In 1876, Naoroji gave a series of lectures for the Bombay Branch of the East India Association, which he published as a pamphlet in 1878. These lectures were an early form of the "drain theory" argument, which he would expand in the more extensive version of the argument presented in 1901 as Poverty and Un-British Rule in India.
The lectures that formed the first version of the work, The Poverty of India, are notable in part because they were written just at the onset of the Great Madras Famine of 1876-1878. Many of the economic factors that contributed to the famine are described by Naoroji.
An extract from The Poverty of India can be found here.