Excerpt from Photometry of the Gas-Filled Lamp As the filament has a positive temperature-resistance coefficient, the resistance decreases and consequently the current increases at constant voltage. At high values of voltage the mean temperature of the gas is higher than at low voltage, consequently the tempera ture of the filament is reduced in a lesser degree by rotation and the change in current, though positive, is less at high than at low voltage. On the other hand, when the lamp is rotated at high speeds the cooler gas at the bottom of the bulb is thrown out by centrifugal force, which varies as the square of the speed, and the hot gas tends to remain near the center, thus considerably retarding the convection currents which cool the filament. The result is an increase in the resistance of the filament as a whole and a decrease in the value of the current. At high voltages the mean tempera ture of the gas is higher than at low voltage and the retarding efiect due to centrifugal force is decreased; hence the change in current due to rotation is less than at low voltages. At low speeds, as seen above, the temperature of the filament is lowered and consequently the candlepower is decreased. At high speeds the temperature of the filament is raised, and hence there is an increase in the candlepower. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.