paint material made against one of similar nature and use and of known properties, will give on exposure to the weather more reliable information regarding the value of the new material than any other method now in common use. In this way it is possible to control carefully the variable factors always present in each painting job, such as condition of surfaces, character of paint, state of weather, and method of application, each of which has far-reaching effect on the durability of the paint coating.

Actual service tests under normal conditions give the most conclusive data to guide us, but so long as it takes years to make them, common sense dictates that consumers should hold fast to materials that universal experience has proven trustworthy, until better are found. Accelerated tests under  "abnormally  severe conditions"  have