The radiator used as the standard on these tests was an ordinary cast-iron two-column steam radiator, 38 inches high, with but little ornamentation. The writer believes that this is the only way of accurately testing radiators, and the adoption of any one definite make of radiator as a universal standard of comparison would do much to extend the knowledge of the comparative effect and value of radiators. Tests of radiators made in different ways or in different locations are valueless for accurate comparison. But all comparative tests made against the same standard if accurately and carefully carried out, could be compared in percentages of the heating effect of the standard used. The writer found that under the conditions in his testing plant the 38-inch two-column cast-iron radiator used as a standard gave out 1.60 British thermal units per square foot per hour per degree difference of temperature with an average steam temperature of 224 degrees Fahr., and average temperatures of the rooms of 76.5 degrees. The average difference of temperatures was 147.5 degrees.
This cofficient of 1.6 B. T. U. per square foot per hour per degree difference of temperature between the steam and air is somewhat lower than that which Prof. Carpenter obtained for a radiator of almost the same size and design. Assuming that the radiators were exactly alike, such variation as there was can be due to two causes: 1, a variation in the difference of temperature between the steam and the surrounding room; and 2, the mode of setting and the consequent freedom of air circulation around the radiator. In regard to the first cause, all tests of radiating surfaces from Péclet down show that the coefficient is greater, the greater the difference of temperature, and for extreme variations in the difference of temperature, the coefficient is very much greater than in the limits of ordinary radiator practice, with steam temperatures from 212 to 230 and mean air temperatures from 40 to 70; within which range the variation in the coefficient from this cause is less than 9 per cent. In regard to the second cause—the freedom of the air-circulation around the radiator—this is by far the chief cause of difference in action of radiators. Profs. Denton and Jacobus of the Stevens Institute of Technology made some comparative tests of radiators, published in The Engineering Record of September 8, 1894, with a plant very similar to that used by the author, except, besides having an opening at the top, there was in each of the test rooms an outside win-
