While mainland newspapers and radio scouts hunted in vain, to use their own expressions, for President Roosevelt, on Tuesday and Tuesday night, the Chief Executive was lying snugly and quietly aboard the Potomac, anchored in Tarpaulin Cove. The presence of the presidential yacht in the cove was known on the Vineyard in the early afternoon, but so far as is known no one attempted to approach the craft and certainly no one who knew of her presence there, tipped off any institution or individual that might have invaded her privacy.