ways. Certain bright line spectra of glowing vapors, the composition of whose light is really altogether different from the continuous spectrum of the sun, may have the power of stimulating the three primary sensations of red, green, and violet in nearly the same proportions; and thus, as in the case of CO2 in vacuum tubes under certain conditions, may be made to simulate sunlight in some respects. All known solids, at temperatures of incandescence attainable in practice, are, however, relatively much stronger in red and weaker in the violet than daylight. Candles, oil and gas flames; the Nernst filament and mantle burner; glow-lamps, whether with filaments of carbon, tantalum or tungsten, are all intermediate as regards the distribution of intensities in their visible spectra between the Hefner standard lamp and the acetylene flame. How small a range of variation they cover as regards quality of light, and how different they are from daylight, may be seen from Fig. 11, in which the spectrophotometric curves for the Hefner lamp and the acetylene flame are drawn.11 In this diagram, ordinates are values for each wave-length of the ratios. Hefner/daylight or acetylene/daylight. The brightness of the spectra is so chosen for ease of comparison that these ratios are unity in the yellow region (0.590μ). The standard for daylight used in this comparison is from the average of numerous measurements taken in all sorts of weather, during what I have since learned from European meteorologists was an abnormally dull or gray season. Had the observations been confined to the sort of day which one would naturally select on which to sample daylight, the contrast with these artificial sources would have been much more striking. Now, while we cannot increase the degree of incandescence of these sources of low temperature so as to make them approach appreciably nearer to sunlight, it is possible to change the quality of their light by the use of properly selected color screens, and this is the second of the two possible methods to which reference is made above. When we try the experiment by placing over half of the field of the lantern a blue screen which gives a fair match as "Nichols: "Daylight and Artificial Light," Transactions of the Illuminating Engineering Society, 1908 (May). to color with daylight, and, by means of a carefully-chosen amber screen, reduce the other half to the color of candle-light, we get, as you see, by direct appeal to the senses, a telling realization of the significance of these curves in Fig. 11, and we have brought home to us the very great difference between the light of the heavens and that by which the greater part of our indoor work is done. Fortunately the preponderance of the longer wave-lengths in artificial light is one which is restful rather than harmful The distribution of intensities in the spectra of the Hefner lamp and the acetylene flame compared with daylight. to the eye (which bears excess of violet and ultra-violet so ill), and it is doubtless more healthful to work under a ruddy illumination of fifty candle-meters than to strain the eyes with the two or three candle-meters of cold daylight, which, according to recent measurements, 12 is all that reach the pages of readers in the rooms of many public libraries. 12 66 'Nature," 88, p. 600, an abstract of L. Weber's recent Study of Daylight in Schriften des Naturwissenschaftlichen Vereins für Schleswig-Holstein, xv, i. TELEGRAPHY FOR FIELD LINES OF INFOR- BY GEORGE O. SQUIER, Ph.D., Major, Signal Corps, U. S. A. THE Signal Corps of the army at present uses for the service of the mobile forces radio-communication for cavalry operations, and insulated field wire laid on the ground and operated by "buzzers" for infantry and mixed commands. Pure radio-communication is ideal for rapidly moving troops, but has the inherent defect that interference is always possible, and that information may under certain conditions be received by the enemy. Radio methods and field wire methods have, however, taken their places as permanent means of electrical intercommunication in war. At present, the apparatus and the operation of these two methods are distinct and separate. The subject of this paper pertains to some preliminary experiments involving a useful combination of these two methods for field service. It should be distinctly understood that it is not proposed to do away with either pure radio-communication for field service, or the ordinary "buzzer" operation of wires, which latter has for so many years shown its great reliability in the field. It is rather proposed to supplement these methods by a combination of the two, which, under certain conditions of field service, it is believed will offer cardinal advantages. At the headquarters of a division or field army there will always be under the Chief Signal Officer a wireless equipment and also several wire lines radiating out from headquarters to the units of the command. So far as these headquarters are concerned, therefore, we have at present the full equipment required for operating "wired-wireless" telegraphy for military purposes. APPLICATION OF PORTABLE QUENCHED SPARK SET TO STANDARD SIGNAL CORPS FIELD WIRE. The standard Signal Corps field wire at present furnished consists of II strands of steel and one strand of copper, with *See "Electrical Methods of Intercommunication for Military Purposes," by George O. Squier, Ph.D., JOURNAL FRANKLIN INSTITUTE, 172, 545. a weight of about 70 pounds per mile and a resistance of about II ohms per mile. It is well known that electric waves are not transmitted as efficiently over iron wires as they are over copper wires. The greater the conductivity of the wire conductor, the less the line losses and hence the less the attenuation of the electric waves guided thereby. In addition, it is well known that in all experiments with high-frequency electric waves, where tuning to resonance is used, it is desirable that no iron should be employed. The results given below for field wire are, therefore, inferior to what would be obtained with copper conductors. The latest apparatus of the Signal Corps for wireless sets employs a 500-cycle generator developed for use on aëroplanes and "pack" sets, with a specially designed transformer and a quenched spark gap as distinguishing features. In the first experiments, the 500-cycle generator was driven by a direct-connected motor which was operated from power taken from a socket connection to a 110-volt electric lighting circuit. The generator delivers power at 110 volts with an output of about 125 watts. The spark gap was of the regular Signal Corps type, consisting of built-up discs of copper, separated by layers of mica ring insulation, and was practically noiseless in operation. The coupling employed was inductive in type and variable within wide limits, permitting the voltage and the current impressed upon the line to be controlled at will. Convenient tuning elements were available for insertion in the line at the transmitting end. With this arrangement the general efficiency of transmission of electric waves along the ordinary type of field wire described above was observed, the actual wave-length being about 400 meters as measured by a wave meter. The line wire was laid out in the ordinary manner upon the ground, and extended from the Signal Corps laboratory at the Bureau of Standards to improvised stations in the field at the end thereof. At the receiving end the regular wireless detector and high-resistance head-telephones were used. ELECTRIC WAVE TRANSMISSION OVER OPEN CIRCUIT LINE. Simple experiments showed that with a transmitting current of a few milliamperes loud signals were easily heard at the receiving end, using the "perikon" detector supplied in the field pack sets, without the necessity of any tuning either at the trans |