Why is the second image always the brightest while the others are of diminishing brightness when there is a formation of multiple images in a thick plane glass plate or thick mirror?

When an object is observed through a thick mirror, silvered at its back, a large number of images are obtained. Out of all the images, the second image is the brightest. In this case, the first image is formed by reflection at the first surface, which is the unsilvered surface of the mirror. The second image is formed after reflection from rear silvered surface, which sends maximum amount of light. Rest of the images formed are due to internal multiple reflections which occur inside the mirror. These images contain lesser amount of light and so their intensity gradually decreases.