Swami Vivekananda, late in the year l895 wrote in a letter to an English friend, "Mr. Tesla thinks he can demonstrate mathematically that force and matter are reducible to potential energy. I am to go and see him next week to get this new mathematical demonstration. In that case the Vedantic cosmoloqy will be placed on the surest of foundations. I am working a good deal now upon the cosmology and eschatology of the Vedanta. I clearly see their perfect union with modern science, and the elucidation of the one will be followed by that of the other."
Here Swamiji uses the terms force and matter for the Sanskrit terms Prana and Akasha. Tesla used the Sanskrit terms and apparently understood them as energy and mass. (In Swamiji's day, as in many dictionaries published in the first half of the present century, force and energy were not alwavys clearly differentiated. Energy is a more proper translation of the Sanskrit term Prana.)
Tesla apparently failed in his effort to show the identity of mass and energy. Apparently he understood that when speed increases, mass must decrease. He seems to have thought that mass might be "converted" to energy and vice versa, rather than that they were identical in some way, as is pointed out in Einstein's equations. At any rate, Swamiji seems to have sensed where the difficulty lay in joining the maps of European science and Advaita Vedanta and set Tesla to solve the problem. It is apparently in the hope that Tesla would succeed in this that Swamiji says "In that case the Vedantic cosmology will be placed on the surest of foundations." Unfortunately Tesla failed and the solution did not come till ten years later, in a paper by Albert Einstein. But by then Swamiji was gone and the connecting of the maps was delayed.