# File lib/spreadsheet/workbook.rb, line 46
   def add_worksheet(name=nil)
      index = @worksheets.length

      if name.nil?
         name = SheetName + (index + 1).to_s
      end
      
      args = [name,index, @active_sheet, @first_sheet, @url_format]
      ws = Worksheet.new(*args)
      @worksheets[index] = ws
      return ws
   end