John Dalton was an English chemist, meteorologist and physicist who was best known for his work in the development of modern atomic theory, and his research into colour blindness. In the early 1800s John Dalton proposed his atomic theory which operated under the following assumptions:1. All matter consists of tiny particles.

2. Atoms are indestructible and unchangeable.Atoms of an element cannot be created, destroyed, broken into smaller parts or transformed into atoms of another element. Dalton based this hypothesis on the law of conservation of mass and on centuries of experimental evidence

3. Elements are characterized by the mass of their atoms.All atoms of the same element have identical weights, Dalton asserted. Atoms of different elements have different weights.

4. When elements react, their atoms combine in simple, whole-number ratios.This postulate suggested a practical strategy for determining relative atomic weights from elemental percentages in compounds. Experimental atomic weights could then be used to explain the fixed mass percentages of elements in all compounds of those elements.

5. When elements react, their atoms sometimes combine in more than one simple, whole-number ratio.Dalton used this postulate to explain why the weight ratios of nitrogen to oxygen in various nitrogen oxides were themselves simple multiples of each other. Even Dalton's critics were impressed by the power and simplicity of his explanation, and it persuaded many of them that his atomic theory was worthy of further investigation.

However over time the Daltons atomic theory has been modified, as a result of the new discoveries in isotope y, nuclear fusion and fision, sub-atomic particles and polymerisation in organic compounds:

1. Atoms are indestructible and unchangeable.This statement only holds for ordinary reaction but during nuclear reaction atoms involved are disintegrated into smaller units with large release of heat energy and therefore the atoms are destroyed. The discovery of nuclear processes showed that it was even possible to transform atoms from one element into atoms of another.

2. Elements are characterized by the mass of their atomsWe now know that atoms of the same element sometimes have slightly different masses (with discovery of isotopy), but always have identical nuclear charge. In modern atomic theory, the postulate has been amended to read: "Elements are characterized by the nuclear charge of their atoms".

3. When elements react, their atoms combine in simple, whole-number ratiosThis theory can only apply for non-organic compounds which usually contain few atoms per molecule, but organic molecules undergo polymerisation and form giant molecules.eg starch and cellulose.

Science can be defined as the concerted human effort to understand, or to understand better, the history of the natural world and how the natural world works, with observable physical evidence as the basis of that understanding. It is done through observation of natural phenomena, and, or through experimentation that tries to simulate natural processes under controlled conditions. Since science seeks truth, it is constantly changing, revising and correcting itself to get closer to the truth. Consequently, the very nature of science is constant change, revision, upgrading, and self-correction. Science is in a state of ever-changing dynamism in order to obtain its goal of truth. The developments which lead to the modification of Daltons atomic theory is a good example of the ever changing nature of science. Aspects of the theory that were once accepted as a feasible truth in one era were challenged and disproven throughout a number instances over time and upgraded or new theories formed based on the results of recent, more updated experiments or the discovery of new information. This constant improvement and change represents the true nature of science.