**Phythagoras (570-497 B.C.)**

He was born at Somos. He was a mathematician and an experimenter. He is known to common man through a geometric theorem which carries his name. He introduced the abstract idea of number. He regarded the Earth, the sun and the Moon as spheres.

**Socrates (469-399 B.C.)**

He was born in Athens in the house of a sculptor. He was regarded as the wisest philosopher of his time. His fields of interest were music, mathematics and gymnastics. He gave meanings to goodness, justice and similar ideas, which seem so simple but are so difficult to define. Plato (428-347 B.C.) was his famous disciple.

**Aristotle (384-322 B.C*)**

He was the son of a physician and disciple of Plato. He contributed mainly in the fields of physics, biology and the humanities. He mentioned about 500 animals, some with diagrams, gained bythin dissection. He described the development of

**Isaac Newton (A.D. 1642-1727)**

He was born in England on Christmas Day, 1642.

His main fields of interests were physics and mathematics. Laws of motion and Force of Gravity gave him an immense popularity. He invented the calculus or ‘flusion’s — finding the rate of change of one variable with respect to another. He never married in his life. He made a triangular prism and showed the dispersion of white light into seven colours; red, orange, yellow, green, blue, indigo and violet — this proved the composite nature of white light.

**Charles Darwin (A.D. 1809-1882)**

He was born at Shreusbury, Englandin 1809. He enriched his observations by collecting more facts, performing experiments, on breeding and variation in plants and animals.

The essential features of Darwin’s theory can be summed up in the following points.

There is intra-specific competition among individuals in a species and among species. There is a struggle for existence.

**Galileo Galilei (A.D. 1564-1642)**

He was born at Pisa, Italy in 1564. He invented the universal method of physical research by combining observation and induction with mathematical deduction tested by experiments. He was the only first man to find out that the path of a projectile would he a parabola. He was always fascinated in devising various instruments and pieces of machinery – this led him to invent telescope in 1609.

He detected the presence of black spots on the moon as hills and valleys and spots of the Sun with his telescope. He also discovered the principle of pendulum. His observations confirmed his belief that the Earth rotates about its axis and moves around the Sun. It- is interesting to point out that the most modern version of Galileo’s telescope, known as Hubble Space Telescope (cost $ 1.5 billion) was launched in the Earth’s orbit in April 1991-four centuries after his discovery. This telescope will look into the past and the origin of the Universe.

**John Kepler (A.D. 1571-1630)**

He was born at Germany in 1571. His main field of interest was professionally mathematics. He believed that all the natural laws could be expressed in terms of existing mathematics. He introduced three laws, known as Kepler’s Laws of Planetary Motion.

**Laws of Planetary Motion**

The planets move round the Sun in elliptical orbits with Sun as one of this focci.

The radius vector joining the planet and the sun sweeps equal areas in equal times.

The square of the periodic times of the various planets (including the Earth) are proportional to the cubes of the semi-major axis of their respective orbits.

These laws constitute the starting point of modern astronomy.

He also made a considerable contribution in the field of optics.

**Albert Einstein (A.D. 1879-1955).**

**He was born in Germany in 1879. He had Jewish origin. His fundamental intrestet were laws of physics and mathematics. He specially contributed the theory of relativity in physical sciences.**

The laws of nature are the same for all bodies in uniform motions.

It Says That:

(i) It is impossible to find out if two events happened at the same time.

(ii) All motion is relative.

Clock in motion slow down.

Iii An object in motion gets shorter in the direction of the motion.

Iv An object in motion has its mass increased because of the motion

The Special Theory covers only uniform motion, whereas the General Theory includes accelerated and rational motion as well.