visible?

Returns true if the variable is public.

tobj = WIN32OLE_TYPE.new('Microsoft Excel 9.0 Object Library', 'XlSheetType')
variables = tobj.variables
variables.each do |variable|
  puts "#{variable.name} #{variable.visible?}"
end

The result of above script is following:
  xlChart true
  xlDialogSheet true
  xlExcel4IntlMacroSheet true
  xlExcel4MacroSheet true
  xlWorksheet true