no Defence,

And yield t’experimental Consequence:

His tow’ring Genius, from its certain Cause,

Ev’ry Appearance, a priori draws,

And shews th’ Almighty Architect’s unalter’d Laws.

Throughout his life, Desaguliers helped to publish and write many books about Experimental Philosophy. In 1734 his own book, Course of Experimental Philosophy, was published and became very popular.

Desaguliers’ Planetarium, was an instrument made ‘to shew the motion of

the heavenly bodies’. He is credited as the inventor of the planetarium, a model

of the solar system to show the relative motions of the planets.

Desaguliers as an engineerThe water supply in Edinburgh

The ventilation of the houses of parliament

The first Westminster bridge

Within the the Royal Society he

devised new experiments to

defend several of Newton’s claims,

such as the shape of the Earth.

At the time, Newton suggested

universal gravitation which meant

that the Earth’s rotation would

cause a slight flattening at the

poles, whereas at the time many

others believed the poles would

be elongated.

Universal GravitationIsaac Newton formulated the law of universal gravitation between two objects.

The law states that between two objects of masses m1 and m2, with centers of

mass a distance d apart, there is an attractive force magnitude.

G is the gravitational constant and in SI units has

a value of 6.67x10-11 kg-1 m3 s-1. The force F is

called the gravitation force.

The gravitational force of an object on the Earth’s

surface is often called the weight of the object.

Find the magnitude of the gravitational force of an object of

mass M on the Earth’s surface. Assume that the Earth is a

sphere of mass 5.98x1024 kg and a radius 6.37x106 m.

Do you recognise the answer?

G is the gravitational constant and has a value of 6.67x10-11 kg-1 m3 s-1.

We see that Newton’s universal law of gravitation gives the familiar rule of the force of gravity or the weight of an object of mass M as Mg, where g = 9.8ms-2.