rails3 ruby1.9.2

■
I get 'Routing Error' when I post something on form from
indexhtml to show.html

※Controller

class AlertsController < ApplicationController

def index
end

def show
@name = params[:name]
end

end

※View

alerts/index.html
<% form_tag :action => 'show' do %>
<%= text_field_tag("name") %>
<%= submit_tag "Send" %>
<% end %>

alerts/show.html
<%= @name %>