Spreadsheet gem


Here is a newbie question on the spreadsheet gem.

I have the following simple test code in a controller action :

    require "spreadsheet"

    @csd = cns_period_conv(params[:date][:year],params[:period_start])
    book = Spreadsheet::Workbook.new
    sheet1 = book.create_worksheet #default sheet name Worksheet1
    sheet1.name = 'My First Worksheet'
    sheet2 = book.create_worksheet :name => 'My Second Worksheet'
    sheet1.row(0).concat %w{Name Country Acknowlegement}
    sheet1[1,0] = 'Japan' #get the Cell at row 1, column 0
    sheet1.row(0).height = 40
    format_1 = Spreadsheet::Format.new :rotation=> 90, :vertical_align => :center, :horizontal_align=>:center
    sheet1.row(0).set_format(0, format_1);
    sheet1.row(2).push 'One','Two','Three'

    sheet1.column(2).width = "Acknoledgements".length
    format_2 = Spreadsheet::Format.new :horizontal_align=> :center
    sheet1.row(0).set_format(2, format_2);

    book.write 'Excel.xls'

I would like to open this file in Excel instead of saving it to the harddisk. What have I missed?

Best regards,