He travelled across the kingdom and developed the first rainfall map of Travancore; in conjunction with this study, he published his first research paper: "On Thunderstorms over Trivandrum.

"[4] In late 1921, Ramanathan moved to Calcutta to collaborate with C. V. Raman, who had accepted him as a doctoral student, on studies of X-ray diffraction in liquids.

During the university holidays, he continued to carry out post-doctoral research under Raman's guidance, and in 1923 observed an unusual "fluorescence" in a beam of light when it was diffracted in water - which Raman eventually concluded was an effect caused by the substance, associated with a change in frequency equal to the molecular vibrational frequency.

[4] Appointed Superintending Meteorologist of the Poona Observatory during the Second World War, he assisted in training meteorological personnel for the Indian Air Force as it rapidly expanded during the wartime years.

[5] Having reached the statutory retirement age of 55 in 1948, Ramanathan left the Indian Meteorological Department that year and joined the newly established Physical Research Laboratory (PRL), Ahmedabad as its first director.

[4] Ramanathan retired in 1966 but continued to serve PRL as Emeritus Professor until his death on New Year's Eve 1984 at the age of 91.