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Millikan oil-drop experiment

First method for direct measurement of the electric charge of a single electron, originally performed in 1909 by Robert Millikan. He used a microscope to measure the rate of descent of tiny oil droplets directed through the top of a box. By halting the descent of droplets carrying their own electric charge by means of precisely adjusting the voltage between the box's metal top and bottom, he discovered that the electric charges on the drops were all whole-number multiples of a lowest value, the elementary electric charge itself, and thus that electric charge exists in basic natural units.

Learn more about Millikan oil-drop experiment with a free trial on Britannica.com.

Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.

Drag-and-drop

In computer graphical user interfaces, drag-and-drop is the action of (or support for the action of) clicking on a virtual object and dragging it to a different location or onto another virtual object. In general, it can be used to invoke many kinds of actions, or create various types of associations between two abstract objects.

As a feature, support for drag-and-drop is not found in all software, though it is sometimes a fast and easy-to-learn technique for users to perform tasks. However, the lack of affordances in drag-and-drop implementations means that it not always obvious that an item can be dragged.

Actions

The basic sequence involved in drag-and-drop is:

Press, and hold down, the button on the mouse or other pointing device, to "grab" the object,
"Drag" the object/cursor/pointing device to the desired location,
"Drop" the object by releasing the button.

Dragging requires more physical effort than moving the same pointing device without holding down any buttons. Because of this, a user cannot move as quickly and precisely while dragging (see Fitts' law). However, drag-and-drop operations have the advantage of thoughtfully chunking together two operands (the object to drag, and the drop location) into a single action . Extended dragging and dropping (as in graphic design) can stress the mousing hand.

A design problem appears when the same button selects and drags items. Imprecise movement can cause a dragging when the user just want to select.

Another problem is that the target of the dropping can be hidden under other objects. The user would have to stop the dragging, make both the source and the target visible and start again. This issue has been dealt with in Mac OS X with the introduction of Exposé.

In Mac OS

Drag-and-drop was used in the original Macintosh to manipulate files (for example, copying them between disks or folders. ). Mac OS has always had a system wide drag and drop. For most of its time, the OS has not updated the drag and drop.

In Mac OS , the user can install software without using the setup, the user can drag the contents of the disk and drag it to another drive to initialize the installation.

Another feature was dragging text or picture to any where were you can bypass the clipboard introduced in System 7.5.

The dragging of window contents was introduced in Mac OS X.

Mac OS X allows users who are dragging window contents, to return to it's position when the mouse is released.

In Windows

Jeffrey Greenberg claims that the first drag & drop implementation for Windows was his shareware program called Aporia in 1988 under Windows 2.0, and later commercialized as WinTools In Aporia/WinTools all icons had functions that could be obtained by double clicking the left mouse button, by clicking on the right mouse button, or by dragging onto one of several functional icons, such as printing, copying, viewing, and other actions. If an icon was double-clicked on and ran a program, the icon changed to indicate that a program was running, and if it was then dragged to the trash, the program was exited. (factoid: A defect in the implementation lead to a workaround of the Windows operating system Aporia Bits)

Subsequently numerous other competitors provided drag & drop desktop replacements to the standard Windows interface including the Norton Desktop, Xerox, NewWave, and Central Point. In Windows 95, Microsoft prevented developers from taking over the desktop and released a drag & drop model of their own.

In OS/2

The Workplace Shell of OS/2 uses dragging and dropping extensively with the secondary mouse button, leaving the primary one for selection and clicking. Its use like that of other advanced Common User Access features distinguished native OS/2 applications from platform-independent ports..

Examples

A common example is dragging an icon on a virtual desktop to a special trashcan icon to delete a file.

Further examples include:

Dragging a data file onto a program icon or special window for viewing or processing,
Moving or copying files to a new location/directory/folder,
Adding objects to a list of objects to be processed,
Rearranging widgets in a graphical user interface to customize their layout,
Dragging a command onto an object to which the command is to be applied,

e.g. dragging a color onto a graphical object to change its color,

Dragging a tool to a canvas location to apply the tool at that location,
Creating a hyperlink from one location or word to another location or document.
Most text editors Visual Studio, for example, allow dragging selected text from one point to another.