New to the boards, so please be gentle.

I'm after some information about a postcard I have.
More specifically what time period it came from and what sort of value.
It is unused and dates from what i believe is the early 19th century, but stand to be corrected.
On the back it says:
"The X-Ray Illusion Postcard"
Published by WH Smith & Sons 186 the Strand
On the front is an x-ray picture of a hand with a metal like disc/washer in middle of hand and a small hole, on side of picture it says patent applied for
under picture it says:
"RAYONS X STRAHLEN RAYS"
With instructions:
"To see the bones in your hand place the hole of the card to your eye and your hand with fingers apart 12 inches distance in front of a window".
thank you in anticipation