C J L MARR

Sir Isaac Newton

an article written in 2005

 

Isaac Newton was born in January 1643, in Woolsthorpe Manor, Lincolnshire.  His father, an uneducated but wealthy man, died 3 months before Isaac was born.  His mother, Hannah Ayscough, remarried a local church minister when Isaac was 2 years old, and the young lad was sent to live with his grandmother, Margery Ayscough.  He felt very bitter toward his mother and stepfather for making him virtually an orphan, and his childhood was not a happy one.

Isaac attended the Free Grammar School in nearby Grantham where he was described as "idle" and "inattentive".  After his stepfather died, his mother decided to take him out of school and gave him control of her affairs and her estate, but he had no talent and no interest in the role.  His uncle, William Ayscough, wanted Isaac to enter university, so persuaded his mother to let him return to school to complete his initial education, and he finally entered Trinity College, Cambridge, in 1661.

He graduated in April 1665, but there was still no sign of anything more than an enquiring mind, and certainly no indication of any scientific genius at this time.  Two months later, the University closed because of the plague, and Isaac returned to Woolsthorpe.  Cambridge re-opened in 1667, and he returned, but in that two year period, Isaac had begun revolutionary advances in mathematics, optics, physics and astronomy. During this time, among other things, he concluded that white light was not at all a simple entity, formulated early versions of his three laws of motion, and discovered the law of centrifugal force on a body moving uniformly in a circular path.  He had blossomed!

Ever since Aristotle, scientists had thought of white light as a single entity.  Young Isaac fed white light through a prism and out came the spectrum of colours, so he concluded that white light was a mixture of many types of light ray which are all refracted at slightly different angles, with each different type of ray having a different spectral colour.  With this theory he was getting close to the truth, but unfortunately he also claimed that light was carried along by the motion of particles rather than waves.  Oddly, when he published his work on optical research (called "Opticks") in 1704, he had to use a wave theory of light to explain some of his observations, so once again he was close to the truth.  Nevertheless, such was his reputation that his particle theory was the accepted truth until the 19th century, when the wave theory started to gain popularity.

Newton realised that the chromatic aberration he saw in a telescope's lens was not the result of a problem with the lens.  In fact, because of his belief in the composition of white light as mentioned above, he wrongly maintained that the problem would exist in any lens.  It was this belief that led him to invent the Newtonian telescope, which uses mirrors rather than lenses.

Whereas the Newtonian telescope might be one of the most significant discoveries as far as the modern amateur astronomer is concerned, Newton's greatest gift to human science was the three laws of motion, and an understanding of the nature of gravity.

Isaac thought about the motion of the Moon, and realised that there must be an attractive force pulling it toward Earth's centre, otherwise it would simply continue moving in a straight line and leave orbit.  He recognised that the same force caused apples to fall from trees, and concluded that gravity was a universal force dependent only on the masses of the objects concerned and the distance between their centres.  This distance obeyed an inverse square law, such that if the Moon was twice as far from Earth, the force of gravity between them would be four times less and if the Moon was three times as far away, the gravitational pull would be nine times less.

Having the ability to visualise the nature of gravity, it would have been a simple step forward for Newton to conclude his three laws of motion :

• A body continues at rest or in uniform motion in a straight line unless acted upon by some force.

• A body's change of motion is proportional to the force acting on it and is in the direction of the force.

• When one body exerts a force on a second body, the second body must exert an equal and opposite force back on the first body.

With the publishing of "Philosophiae Naturalis Principia Mathematica", more commonly known simply as "Principia", in 1687, which laid out his new physics, Newton propelled astronomy from guesswork and mumbo-jumbo into an exact science where evidence could support theory.  Suddenly, so many things could be explained and calculated.  Things like the precession of Earth's axis, the eccentric orbits of comets, tides, and the motion of the Moon as perturbed by the Sun, could all be fully explained for the first time, and their effects calculated.

Newton wrote : “If I have seen farther than other men, it is because I stood upon the shoulders of giants”.  He realized he had simply extended the discoveries and theories of “giants” like Copernicus, Brahe, Keppler and Galileo.

Isaac Newton was knighted in 1705 by Queen Anne, thereby becoming the first scientist to receive such an honour.  In hindsight, he deserved a great deal more recognition than that since, when he died in 1727, his legacy to humankind was the basis of modern science.