Abstract Studies to determine the laws of behavior of stack gases as they flow downwind, and to prevent down-wash of these gases, have been in progress at the University of Michigan since March, 1934, when a project (1, 2) in this field was sponsored by the Commonwealth Edison Company of Chicago under the direction of Mr. William L. Abbott and Mr. Alex D. Bailey. That pioneer project was connected with the Crawford Avenue Station and was followed during the later years by other studies dealing with the extension of old plants and the design of stacks for new plants. The material presented in this paper was obtained almost entirely from recent studies sponsored by the Commonwealth Edison Company.