firstPage.onmouseover = stopScrolling;
firstPage.onmouseout = scrollPages;

and similarly for the second page:

secondPage.onmouseover = stopScrolling;
secondPage.onmouseout = scrollPages;

The onmouseover event occurs when the mouse is placed over the scroll box. The onmouseout event occurs when the mouse is removed from the scroll box area. The event handler for the onmouseover event is the scrollPages() function. It starts the pages going, just as the invocation of the program does in the first place:

function scrollPages() {
    Gtimer = setInterval("moveUp()", Ginterval)
}

The Gtimer variable stores a pointer to the setInterval() command, which invokes the moveUp() function every Ginterval milliseconds. The event handler of the onmouseout event is the stopScrolling() function which clears the Gtimer pointer and thus cancels the call to the moveUp() function, causing the pages to halt:

function stopScrolling() {
  clearInterval(Gtimer);
}

Learn more about our scroller in Column 32, Scrolling HTML Basics, Part III: The Cross-Browser Version.

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