An apparatus to experimentally verify the accuracy of filmwise condensation heat transfer theories for small diameter horizontal tubes was developed. The apparatus was designed so that the condensation pattern was visible at all locations, all of the parameters necessary to calculate the average heat transfer coefficient were accurately determinable, and the removal of noncondensible gases was effected before the start of the condensation process. A method was devised to insulate the test specimen and cooling water from the rest of the apparatus to obtain an accurate measure of the heat transfer rate. The surface temperature of the tubes was directly measured by copper-nickel thermocouples which were electroplated onto the tube. Initial testing of the apparatus was performed using steam as the condensing vapor. Difficulty in obtaining and maintaining filmwise condensation was caused by small amounts of impurities which were introduced during the assembly of the apparatus. The surface thermocoup]es produced output of approximately l mv per 75 F and were responsive to transient temperature fluctuations. / Master of Science