Thanks to our buddy Bill Rabel in Seattle for the impetus to write this article. After Mark Anbinder wrote in "Call Me 'Two Finger' Mark" (2007-05-21) about how he was surprised to find himself addicted to two-finger scrolling on his MacBook (which is equivalent to using a scroll wheel or Mighty Mouse scroll ball), Bill went spelunking and found a trick I hadn't previously known, causing me to look for other scroll wheel tips. (And if you're interested in the history of the scroll wheel, check out "The Evolution of Scrolling: Reinventing the Wheel," 2004-12-13.)
Scroll Horizontally -- Many applications, such as word processors, are oriented vertically, so scrolling up and down with the scroll wheel is intuitive. But what about applications like Microsoft Excel and ProVUE Development's Panorama database, which often require scrolling horizontally? Just hold down the Shift key and your scroll wheel switches to controlling the horizontal scroll bar instead of the vertical scroll bar. Applications must support this Mac OS X feature explicitly, so it may not be universal to all applications with a horizontal scroll bar.
Zoom In, Zoom Out -- Hold down the Control key while you scroll with the scroll wheel and Mac OS X 10.4.8 or later will zoom the screen smoothly. Mac OS X has long provided screen zooming (see the Universal Access preference pane), but it required keyboard shortcuts that were awkward and jerky. Screen zooming isn't just for those who have trouble reading too-small text or for presenters who want to focus on a particular part of the screen, though; it's also great for zooming tiny Internet videos up to full-screen size. Of course, they pixelate more at larger sizes, but that's fine if you're sitting further back from the screen anyway. The only downside is that it's hard to get the mouse pointer out of the picture when you're zoomed in on a video; normally you want the pointer to stay in the zoomed screen.
A further tip: if you take a selection screenshot with Command-Shift-4 or Snapz Pro X while zoomed in, the screenshot reflects your zoom level properly (trying to take a screenshot of an entire window while zoomed doesn't work, though).
Scroll to Switch Applications -- I'm not sure if this is any easier or not, but if you press Command-Tab, let up on the Tab key, and then use your scroll wheel, Mac OS X will scroll the selection in the application switcher. Of course, you can also just keep pressing Tab, which seems easier, or hover the mouse pointer over an application's icon to select it.
Per-Frame Advance in QuickTime Player and iMovie HD 6 -- Want to see if animators hid secret messages in individual frames of a film? If you can open it in QuickTime Player, using the scroll wheel pauses playback and then either advances or rewinds a frame at a time. It's probably a little easier to do with a real scroll wheel that has little detents as you scroll. Alas, this trick doesn't work in iTunes, DVD Player, or VLC, though you can play .m4v files from the iTunes Store in QuickTime Player.
The same trick works in iMovie HD 6, too, but with a caveat. The scrolling seems to work only as a per-frame preview; if you press the left or right arrow keys, which also rewind or advance per frame, the video jumps back to the point where you started scrolling.
Tab History Navigation in Mozilla-based Browsers -- Here's the tip Bill found. If you use Firefox or Camino with tabbed browsing, hold down the Option key and turn the scroll wheel to scroll backward and forward in the tab's history. These browsers navigate back or forward one page for every scroll detent. It's a fast way to move back through a lot of pages in a tab, though it's easy to overshoot your target. Oddly, Netscape and Mozilla use Shift as the modifier key to navigate through a tab's history, and Safari and OmniWeb don't have the feature at all.
Change Font Size in Firefox and Camino -- It's all too common to run across a Web page with text that's too small to read (Geoff Duncan explained this in "Why Windows Web Pages Have Tiny Text," 1999-02-15). All Web browsers make it easy to expand or shrink text, usually with Command-+ and Command--, but you can also use the scroll wheel to do this in Firefox and Camino. Just hold down Command-Control and scroll to adjust text size.
Slow Down Text Scrolling in Firefox -- Normally, if you're scrolling through a long Web page, the speed accelerates as you turn the wheel. That's good, since it means you can get to the bottom of a page quickly if you want. But at times you might want a slower scrolling speed so you don't accidentally scroll past where you're reading. Hold down the Command key while scrolling in Firefox and scrolling will slow to what seems to be an almost fixed rate. It might be useful if you prefer to keep your eyes in one spot on the page and scroll the text past that spot.
Zoom In and Out in Word and Excel -- Speaking of small text... In Microsoft Word and Excel, if you find yourself squinting to read text at the default font size, you can zoom in and out with the scroll wheel. In Word, hold down Command-Control and scroll to change the zoom level by 10 percent increments per detent. In Excel, hold down Control-Option to zoom in and out by 15 percent increments. If you're using two-finger scrolling on a trackpad, zooming in and out in this fashion may be hard to control.
Control Time with iCal -- In iCal's Day and Week view, you normally see the hours from 8 AM to 6 PM, or whatever you've set in iCal's General preference pane. But by holding down Option and rolling your scroll wheel, you can increase or decrease the number of hours that appear in Day or Week views without opening the preferences window. Note that the changes are persistent, but they aren't reflected in the preferences window.
Scroll Through the Years in iPhoto -- In iPhoto 6's Calendar pane, Apple gave us funny little up and down arrows on either side of the pane's title for scrolling through the years. An easier way to scroll forward and backward in time in that pane is to use the scroll wheel - just make sure the mouse pointer is over that portion of the screen first.
There is one notable place where the scroll wheel doesn't match up to dragging the scroller in the scroll bar. In iPhoto 6, when you scroll by dragging the scroller, iPhoto pops up a translucent display containing the name and date of the current film roll, updating it smoothly as you drag. Alas, that doesn't work if you scroll with a scroll wheel, so here's hoping that iPhoto 7 rectifies that situation.