<div class="section abstract"><div class="htmlview paragraph">MR. KELLEY discusses the application of the automatic transmission to passenger cars, buses, cross-country military vehicles, off-the-highway equipment, and trucks, placing particular emphasis on the development of satisfactory units for the truck field.</div><div class="htmlview paragraph">Today, he says, there is a strongly crystallized trend among engineers toward the use of only two engineering principles for handling the variable drive ratios in automatic transmissions. These are the Hydra-matic and the hydrodynamic principles.</div></div>