XXXVII. An Apparatus to show, simultaneously to several hearers, the Blending of the Sensations of Interrupted Tones. By ALFRED M. MAYER, Ph.D.* N the March number of this Journal, of the current year, I described several forms of apparatus used in my observations on the frequency of the interruptions of simple sounds required to blend these sounds and obtain from them continuous and uniform sonorous sensations. These experiments gave the data for the law connecting the pitch of a sound with the duration of its residual sensation. The various apparatus described in that paper are, however, unsuited to exhibit the phenomena to more than one hearer at a time. To enable many hearers to observe the phenomena simultaneously, I have devised the apparatus shown in the figure. D BS R A F A brass tube, T, of 1.25 centim. interior diameter and 1.8 centim. long, is cemented in a hole in the bottom of the glass * Communicated by the Author. flask A; which is a common form of flask, used by chemists. When the tube T is closed the air in the flask resounds powerfully to the sound of an UT, fork, F; but when this tube is open, the resonator resounds so feebly as to be just audible at the distance of several feet from the flask. If the tube be closed and opened several times in a second, we shall have loud explosions with faint interposed sounds. The opening and closing of the tube is effected by a perforated disk, D, revolving on a rotator, R. The tube T is placed in the circular path of the 16 holes which perforate the disk, with the mouth of the tube quite close to the surface of the disk. A short tube B, with flanges on it, slides neatly over the tube T, and the flange of B is pressed against the surface of the disk D by the helical spring S. By this arrangement the tube T is fully opened when a hole in the disk coincides with the opening of the tube, and is entirely closed when the flange of B is between the holes in the disk and gently pressing against its surface. On slowly rotating the disk, while the fork is kept in vibration by an electromagnet, we have the perception of powerful beats which become more and more frequent as the velocity of rotation of the disk is increased till, with a certain velocity, the beats blend into a smooth continuous sound, which is that given by the fork when held near its proper resonator. This sound of UT, as given by the blending of its interrupted sounds is, however, accompanied by another and graver sound; but the existence of this additional sound does not interfere with the clear perception of the blending of the interrupted sounds of UT3. With this apparatus the blending of interrupted sounds has been shown to the entire satisfaction of a large audience. To enable one readily to make the apparatus, the following dimensions are given. The diameter of opening of mouth of flask is 3 centim. Depth of flask, 16.25 centim. Capacity of flask, including tube T, 483 cubic centim. In the figure the rotator, R, is shown driven by a cord. It is necessary, if an accurate determination is to be made of the duration of the residual sensation, to drive the disk by gearing as is done in the apparatus I have used. When the disk is driven by a cord one can show the blending of the interrupted sounds, but an accurate determination of the duration of the residual sensation is prevented by the friction which exists between the flange of B and the disk, though these surfaces are coated with a film of oil. XXXVIII. Notices respecting New Books. THE MEAN DENSITY OF THE EARTH: an Essay to which the Adams Prize was adjudged in 1893 in the University of Cambridge. By J. H. POYNTING, Sc.D., F.R.S. (Charles Griffin and Company.) THE HE study of this work of Professor Poynting will be of the utmost value not only to anyone who proposes to engage on the special subject with which it deals, viz., the combined mathematical and experimental determination of the constant of gravitation-but also to the fairly large class of investigators who, in other experimental researches, have to deal with the measurement of extremely small quantities and with the action of disturbing influences both small and great. The chief value, indeed, of the Essay consists in the help which it affords in anticipating and allowing for such disturbances, and in the fairly complete historical résumé of the work which has been done, with the same object, by previous investigators. A work of this kind would lose much of its value if it did not contain a fair record of failures as well as of successes; and the author has not omitted to point out the defects which experiment from time to time revealed in his originally projected methodsas, for example, when in 1888, after he had supposed that the work was finished, he was led to suspect the existence of a tilting of the whole floor of the room in which his balance was placed by the moving of the large attracting mass from one position to another; an unfortunate circumstance which necessitated the employment of a second attracting mass whose action was such as to diminish the effects which were to be observed. The author is to be congratulated on the strictly scientific title under which he describes his work-"The Determination of the Mean Density of the Earth," or "The Determination of the Constant of Gravitation," instead of the utterly unmeaning "Determination of the Weight of the Earth," which is found in even such a work as Arago's 'Popular Astronomy,' and which is a characteristic of too much of our modern popular science à la mode. Have we not seen in some old and popular treatise a picture of "the room in which Mr. Baily weighed the Earth"? It is to be hoped that some day our leading authorities will be induced to abandon that fatal dogma which is still, unfortunately, "of great emolument "that Science, to be popular, must, above all things, be inaccurate. We have said above that the chief value of the work consists in its helpfulness and suggestiveness, although it is tolerably certain that, with all the precautions which the author has taken to ensure success, the value which he has found for the mean density (viz. 5.493) must be very near the truth. He himself points out (p. 107) that with all apparatus the greater the size the greater are the errors produced by air-currents, a fact of which he was unaware when his apparatus was designed; and that, if he were to start with a new design, he would certainly make the whole arrangement on a smaller scale-a great change which was advocated and justified by Professor Boys in a preliminary paper on the Cavendish experiment, read before the Royal Society in May 1889. There XXXIX. Proceedings of Learned Societies. GEOLOGICAL SOCIETY. [Continued from vol. xxxvi. p. 594.] November 22nd, 1893.-W. H. Hudleston, Esq., M.A., F.R.S., President, in the Chair. THE following communications were read : : THE In previous communications the author has maintained that the different masses of eruptive rock which occur within the sunken tract of country lying between Lake Mjösen and the Langesundsfjord are genetically connected, and have succeeded each other in a regular order. The oldest rocks are the most basic, the youngest (except the unimportant dykes of diabase) are the most acid, and between the two extremes he has found a continuous series. He is now preparing a detailed monograph on this series of eruptive rocks, and in the present communication he gives an account of the results of his work on the oldest members. Several bosses of basic plutonic rock, now forming a series of dome-shaped hills, lie along a north-and-south fissure-line. The most northerly is that of Brandberget in the parish of Gran, about 50 or 60 kilometres N.N.W. of Christiania, and the most southerly occurs at Dignaes on Lake Tyrifjord, about 35 kilom. W.N.W. of the same town. The prevailing rock in these bosses is a medium or coarse-grained olivine-gabbro-diabase; but pyroxenites, hornblendites, camptonites, labrador-porphyrites, and augite-diorites also occur. Analyses of the typical rocks from three localities on the north-and-south line are given, and the conclusion is reached that the average basicity of the rocks forming different bosses decreases from north to south. The contact-metamorphism is referred to; and the presence of hypersthene in the altered Ogygia-shales, coupled with its absence from the same shales where they have been affected by quartzsyenite, leads the author to the conclusion that the chemical nature of the intrusive rock does, in certain cases, produce an influence on the character of the metamorphism. Innumerable dykes and sheets of camptonite and bostonite are associated with the above-mentioned plutonic bosses. These are regarded by the author as having been produced by differentiation from a magma having the composition of the average olivine-gabbrodiabase. Analyses are given, and it is proved that a mixture of nine parts of the average camptonite and two of the average bostonite would produce a magma having the composition of the average olivine-gabbro-diabase. The petrographical variations, such as the occurrence of pyroxenites and augite-diorites, in the plutonic masses themselves are described, and attributed to differentiation under |