1. J. J. Thompson

2. J.J. Thompson aka Joseph John
Earlier days

3. General information
He is credited for the discovery of the electron and of isotopes
He was credited with the invention of the mass spectrometer.
Thomson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron and for his work on the conduction of electricity in gases.

4. Start of Thompson’s contributions
Until the end of the nineteenth century, the accepted model of the atom resembled a billiard ball.
In 1897, J. J. Thomson dramatically changed the modern view of the atom with his discovery of the electron.
Thomson's work suggested that the atom was not an "indivisible" particle as John Dalton had suggested but, a jigsaw puzzle made of smaller pieces.

5. Cathode Ray
Thompson knew that opposite charges attract and like charges repel
He hypothesized that a cathode ray is a stream of tiny negatively charged particles moving at high speed
He called the particles corpuscles.
They were later called electrons.

6. He set up an experiment to measure the ration of the charge of an electron to its mass.
The ratio was constant
In addition, the charge to mass ratio of electrons did not depend on the kind of gas in the cathode ray tube or the type of metal used for the electrodes.
He concluded that electrons must be parts of the atoms of all elements

7. Thomson did more experiments on the cathode tube. 
He placed two electric plates on its path. 
One was positively charged. 
The other was negatively charged. 
The glowing  light bent towards the positively charged plate.and found that the glowing  materials  bent towards the positively charged plate.
He found out that the glowing light were smaller particles. 
They were smaller than the atom. Thus J.J.Thomson's atomic theory was found.

9. Mass spectrometer

10. Plum pudding model
Electrons are imbedded in a sphere of positive electrical charge.
In looked like raisins stuck in dough
This model was short lived due to the groundbreaking work of Ernest Rutherford, a student of Thompson