Explain how the understanding of atomic emission spectrum lead to development of the atomic theory

here we have to explain the development of the atomic theory by the atomic emission spectrum.

The most important aid in determining the structure of an atom has been study of radiation emitted and absorbed by the elements. The glowing atoms of an element emit radiations.

These are called the atomic spectra. This study helped to understand the structure of the atoms.

To explain the atomic spectra the Bohr's model was introduced. The postulates of the Bohr's model explain the fine spectrum of the atom up to the particle nature of the electrons.

Later some modification on the Bohr's postulates was made to explain the wave nature of the electrons as well. But the atomic spectra is best be understood by the Bohr's atomic model which developed the atomic theory.

Thus the understanding of emission spectrum of atom to develop the atomic theory is explained.  

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)