Why does nose drops after gear up?

[Bolelas]

At first glance it seems wrong. But i read some article about a device (prototipe) to counteract this efect. So, it probably means this happens. (and i am not including flaps in it, this was second question)

"It is known that aircraft in flight, when lowering retractable landing gears in preparation for landing, experience a nose up condition."

I got it from here:http://www.google.com/patents/US3045954

It is the other way around, but samething. Thx for you answer Mr Freddie.