THE INTELLECTUAL GESERVER. MARCH, 1-66. STRATIFIED DISCHARGES IN VACK PA MR. CASSIOT'S FN, ERIMENTS. (With a Coloured Plate) Top ok relectricians were familiar wit: •* J3 with galvanic electricity a high d gree which, wida w years spee yang Laderies containing an P., 1.. The intruction of coil ranca 2.4% na leerrnts of at intensity to be obtained by the use of oni » two gaices; and when these machines wro prfected by kori, very powerful effects were readily produced. The mople of a coil machine is that of accumula ng the e Pets 3 erie- of inductions, An internisting curi ut galvanic cloeity is passed threng a thick cope wire wound round haale of aron wires, which in rapid alternations become Cease to be powerfully retie. Oor this primary great len, h of tuin were, carred by irsumtiog is staged in else fiting cols one over dig othe,, in mist. thents three or four mes of th a wino ar fan this way. In the centre of the hick ori; - 1 of soft iron becomes a wet the more cat དྷ་མཚོན་མཐོན(I by a corrent. When thakes place mer of soft it on, so led flat as soch rond is rupted The feet of r intheyas of soft iron in the centre of 2, ie, and the tile bammer, conson gatongs through the elasticity of its langka The enment is then renewed, to be bag' At ex ch renewal. fresh current, prodde wen apto the thia egi, ea the gr gracz the force of th vel etrie as TA m them. A.-NO. TI, THE INTELLECTUAL OBSERVER. MARCH, 1866. STRATIFIED DISCHARGES IN VACUUM TUBES. MR. GASSIOT'S EXPERIMENTS. (With a Coloured Plate.) THE older electricians were familiar with the beautiful auroral effects obtained by transmitting frictional electricity through glass vessels partially exhausted of air. To obtain analogous effects with galvanic electricity a high degree of tension is required, which, until a few years since, could only be obtained by employing batteries containing an immense number of insulated cells. The introduction of coil machines enabled currents of great intensity to be obtained by the use of one or two galvanic cells; and when these machines were perfected by Ruhmkorff, very powerful effects were readily produced. The principle of a coil machine is that of accumulating the effects of a series of inductions. An intermitting current of galvanic electricity is passed through a thick copper wire wound round a bundle of iron wires, which in rapid alternations become and cease to be powerfully magnetic. Over this primary coil a great length of thin wire, covered by insulating materials, is arranged in close-fitting coils one over the other. In large instruments three or four miles of thin wire are disposed of in this way. In the centre of the thick primary coil the mass of soft iron becomes a magnet the moment the wire, is traversed by a current. When this takes place it attracts a little hammer of soft iron, so placed that as soon as it moved the current is interrupted. The effect of this interruption is that the mass of soft iron in the centre of the coil ceases to be magnetic, and the little hammer, ceasing to be attracted, returns, through the elasticity of its handle, to its former place. The current is then renewed, to be broken and renewed in very rapid alternations. At each renewal of the current through the primary coil, a fresh current, produced by induction, is thrown into the thin coils, and the greater the number of these coils, the greater the force of the electric discharge to be obtained from them. VOL. IX.-NO. II. G The vacuum tubes, or vessels through which these discharges are passed, in order to obtain certain remarkable luminous effects, are of various shapes; in some cases the air in them is exhausted by making them form a part of a Torricellian vacuum, and then minute quantities of any gas required are introduced. In other cases such tubes are filled with carbonic acid gas, part of which is removed by means of an airpump, and nearly all the remainder absorbed by caustic potash. The atmospheric pressure inside one of Geissler's vacuum tubes is said not to exceed half a millimetre,* and is often much less. The general character of the discharge of a powerful induction coil through one of the vacuum tubes just described, is an alternation of luminous and dark bands, accompanied by a quivering motion. When the discharge takes place through a tube containing an infinitesimal quantity of atmospheric air, the light of the positive pole is fiery red, that of the negative pole, violet. A hydrogen vacuum tube, in which bulbs alternate with capillary tubes, shows white light in the former, and red in the latter, dark bands alternating with light ones. Carbonic acid tubes give a greyish light, and nitrogen orange red. The dark bands or striæ vary in shape according to the nature of the so-called vacuum.† Nothing can exceed the beauty of this class of experiment, and it is frequently heightened by the employment of tubes made of glass tinged with uranium, which becomes phosphorescent under the influence of the electric light. In one of the pieces of apparatus devised by Mr. Gassiot a stream of coloured fire falls into a series of different-coloured cups, while in another, a vacuum, tube is made to revolve, producing a wheel of splendid fire. We are glad to observe that several opticians have recently produced coil machines and vacuum tubes on a small scale at a moderate price, so that this interesting branch of study has a chance of becoming popular, and those who cannot witness the magnificent exhibitions so often made at London soirées may be able to obtain at pleasure similar effects in their own homes. Mr. Gassiot, to whom this and other branches of electrical science are under deep obligations, possesses a magnificent collection of vacuum tubes, amounting to more than four hundred, arranged in a convenient laboratory duly labelled, and their peculiarities registered in what we may designate an electrical ledger. Having tried innumerable experiments with the aid of Ruhmkorff's coils, Mr. Gassiot determined on the * 760 millimetres correspond with 29,922 English inches of mercurial pressure. † A real vacuum would not transmit the current at all. construction of the most powerful constant battery yet made. For this purpose he caused four thousand cells containing carbon and amalgamated zinc elements, to be arranged on a series of trays, extending in his laboratory from the ceiling to the ground. These cells are excited by a solution of sulphate of mercury. Under the influence of the electric current, this solution is decomposed, the sulphuric acid attacking the zinc, forms a sulphate which remains in solution, and the mercury which is liberated gives the zinc a fresh coating of amalgam, and keeps down local action. The frames holding this magnificent apparatus are arranged at certain intervals, insulated wires are attached, and the number of cells set in motion by making connections at any point is made known by appropriate labels. Before the currents from this battery reach the tubes, they pass through an apparatus by which they can be exposed to definite and measured quantities of resistance, in the shape of spaces of air and spaces of water. We have prefaced a description of the remarkable experiments which the coloured plate prefixed to this article illustrates, and which is copied from a drawing kindly lent by Mr. Gassiot, by the preceding elementary remarks, because we believe that many persons not previously acquainted with this branch of investigation will take great interest in it, if assisted by the preliminary information thus afforded. Amongst the large collection of vacuum tubes in Mr. Gassiot's collection, one made by Geissler yielded anomalous and most remarkable results. These, which were described by Mr. Gassiot to the British Association form the subject of our plate. When a discharge of from 1200 to 4000 cells of the constant battery is passed through this tube, after suffering a varying amount of resistance through the interposition of a column of water of different lengths, a series of striking effects are obtained. The resisting water column is contained in a glass tube half an inch in diameter and three feet long. At one end of this tube a wire is introduced, connected with one pole of the battery, and at the other end is a second wire, connected with the vacuum tube. When the discharge has to traverse the whole column of water before reaching the vacuum tube, a luminous appearance fills the latter without exhibiting any appearance of stratification. By depressing one wire in the water column, and thus reducing the resistance by shortening its acting length, small crescentshaped discs of light are produced in quick succession, beginning at the positive pole, and alternating with dark bands. They speedily fill the whole length of the vacuum tube. A further depression of the conducting wire in |