20. To what societies Act applies.-- The following societies may be registered under this Act:- Charitable societies, the military orphan funds or societies established at the several presidencies of India, societies established for the promotion of science, literature, or the fine arts, for instruction, the diffusion of useful knowledge, 2 [ the diffusion of political education] the foundation or maintenance of libraries or reading- rooms for general use among the members or open to the public, or public museums and galleries of paintings and other work of art, collections of natural history, mechanical and philosophical inventions, instruments, or designs.