Sometimes discoveries are made unexpectedly matter of chance. This is serendipidity. Examples -
1. Structural formula of benzene - It was dreamt by Kekule. He got the idea of this ring like structure after seeing a snake licking its tail forming a ring like shape.
2. Principle of floatation - Discovered by Archimedes.
3. Law of graitation - Newton saw an apple falling on ground & got idea of law of gravitation.
4. Discovery of Pencillin - Alexander Flemming (1928) discovered antibiotic penicillin from Penicillium notatum.
5. Steam engine - James watt got the idea of utilising steam energy.
6. Anaphylaxin - Charls Ricket discovered it or allergic reactions by chance through second injection of poison into doges who had survived the first one.
7. Mutation - Sudden appearance of ancon sheep which had extremely small legs in a herd of normal sheep led to the discovery of mutation.