RELATION BETWEEN THE ELECTROMOTIVE FORCE OF A DANIELL

CELL AND THE STRENGTH OF THE ZINC SULPHATE SOLUTION.

By Prof. H. S. CARHART, N. W. University, Evanston, Ill.

[ABSTRACT.']

THIS investigation was carried out in the physical laboratory of the university in Berlin. The electromotive force was measured by the compensation method of Poggendorff. The two poles of the battery A to be measured are connected with two points on a second circuit containing a battery B of higher electromotive force than A. The resistance between the points is then varied till no current flows through the circuit of battery A. The difference of potential between the two points common to the two circuits is then equal to the electromotive force to be measured. By Ohm's law the product of the resistance between the two points and the current flowing through the main circuit equals the electromotive force of the battery A.

The current was measured by a silver voltameter with pure nitrate of silver. The resistance employed was in Siemens' units. The deposition of silver in a silver cup was continued ten minutes with a current of slightly over one-tenth of an ampère. The cup was then washed with great care, dried in a hot-air chamber, and weighed after cooling, fractions of milligrams being obtained by taking the swing of the pointer.

The cell to be measured consisted of a U tube, the bend being much smaller than the two branches, the form being that employed by Kohlrausch in measuring the resistance of electrolytes. The lower portion of the tube was first filled with a saturated solution of zinc sulphate; copper sulphate was then added to one branch and a percentage solution of zinc sulphate to the other, the surface of separation between the two adjacent solutions being sharp in each case. No perceptible diffusion of the solutions took place during the time required for the measurement of the current.

The following condensed table exhibits the results:

1 Printed in full in Am. Jour. Sci., Nov., 1884.

SENSITIVENESS Of photographic DRY PLATES. By Wм. H. PICKERING, Mass. Inst. of Technology, Boston, Mass.

[ABSTRACT.]

THE object of this research was to determine the sensitiveness of the various kinds of dry-plates on an absolute scale, and to state it in terms of the sensitiveness of pure silver chloride. The chloride is first exposed in a box one meter in length having an aperture 15.8 cm. in diameter at one end. It is exposed under a graduated scale of tissue paper to the light from the blue sky in the zenith, for a definite time, say eight minutes. The plates to be tested are then cut up in narrow strips, and exposed under the scale to a smaller aperture (.05 cm. in diameter) for a shorter

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."

HENRY A. HAZEN, O. C. S. O., Washington, D. C.

[ABSTRACT.1]

By Prof.

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