Mostly scientist comes to the conclusion when they repeat their work again and again. They first gather data from authentic sources, made experiments and then before jump into conclusion made several hit and trial. After getting the successful results by implementing the same strategy, they provide a conclusion of the specific scientific theory.
In general it was the "slum dwellers" and the "immigrants" who did not share in the prosperity of the late 1800s, since these people were paid very low wages and treated poorly.
