An interesting aside is the investigation of the Water clock in the tower of winds in Athens
http://www.jstor.org/pss/503828
Carnatic Chronology - the Hindu and Mahomedan methods of reckoning time explained by Charles Philip Brown - 1863
http://books.google.co.in/books?lr=&id=w5MAAAAAMAAJ&dq=feroz+shah+observatory&q=observatory#search