time, say 30 seconds. The last degrees of the scale as printed on the chloride, and photographed on the plates, are then noted and the relative amount of light received in the two cases compared, thus giving the absolute sensitiveness of the plates in terms of the sensitiveness of the chloride. The observations were repeated using gas-light as a source of illumination, and it was found that those plates most sensitive to daylight were in several cases the least so to gaslight. PHOTOGRAPHY OF THE INFRA-RED REGION OF THE SPECTRUM. By WM. H. PICKERING, Mass. Inst. of Technology, Boston, Mass. [ABSTRACT.] IN the investigation described below, ordinary gelatine dry plates were employed. It was soon found, however, that some kinds were much more suitable for this purpose than others. Walker Reid and Inglis, and Allen and Rowell plates, being those which gave the best results. With an ordinary spectroscope, with one flint glass prism, there is no difficulty, by concentrating the light, in photographing as far below A, as A is below D on the prismatic spectrum, or to w. 1. 11300. In order to do this one. need only place two pieces of red glass before the slit and give a sufficient exposure. It is well to paint the back of the plate black, to avoid the halo produced by the brighter portions of the spectrum. By using a four inch prism, and camera lens, the latter of about twelve inches focus, one may reach a wave length of 13800 in about ten minutes. By using a wide slit of about 15' angular aperture the A line may be photographed in about a third of a second, and a few seconds more is sufficient to cause the spectrum in the neighborhood of the C line to reverse and become nearly transparent. THUNDERSTORMS AND THEIR RELATIONS TO "LOW." By Prof. HENRY A. HAZEN, O. C. S. O., Washington, D. C. [ABSTRACT.1] PROF. TAIT'S views as to the origin of atmospheric electricity. The work of Palmieri in Italy and of Bezold in Bavaria; especially 1 Presented by permission of the Chief Signal Officer of the Army. in determining the general distribution of thunderstorms on any day and the laws governing their origin, development and progress. The great advantage this country offers for such study. The special investigations begun in January of this year and continued to the present time. Results. A study of the storms of May 17-20 leads to the following conclusions: 1. Hail falls occurred, with relatively low pressure at a storm centre, in the region to the southeast of "LOW "and at distances of about 250 miles. 2. Thunderstorms were also mostly in the same region but at distances, on the average, of 450 miles. In cases where these occurred to the west and northwest of "LOW," they were sporadic and of little intensity. 3. In this region the winds were gentle and southerly. 4. In many instances there was a furious gust of wind from the west immediately preceding the storm, an increase of eight and ten times the previous velocity in a few minutes. 5. In a few cases where the barometer was frequently read it was found to indicate a rather sudden increase in pressure as the storm came up. 6. The intensity was greatly diminished at nightfall and again increased the day following. 7. The velocity at which the storms travelled from west to east, spreading somewhat in a fan shape, was, on May 19, from 10 a. M. to 3 P. M., 37 miles per hour; from 3 P. M. to 10 P. M., 38 miles per hour, while the velocity of" LOW" was 23 and 10 miles per hour, respectively. This seems to show that the relation, if there be one, is with the general disturbance rather than with its centre and that the forces which determine the formation and progress of thunderstorms are in a manner independent of those acting in the "LOW" itself. Is this greater velocity of thunderstorms than of "LOW," due to their distance from the centre and a consequent greater circumferential motion? NOTES ON ACOUSTICS. By Prof. CHAS. R. CROSS, Mass. Institute of Technology, Boston, Mass. [ABSTRACT.] I. Quality of sound as related to Change of Phase. When an induction coil is used in telephony there is of course a difference of phase of a quarter of a wave-length between the electrical undulation in the primary and that in the secondary circuit owing to the action of the induction coil. Hence, if any complex musical sound is transmitted by such an apparatus there is a great change in the phase-relations among the partial-tones of the note. If the quality were to be noticeably altered by such a change there should be a perceptible difference in quality between the sound heard in two receiving telephones, one in the primary and the other in the secondary circuit of an induction coil connected up in the ordinary manner with a microphone or other transmitter. No differences of this kind have been perceived either with the tones of such musical instruments I have transmitted, or with the voice. By suitably adjusting the resistance of the two telephone receivers even the loudness of the sounds heard in the two circuits can be made identical. There is no perceptible change of phase from self-induction in the simple circuit described. II. Remarks on a Point in Helmholtz's Theory of Consonance and Dissonance. Helmholtz considers beats to be due to an interference of vibrations in the vibrating parts of the inner ear, and assumes that no two sounds can produce beats unless the interval between them is so small that they both affect the same vibrating part of the inner ear. In addition to Koenig's experimental disproof of the supposition that notes cease to beat when their interval is considerable, the view of Helmholtz as to the physiological action in the ear is in opposition to certain undoubted facts of audition. Beats may occur either between a sound and the after sensation of a previous sound, and, still more, between two sounds acting only upon opposite ears. The latter fact I have confirmed by observing the beats between mistuned unisons and other mistuned intervals given by two tuning-forks; one acting directly upon one ear, and the other transmitted by telephone to the other ear. The beating with the after sensation shows that unless the after-sensation itself is due to persistence in vibration of the vibrating parts (which is certainly not the fact) the discussion of Helmholtz is in complete. This view is still further confirmed by the production of beats from the excitation of separate ears. There must be a deeper action than that considered by Helmholtz, a kind of interference in the sensorium itself instead of, or rather, in addition to, the interference of vibrations in the inner ear. III. Intensity of Sound as related to Amplitude of Vibration. In the ordinary statement that the intensity of sound is proportioned to the square of the amplitude of vibration, a proposition that has of late been clearly recognized as applying in any case only to sounds of the same pitch, the complexity of the relation between the intensity of the vibration exciting the ear, and the resulting sensation has been universally lost sight of. Probably, though not certainly, the Psychophysic Law of Fechner applies to intensity-variations, and the sensation certainly does not increase as rapidly as the exciting cause. Hence, in strictness, we cannot assume the ordinary statement to be accurately true except in applying it to objective sound. It is a mechanical rather than an aural measure of the intensity, that we assume. Also in the diminution of intensity with increase of distance, the sensation must diminish less rapidly than the law of inverse squares would lead us to suppose. IV. On a Musical Application of the Principle of Fatigue. In the so-called "Voix celeste " stop in cabinet organs a tremolo is produced by calling into play two sets of reeds just out of unison with each other, which make slow beats with each other and with the notes produced on other stops in use at the same time. Besides this, there is a remarkable strengthening of the whole body of tone from the instrument. This seems to arise from the increased average intensity of the sensation due to the alternate increase and decrease of sound, which, however, with the slow beats used, is not so great as to become harsh and painful. ON A PROPOSED METHOD FOR ASCERTAINING THE LEAST NUMBER of THE methods hitherto used for this purpose are all of them defective for the reason that the vibrations produced are complex in their nature instead of being pendular. In the method proposed pendular vibrations are employed. Two magnetic-telephones are connected up with each other in the usual manner, and a circuitmaking wheel with a single radial metallic strip is interposed, so that by the rotation of the wheel the circuit shall remain closed for a short interval, which can be determined by the rapidity of rotation. If the sound of a tuning-fork giving pendular vibrations is transmitted through the circuit a greater or less number of these vibrations, or even a fractional part of a single one, can be caused to act upon the ear. Suitable precautions are taken to avoid the production of extraneous sounds in the circuit itself. A properly adjusted microphone transmitter with an induction coil may be substituted for the magneto-transmitter, the circuit-making wheel being placed in the secondary circuit. UPON A GENERATOR IN USE AT CORNELL UNIVERSITY FOR PRODU CING OXYGEN AND HYDROGEN GAS BY MEANS OF THE DYNAMO MACHINE. By Prof. Wм. A. ANTHONY, Cornell University, [ABSTRACT.] THE generator which forms the subject of this paper has now been in use for more than three years at the Cornell University with such good results that it is deemed worth while to give some account of it. The generator consists of twelve cells, each cell being essentially a U tube of white earthen ware with suitable openings for introducing the electrodes and for replenishing the fluid. The electrodes are of platinum foil 24 × 5 inches, attached to the ends of lead tubes which serve at the same time for conveying the current and delivering the gas. The openings are stopped by paraffined corks, and the tubes from the several cells are connected to the general delivery tubes (of lead) in the same way. twelve cells are connected electrically in series. The In an experiment to determine the maximum amount of gas to be obtained by the power at command (about 5 H. P.) the result was as follows: Amount of both gases evolved in three hours 544.8 litres, or .00226 grms. per cell per second. This would correspond to 24.49 |