The difference between discovery and invention is to find first what has been already in existence; as discovery of America in 16th century and the invention is finding what is new, unseen, unheard of; may be imagined or needed to meet some purpose. Sometime it comes accidently, as x-ray. While researching for something else, passing electro wave through a vacuum tube, it emerged. Luckily the table where the experiment was on, in the drawer of the same table some photographic plates was...