Option d is the correct answer. Sawai Jai Singh II, Maharaja of Amber and Jaipur, constructed five observatories in the second quarter of the eighteenth century in the north Indian cities of Shahjahanabad (Delhi), Jaipur, Ujjain, Mathura, and Varanasi. Important Tips Jantar Mantar: "Jantar Mantar" means "instruments for measuring the harmony of the heavens". The primary purpose of the observatory was to compile astronomical tables, and to predict the times and movements of the sun, moon and planets. The Ram Yantra, the Samrat Yantra, the Jai Prakash Yantra and the Misra Yantra, etc are the distinct instruments of Jantar Mantar. Among these five observatories, Delhi observatories was the first to be built.