Doors and Windows - Repairing glass pane in an old french door

I need to repair a pane of glass in an old French door. The house was built in 1925 and I think the door is original.

The problem is there doesn't seem to be any room to install a new piece of glass. There's no glazing or caulking around the pane and the channel that the glass sits in doesn't look to be very deep. But I'm sure something is holding it in place...I just can't figure out what.

When I buy a new pane of glass, how do I measure the correct size? Then how do I install it?

The panes in a door are held in place by strips of wood.

This link shows how to replace window glass, door glass is covered at the bottom.

http://www.nrha.org/orgill/How-To/doors_win/glass/broken.htm

Measure the glass opening exactly and tell the vendor it is an exact opening so it can be cut the right size, generally 1/16" to 1/8" under, depending upon the overall size. You might take a piece of the old glass with you to try to get the same thickness if possible.

Hope this helps.

Thanks so much for the information. I have printed the instructions from the link you mentioned....it was really helpful.

Wish me luck!!