Euclid has worked in many other areas of geometry such as in the book ‘Data’ where his plane geometry is mentioned. Another book ‘On Division’ also deals with Euclid’s ideas on plane geometry. ‘Phaenomena’ by Euclid would be the modern day ‘applied mathematics’ which concerns the geometry of spheres used mostly in astronomy. Other survived works include ‘Optics’ and ‘Porisms’. ‘Optics’ corrected the misconception of the time that the sun, moons and other heavenly bodies are the same size as they appear to the naked eye. Euclid did this by working out the relation between the eyes and the things seen by them. The work ‘Porisms’ is sometimes believed to be more advanced mathematics than the ‘Elements’. Porism is not like a theorem which is used to prove a theory but actually is used to highlight a feature of an already present theory.