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Observations, &c. (continued).
Museum of Practical Geology. Catalogue of the Library, compiled by H. White and T. W. Newton. 8vo. 1878.
The Museum. Madrid - Observatorio de Marina de San Fernando. Almanaque Nautico para 1879. 8vo. 1878.
The Observatory. Naples :-Zoologische Station zu Neapel. Mittleilungen. Band I. Heft 1. 8vo. Leipzig 1878.
Dr. Dohrn. Washington (U.S.]:-Geological and Geographical Survey of the
Territories. Bulletin. Vol. IV. No. 2, 3. 8vo. 1878. Miscel. laneous Publications. No. 10. 8vo. 1878. Geological and Geographical Atlas of Colorado and portions of adjacent territory, by F. V. Hayden. folio. 1877.
Dr. Hayden. Alvarenga (P. F. Da Costa) :-Leçons Cliniques sur les Maladies
do Cour, traduit du Portugais par E. Bertherand. 8vo. Lisbonne 1878.
Ansted (D. T.), F.R.S. Water and Water Supply, chiefly in reference to the British Islands. Surface Waters. 8vo. London 1878.
The Author. Beke’s (Dr. Charles) Discoveries of Sinai in Arabia and of Midian, edited by his Widow. 8vo. London 1878.
Mrs. Beke. Fitzgerald (R. D.) Australian Orchids. Part 4. folio. Sydney.
The Author. Fournié (Édouard). Application des Sciences à la Médecine. 8vo. Paris 1878.
The Author. Gore (G.), F.R.S. The Art of Scientific Discovery, or the general
conditions and methods of Research in Physics and Chemistry. 8vo. London 1878.
The Author. Kingzett (C. T.) Animal Chemistry, or the relations of Chemistry to
Physiology and Pathology. 8vo. London 1878. The Author. Lenhossek (Joseph de). Des Déformations Artificielles du Crane. 4to. Budapest 1878.
The Author. Markham (Clements R.), F R.S. A Memoir on the Indian Surveys. Second edition. roy. 8vo. London 1878.
The Author. Miers (John) F.R.S. On the Apocynaceæ of South America, with some preliminary remarks on the whole family. 4to. London 1878.
The Author. Miller (J.) Metaphysics, or the Science of Perception. 8vo. New York 1875.
The Author. Munk (W.) The Roll of the Royal College of Physicians of London. Second edition. 3 vols. 8vo. London 1878.
The College. Odling (Mrs.) Memoir of the late Alfred Smee, F.R.S., by his Daughter. 8vo. London, 1878.
The Author. VOL. XXVIII.
Prusol (Joshua). Dreams of my Solitude on the Life and Mechanism of the Heavens and their hosts. 8vo. Edinburgh 1878.
The Author. Ramsay (A. C.), F.R.S. The Physical Geology and Geography of
Great Britain. Fifth edition. 8vo. London 1878. The Author. Schwendler (Louis). Government Telegraphic Department. Instructions for testing Telegraph Lines. Vol. I. 8vo. London 1878.
The Author. Studnitz (A. von). Gold, or Legal Regulations for the Standard of
Gold and Silver Wares in different countries of the world, translated by Mrs. Brewer, with Notes and Additions by E. W. Streeter. 12mo. London 1877.
The Editor. Wigner (G. W.) The Water Supply of Sea-side Watering-places. 12mo. London 1878.
The Author. Winthrop (R. C.) Correspondence of Hartlib, Haak, Oldenburg, and
others of the founders of the Royal Society, with Governor Win, throp of Connecticut, 1661–1672. 8vo. Boston (U.S.) 1878.
The Editor. Wittstein (G. C.) The Organic Constituents of Plants and Vegetable
Substances, and their Chemical Analysis. Authorised translation by Ferd. von Mueller, F.R.S. 8vo. Melbourne 1878.
December 5, 1878.
W. SPOTTISWOODE, M.A., D.C.L., President, in the Chair.
The President announced that he had appointed as Vice-Presi. dents:
The Hon. Sir James Cockle (elected in 1865) and Lord Lindsay were admitted into the Society.
The Presents received were laid on the table, and thanks ordered for them.
The following Papers were read :
I. “On the Illumination of Lines of Molecular Pressure, and
the Trajectory of Molecules.” By WILLIAM CROOKES, F.R.S., V.P.C.S. Received November 30, 1878.
(Abstract.) Induction Spark through Rarefied Gases. Dark Space round the
round the negative pole of an ordinary vacuum tube when the spark from an induction coil is passed through it. He describes many experiments with different kinds of poles, a varying intensity of spark, and different gases, and arrives at the following propositions.
Illumination of Lines of Molecular Pressure. a. Setting up an intense molecular vibration in a disk of metal by electrical means excites a molecular disturbance which affects the surface of the disk and the surrounding gas. With a dense gas the disturbance extends a short distance only from the metal; but as rarefaction continues the layer of molecular disturbance increases in thickness. In air at a pressure of .078 millim. this molecular distarbance extends for at least 8 millims. from the surface of the disk, forming an oblate spheroid around it.
b. The diameter of this dark space varies with the exhaustion ; with the kind of gas in which it is produced ; with the temperature of the negative pole; and, in a slight degree, with the intensity of the spark. For equal degrees of exhaustion it is greatest in hydrogen and least in carbonic acid, as compared with air.
C. The shape and size of this dark space do not vary with the distance separating the poles; nor, only very slightly, with alteration of battery power, or with intensity of spark. When the power is great the brilliancy of the unoccupied parts of the tube overpowers the dark space, rendering it difficult of observation; but, on careful scrutiny, it may still be seen unchanged in size, nor does it alter even when, with a very faint spark, it is scarcely visible. On still further reduction of the power it fades entirely away, but without change of form.
The author describes numerous experiments, devised to ascertain if this visible layer of molecular disturbance is identical with the invisible layer of molecular pressure or stress, the investigation of which has occupied him for some years.
The Electrical Radiometer. One of these experiments is as follows :-An ordinary radiometer is made, with aluminium disks for vanes, each disk coated with a film of mica. The fly is supported by a hard steel cup instead of a glass cup, and the needle point on which it works is connected by means of a wire with a platinum terminal sealed into the glass. At the top of the radiometer bulb a second terminal is sealed in. The radiometer can therefore be connected with an induction coil, the movable fly being made the negative pole.
Passing over the phenomena observed at low exhaustions, the author finds that, when connected with the coil, a halo of a velvety violet light forms on the metallic side of the vanes, the mica side remaining dark throughout these experiments. As the pressure diminishes, a dark space is seen to separate the violet halo from the metal. At a pressure of half a millim. this dark space extends to the glass, and positive rotation commences.
On continuing the exhaustion, the dark space further widens out and appears to flatten itself against the glass, and the rotation becomes very rapid.
When aluminium cups are used for the vanes instead of disks backed with mica, similar appearances are seen. The velvety violet halo forms over each side of the cup. On increasing the exhaustion the dark space widens out, retaining almost exactly the shape of
The bright margin of the dark space becomes concentrated at the concave side of the cap to a luminous focus, and widens ont at the convex side. On further exhaustion, the dark space on the convex side touches the glass, when positive rotation commences, becoming very rapid as the dark space further increases in size, and ultimately flattening against the glass.
Convergence of Molecular Rays to a Focus. The subject next investigated is the convergence of the lines of force to a focus, as observed with the aluminium cup. As this could not be accomplished during rapid rotation, an instrument was made, having the cup-shaped negative pole fixed, instead of movable. On exhaustion, the convergence of the lines of force to a focus at the concave side was well observed. When the dark space is very much larger than the cup, it forms an irregular ellipsoid drawn in towards the focal point. Inside the luminous boundary a focus of dark violet light can be seen converging, and, as the rays diverge on the other side of the focus, spreading beyond the margin of the dark space; the whole appearance being strikingly similar to the rays of the sun reflected from a concave mirror through a foggy atmosphere.
Green Phosphorescent Light of Molecular Impact. At very high exhaustions the dark space becomes so large that it fills the tube. Careful scrutiny still shows the presence of the dark violet focus; and the part of the glass on which fall the rays diverging from this focus shows a sharply-defined spot of greenish-yellow light. On still further exhaustion, and especially if the cup is made positive, the bulb becomes beautifully illuminated with greenish-yellow phosphorescent light.
This greenish-yellow phosphorescence, characteristic of high exhaustions, is frequently spoken of in the paper. It must be remembered, however, that the particular colour is due to the special kind of soft German glass used. Other kinds of glass phosphoresce in a different colour. The phosphorescence takes place only under the influence of the rays from the negative pole. At an exhaustion of 4 M*, no light other than this is seen in the apparatus. At :9 M the phosphorescence is about at its maximum. When the exhaustion reaches 15 M the spark has a difficulty in passing, and the green light appears occasionally in flashes only. At :06 M the vacuum is almost non-conductive, and a spark can be forced through only by increasing the intensity of the coil, and well insnlating the tube and wires leading to it. Beyond that exhaustion nothing has been observed.
Focus of Molecular Energy. In an apparatus specially constructed for observing the position of the focus, the author found that the focal point of the green phosphorescent light was at the centre of curvature, showing that the molecules by which it is produced are projected in a direction normal to the surface of the pole. Before reaching the best exhaustion for the green light, another focus of blue-violet light is observed ; this varies in position, getting further from the pole as the exhaustion increases. In the apparatus described, at an exhaustion of 19:3 M, these two foci are seen simultaneously, the green being at the centre of curvature, while the blue focus is at nearly twice the distance.
Nature of the Green Phosphorescent Light. The author adduces the following characteristics of the green phosphorescent light, as distinguishing it from the ordinary light observed in vacuum-tubes at lower exhaustions :
a. The green focus cannot be seen in the space of the tube, but where the projected beam strikes the glass only.
b. The position of the positive pole in the tube makes scarcely any difference to the direction and intensity of the lines of force which produce the green light. The positive pole may be placed in the tube either at the extremity opposite the negative pole, or below it, or by its side.
c. The spectrum of the green light is a continuous one, most of the red and the higher blue rays being absent; while the spectrum of the light observed in the tube at lower exhaustions is characteristic of the
* M signifies the millionth of an atmosphere.