PHILOSOPHICAL SOCIETY OF WASHINGTON

The 802d meeting was held at the Cosmos Club, March 2, 1918. Vice-President HUMPHREYS in the chair; 40 persons present. The minutes of the 801st meeting were read in abstract and approved.

Lieut. D. L. WEBSTER presented a paper on Emission quanta phenomena in X-rays, illustrated by lantern slides. The paper was a brief account of the work on this subject that has appeared in the past three years in the Physical Review and the Proceedings of the National Academy of Sciences.

In the general radiation spectrum, the frequency whose quantum is the energy of one cathode electron was found by Duane and Hunt, and by Hull, to have an upper limit, at which the spectrum ends. It was shown by Webster that the existence of such a limit to the spectrum is direct evidence that the rays are trains of periodic waves rather than pulses; and with further experimental work, that if atoms in the anticathode could be struck only by electrons of a definite velocity, any atom's chance of emitting rays of a given frequency jumps from zero discontinuously to a finite value as the energy of the cathode electron is raised continuously past the quantum value of that frequency. A further continuous increase of energy of the cathode electron would produce a continuous decrease of intensity of rays of that frequency.

For the characteristic rays of the K series, it was found by Webster that no such rays are produced until the cathode electron's energy reaches the quantum value of the highest frequency of the series, at which point all the lines of the series appear together. Their intensities increase by the same law for all lines, but this law is very different from that holding for any given frequency in the general radiation. These phenomena are all consistent with the hypothesis that the primary characteristic rays produced by cathode rays come from the same atomic mechanism as the secondary characteristic rays occurring in fluorescence. This statement holds, whatever that mechanism may be.

For the L series it was found by Webster and Clark that the laws are similar to those of the K series except that the lines must be considered as belonging to at least two, and probably three, separate series, each of which behaves like the K series.

Discussion: This paper was discussed by Messrs. SWANN, WHITE, and FOOTE.

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The second paper, on Determination of the constant C2 of Plan k's law, was presented by Major C. E. MENDENHALL. It was illustrated by lantern slides. No abstract furnished. A paper of the same title was published in the Physical Review, 15:515. November, 1917.

Discussion: This paper was discussed by Messrs. CRITTENDEN, ABBOTT, COBLENTZ, FOOTE, SOSMAN, WHITE, SWANN, and WEBSTER. H. L. CURTIS, Recording Secretary.

The 803d meeting was held at the Cosmos Club, March 16, 1918. President BURGESS in the chair; 39 persons present. The minutes of the 802d meeting were read in abstract and approved.

A paper on Thermal expansion of alpha and of beta brass by P. D. MERICA and L. W. SCHAD was presented by Mr. Merica. This paper was illustrated by lantern slides. Within the past four years an investigation has been in progress at the Bureau of Standards of the cracking or fracturing of cast and wrought brass, particularly of the type composition, 60 per cent of copper and 40 per cent of zinc. It has been found that in most failures of such brasses in service the cracking can be ascribed to the presence of initial stresses in conjunction with surface corrosion. These initial stresses may be produced either in the mechanical working of the material, such as drawing or rolling or by shrinkage, as in the case of cast metal. As, however, a number of instances of cracking in brass of this type have come to the attention of the authors for which such explanations cannot be applicable, it was their intention to ascertain whether local internal stresses could not be produced in brass of this composition by heat treatment such as it might receive in manufacture.

Brasses of this type are heterogeneous, consisting of the mechanical mixture of two constituents, called respectively, the alpha and the beta constituents. Measurements of the linear thermal expansion of these two constituents have shown that of the beta constitutent to be considerably in excess of that of the alpha. So great is this difference that rough calculations have shown the possibility of the development of average stresses due to the sudden cooling by quenching of the brass containing these constituents equal to approximately 15,000 pounds per square inch.

Experiments showed that these stresses were probably responsible for the lowering of the proportional limit of such brasses amounting to as much as 25 per cent.

The thermal expansion curves illustrate also very well the nature of the thermal transformations in the beta constituent varying about 1460°C.

Discussion: This paper was discussed by Messrs. WHITE, BRIGGS, and BURGESS.

A paper on The principles of electrical measurements at radio frequencies was presented by Mr. J. H. DELLINGER. The principles of radio or high-frequency measurements are coextensive with the principles of radio engineering to an extent not true in other fields. This is typified in the wavemeter, which is a complete radio transmitting and receiving station, albeit in miniature. The principles of ordinary alternating current theory apply with little change to the phenomena at very high frequencies. This was not true a few years ago, when damped waves were universally used in radio work, but the introduction of satisfactory sources of undamped currents has largely eliminated the specialized theory that went with damped waves.

While precision measurements with direct current are commonly made by null methods, high-frequency measurements on the other hand use the opposite critical phenomenon, a maximum rather than minimum of current. Resonance or tuning is thus the basis of radio measurements as well as of wave transmission and reception. At resonance the reactances due to capacity and to inductance annul each other and the current is limited by resistance only. As resistances are small in comparison with reactances at radio frequencies, the current is relatively very great at resonance, i.e., the resonance is very sharp and is thus a suitable basis for measurements.

The wavemeter is a resonance instrument, and is used to measure capacity and inductance as well as wave length. The other most generally useful radio instrument is the ammeter. With these two, measurements are made of current, resistance, power, and associated quantities, in addition to the quantities above mentioned. In general the best methods are those which are the least complicated. This is particularly true because of the disturbing effects of small inductances and capacities in lead wires and accessory apparatus. Small capacities in and near the measuring circuits are especially troublesome. They include the capacities of instrument cases, table tops, walls, and the observer, and they cannot always be determined or eliminated.

While resistance is of distinctly less importance in determining the flow of currents at high frequencies than at low, nevertheless resistance is the measure of power consumption. As it varies rapidly with ratio frequencies, its measurement is very necessary. The same measurement gives resistance and the associated quantities, sharpness of resonance, phase difference, and decrement.

Great advances in the precision of all these measurements have recently been made possible by the introduction of electron tubes as sources of current. They have the very great advantage of giving a steady current, and as the current is undamped the simple sine wave theory of alternating currents may be used.

Discussion: The paper was discussed by Messrs. WHITE, BICHOWSKY, and SWANN.

Mr. G. W. VINAL then gave a paper on Some electrical properties of silver sulphide. Silver sulphide may be prepared in the form of short wires or thin strips like a metal. The wire, which must be drawn hot, has been found to conduct electricity like a metal of high specific resistance and practically zero temperature coefficient. The strip of sulphide, rolled at room temperature, has a large temperature coefficient and shows both metallic and electrolytic conduction at the same time. It has a volt-ampere curve characteristic of a pyroelectric conductor. The resistance of these strips has been examined with both alternating and direct current, with the result that the alternatingcurrent resistance was nearly always found to be higher than that with the direct current, and the passage of a small alternating current of a frequency as low as 60 cycles increased temporarily the resistance of the sulphide, while a small direct current produced the opposite effect.

Experiments were made to find the electrochemical decomposition due to the electrolytic conduction of the strips of sulphide. A strip in air (5.5 by 0.3 by 0.01 cm.) with silver-plated ends was soldered to copper leads and put in a direct-current circuit. The initial current of 25 milliamperes was passed through it for nearly an hour without visible change. The current was increased by steps of 50 milliamperes at 10-minute intervals until with 200 milliamperes a discoloration of the plating at the anode end was noticed. A further increase to 300 milliamperes completed the destruction of the silver plating at the anode end and finally burned off the terminal, but before this happened a myriad of little shiny silver crystals appeared on the black surface of the sulphide. The appearance of these crystals was carefully studied under the microscope, and it was found that they occurred even to within a small fraction of a millimeter of the anode terminal. They appeared in various forms, some of which suggested that they had been expelled from the interior of the sulphide by considerable force.

Discussion: The paper was discussed by Messrs. BUCKINGHAM, HONAMAN, BICHOWSKY, SOSMAN, and BURGESS.

E. C. CRITTENDEN, Corresponding Secretary.

BOTANICAL SOCIETY OF WASHINGTON

The 128th regular meeting of the Society was held at the Cosmos Club at 8.00 p.m., Tuesday, April 2, 1918. There were 28 members and 4 guests present. Messrs. L. L. C. KRIEGER, H. F. BERGMAN, G. A. MECKSTROTH, and WM. N. ANKENEY were elected to membership. The following scientific program was given:

CARLETON R. BALL: The grain sorghums: a botanical grouping of varieties cultivated in the United States (with lantern). There are two chief centers of origin for the sorghums, Africa and India. The principal groups cultivated in the United States are kafir, milo (including feterita), and durra. All of these are of African origin. The kafir varieties mostly were obtained from the native tribes in Natal, South Africa. The Guinea kafir, however, probably was derived from the West Coast of Africa, whence it was brought as food for slaves during their long voyage to America. It is now cultivated in several islands of the West Indies. The milo varieties probably are of Egyptian origin. Very similar forms are grown in Egypt today under the names Durra Beda (white), Durra Safra (yellow), and Durra Ahmar (brown). Feterita was derived from the British Egyptian Sudan. The durra varieties, white and brown, probably came from North Africa, where they are still found among the native tribes. These are the varieties known in California as "White Egyptian corn" and "Brown Egyptian corn," respectively. The white variety has been grown in the Great Plains area under the name "Jerusalem corn." The kaoliang varieties are derived from North China and Manchuria. The different groups are clearly separated by botanical characters. The speaker exhibited charts showing by means of keys the classification of the sorghums.

The chief groups of the sorghums are Broomcorn, Sorgo, Kaoliang, Kafir, Shallu, Durra, and Milo. Keys were given showing the relation of the varieties of the Kafir group and of the Durra-Milo group.

F. V. RAND: The Shaw aquatic gardens (with lantern). The Shaw Aquatic Gardens, near Washington, were started several years ago as a matter of curiosity and recreation. Beginning with a half-dozen roots of the native white waterlily set in a little dug-out pond in the swamps of the Anacostia River the gardens have increased in size until there are over five acres under water. In these ponds are grown nearly all varieties of water plants that will live in our climate. They are sold all over the United States and even in the Hawaiian Islands. The business has been an artistic and financial success from the start; but has not been without its difficulties. Turtles, muskrats, and various insects offer each their special brand of tribulation. The biology and successful control of a serious fungus disease of pond lilies (caused by Helicosporium nymphaearum n. sp.) have been worked out by the writer; and a fungous leaf spot of Egyptian lotus (caused by an Alternaria) is under study.

Following Mr. Rand's paper, Mrs. FOWLER, the Manager of the Shaw Gardens, invited the members of the Society to visit the gardens and pointed out that June is one of the best times to inspect them. H. N. VINALL, Corresponding Secretary.

BIOLOGICAL SOCIETY OF WASHINGTON

. The 581st regular meeting of the Society was held in the Assembly Hall of the Cosmos Club, Saturday, March 9, 1918; called to order at 8 p.m. by President ROSE; 30 persons present.

On recommendation of the Council Miss E. E. STEVENSON was elected to membership.

Two informal communications were presented:

T. S. PALMER made remarks on the systematic feeding of quail in the city of Washington during the past winter. A census of these birds showed 60 coveys with a total of 1235 individuals. Discussed by Gen. T. E. WILCOX.

R. W. SHUFELDT showed lantern slide X-ray picture of the doubleheaded tortoise exhibited at the previous meeting of the Society. Major Shufeldt also exhibited two living specimens of the whip-tailed scorpion, Thelyphonus giganteus, collected by Mr. Nelson R. Wood, at Auburndale, Florida. Reference was made to its geographic distribution, Florida and West Indies, its habits in capitivity, its structure, and its systematic position. Its popular names were stated to be vinegerone, vinaigner, mulekiller, and vinegar maker.

The regular program consisted of three communications:

JOHN T. ZIMMER: An intensive feeding habit in young herons. Read by the Recording Secretary in the author's absence in New Guinea. This note will appear in full in the Proceedings of the Society. It was discussed by Dr. T. S. PALMER and ALEX. WETMORE.