A Treatise on Industrial Photometry with Special Application to Electric Lighting

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1894 Excerpt: ... the burner; the horizontal distance from the center of the flame to the screen is 1.5 inches (38.10 mm.). The height of the flame from the burner is 3 inches (76.2 mm.) for carburetted gas; these two heights of the flame are defined by a double set of horizontal wires forming sights fixed on the screen. The chimney of the Argand burner is 2 inches (50.8 mm.) in diameter and 6 inches (152.4 mm.) in length. The Methven standard, being very simple in construction, is not subject to derangement, and its use is extremely easy. When employing ordinary gas, it is much better than the candle in au open-air photometer. The indications of the Methven screen with carburetted gas are very concordant. Thus Dibdin, in a very extensive investigation of the different light standards, found, out of 283 experiments, 211 or 74 per cent, in which the results did not differ by 1 per cent from the mean. The Giroud burners and the Methven screen may render marked service as intermediate standards, always on the condition of having their values determined in comparison with the absolute standard. By supplying these burners with gas stored in the gas-holder of the laboratory at the commencement of the experiment, we have at our disposal a source of light which remains constant for many hours, and whose employment requires no delicate manipulation. This is of considerable advantage, and makes these burners, notably that of Giroud, valuable auxiliaries in photometric researches. Vernon-Harcourt's Pentane Standard. 97. The objections which may be made to photometric standards in which ordinary illuminating gas is employed, evidently cease if we are able to have gas of constant composition. It is this constancy of composition which Methven sought to realize, in a certain measure, by r...