EMANCIPATION DAY IN POUGHKEEPSIE. A large number of colored people assembled in Poughkeepsie on Monday, to celebrate the anniversary of British West Indian Emancipation. The leading feature of the day was an address by Fred. Douglass, which covered the entire ground presented in the question as to the effects of Emancipation, and reviewed the present government and its policy as affecting the growth of slavery. He was particularly severe on his namesake, the Senator from Illinois.