Thanks to this invention, he was able to take photos of scenes with little light. He was able to capture the struggles of the poor and shed light on the difficulties they faced on a daily basis. He first began showing his work as lantern slides in lectures presented for entertainment. However, he also published his work in a book called How the Other Half Lives. The book was published in 1890 and became an international sensation. His writings, combined with his photographs, bear strong witness to society's indifference towards the poor. As an advocate for the poor, the oppressed and the exploited, Riis wrote about how they were victims of economic slavery. His writings brought shock and horror to New York's upper and middle class. It also caught the attention of Theodore Roosevelt. After Roosevelt became governor, he closed the poorhouses and passed many reforms that helped combat poverty in the slums. Roosevelt called Riis "New Zealand's most useful citizen ».