Automatic Change of Internet Connection

I normally have my desktop connected to the internet via ethernet. However, I occasionally need to disconnect the cable and move over to wifi. I click on the little 'globe' and select the wifi icon. When the cable is plugged back in I have to deselect the wifi the same way. This is no hardship. However, I was wondering if there is a way of automatically changing to and from wifi depending on the connectivity of the ethernet cable. I've searched the settings, but can find no help.

Thanks.

I'm a little confused by the instructions in the link given. In Option 1, the ethernet and wifi values from the screenshot are 5 and 35 respectively - mine are 35 and 70 respectively. The instructions put in a value equal to current value. Also, it's not clear if a higher or lower value would cause the wifi/ethernet to pull out if the other is operational. Would lowering the wifi interface metric value below 35 (or raising the value of the ethernet above 70) be the correct thing to do?

Also, when I plugged the ethernet cable back in, I noticed that the connection symbol in the systray changed from wifi to ethernet. Does this mean that it's doing what I want, anyway, or in the wifi still active?

Thanks.