Even geniuses can suffer from alzheimers, schizophrenia, personality disorders, delusions, etc. just like the rest of us. Sure there's the stereotypical eccentric genius, but if someone starts making wild unproven claims coupled with increasingly strange behavior, that doesn't seem exactly like something a genius would do. That sounds like a very intelligent person suffering from mental illness. From wikipedia:

>At the 1932 occasion, Tesla claimed he had invented a motor that would run on cosmic rays.[205] In 1933, at age 77, Tesla told reporters that, after thirty-five years of work, he was on the verge of producing proof of a new form of energy. He claimed it was a theory of energy that was “violently opposed” to Einsteinian physics, and could be tapped with an apparatus that would be cheap to run and last 500 years. He also told reporters he was working on a way to transmit individualized private radio wavelengths, working on breakthroughs in metallurgy, and developing a way to photograph the retina to record thought.

We know that cosmic rays aren't prevalent enough to produce energy. It should be obvious that you can't record thought through a retina because the majority of thought in the brain occurs in areas obstructed by the retina. He was just an already-eccentric old man whose brain was breaking down, and in trying to cling onto his success from the past he might have developed delusions that to him seem perfectly logical. I don't see why we can't accept that the death ray idea was just as nonexistent/nonsensical as these other ones. Additionally, also from wikipedia:

>In a box purported to contain a part of Tesla's "death ray", Trump found a 45-year-old multidecade resistance box.