Take a circular glass slab, and mark something on a curved side, now see the image of the mark from opposite side of the slab. I observed that it is magnified, why is it so?
In this, only one refraction is taking place, on the observer side.
Using ray diagrams I tried to form the image. Image formed is real and forming outside the slab, but I don't observe the image outside the slab. It just appears to be magnified.
I have added an image, may be it will clarify what I am trying to ask.
it is very difficult to localize a picture, your eye adjusts to the rim of your slab an your brain beliefs the image there. When you know, where the image should be, you can put a little frame there or something else, your eye can adjust to, and you will see the image in the calculate distance, or you take small bulb from a flashlight, instead of you mark and see the real image on a piece of paper.
You are imagining that the image is formed inside the sphere but a real image is formed outside the glass sphere on the side remote from you marked point.
You can use the method of no-parallax to identify the position of the real image as described in this answer.
Leeuewenhoek, a Dutchman 1632 - 1723, made the first practical microscopes using small glass spheres as the objectives and here is a photograph taken of diatoms using one of his microscopes with a magnification of 300x.
To achieve such an image the objective produced a real image with is further magnified by an eyepiece. Your glass sphere will also produce a real image but not that it might be fairly distorted.
