Referencing a cell on another worksheet

Hi all, I know there is a simple way to reference a cell on another worksheet - but can it be done by formula?

In sheet 1 and sheet 2 of the attached workbook I have data in column A.

In sheet 3 I want to reference a specific cell in each sheet. I know I can manually type =Sheet1!A7 into cell H3 of sheet3, but can I use a formula to use the Sheet name and cell reference to do this (the cell reference may change from time to time)