(FORTUNE Magazine) – Okay, you've finally come to terms with the implausible fact that engineers can squeeze a million transistors onto a silicon chip the size of your thumbnail. But are you ready for really eensy machines -- including silicon grippers, generators, and electric motors -- no bigger than the dot on this letter i? Applications could range from tweezing a single cell to powering tiny drills through the plaque in your arteries. A chip is just a mini-road map for electrons, while one of these new gadgets is a whole shrunken city. Work on these mind-boggling micromachines has been under way for several years, but scientists in academe and at companies including Ford, Toshiba, and Toyota are now combining minuscule motors and other tiny parts into working systems. The difficulties are as vast as the machines are small. To help solve them, the American Society of Mechanical Engineers and the Institute of Electrical and Electronics Engineers launched in March the Journal of Microelectromechanical Systems. Smallness has inherent advantages, says editor William Trimmer: ''An ant can carry many times its weight not because it's so much stronger than we are, but because the scaling of the laws of nature makes small things relatively stronger and faster.'' Many of the microdevices being developed are sensors to detect movement, say, or light, or changes in chemical composition. They will be not only smaller but probably cheaper, less power-hungry, more accurate, and more reliable than their macro counterparts. By 1993 cars could be using a deceleration detector made by Analog Devices of Norwood, Massachusetts, to set off an air bag (photo at left). Analog Devices' sensor will cost less than $10 and replace from four to six larger detectors that cost more than $15 each. Richard S. Muller, a Berkeley professor, says the product points to what is possible: ''We want to give computers the means to interact with the real world -- using equivalents to hands, a nose, ears, and eyes.'' To expand what microdevices can do, this summer scientists at the University of Wisconsin expect to complete a working system using nickel, aluminum, and silver parts assembled on a silicon base. It will include a motor, gearbox, and control unit connected to a generator. Air or hydraulic pressure might drive a future generator powering a microsensor in some inaccessible place -- deep inside a fluid-filled pipe or even an artery. The whole assembly would fit into a square a fifth of an inch on a side.