Authorities in Indian capital Delhi unsuccessfully carried out a cloud seeding trial, which is the science of altering clouds to make rains, to tackle the city's worsening air pollution on Tuesday. Cloud seeding is done by firing small particles - usually silver iodide - into clouds to produce rain. The technique is used around the world, but experts doubt its efficacy as a long-term air pollution control measure. A team of the Indian Institute of Technology (IIT) Kanpur and the Delhi