Served asset /application.css - 304 Not Modified

Hi
I am thinking to hide warning that is ”Served asset /application.css -
304 Not Modified”.
How can I fix something if I change the settings?
I've run that is less than

server:
rails new myapp
cd myapp
rake db:migrate
rails s

client:
http://localhost:3000/books

warning:
Started GET "/assets/books.css?body=1" for 127.0.0.1 at 2012-02-26
14:48:35 +0900
Served asset /books.css - 304 Not Modified (5ms)

Started GET "/assets/application.css?body=1" for 127.0.0.1 at
2012-02-26 14:48:35 +0900
Served asset /application.css - 304 Not Modified (4ms)

Started GET "/assets/scaffolds.css?body=1" for 127.0.0.1 at 2012-02-26
14:48:35 +0900
Served asset /scaffolds.css - 304 Not Modified (1ms)

Started GET "/assets/books.js?body=1" for 127.0.0.1 at 2012-02-26
14:48:35 +0900
Served asset /books.js - 304 Not Modified (1ms)

Started GET "/assets/application.js?body=1" for 127.0.0.1 at
2012-02-26 14:48:35 +0900
Served asset /application.js - 304 Not Modified (4ms)

Started GET "/assets/jquery_ujs.js?body=1" for 127.0.0.1 at 2012-02-26
14:48:35 +0900
Served asset /jquery_ujs.js - 304 Not Modified (2ms)

Started GET "/assets/jquery.js?body=1" for 127.0.0.1 at 2012-02-26
14:48:35 +0900
Served asset /jquery.js - 304 Not Modified (2ms)