158 



NATURE 



\yune2A,, 1875 



the other. And further, that any disturbance affecting the 

 column of striaa due to one current affects similarly, with refer- 

 ence to absolute space, that due to the •ther, so that the double 

 column moves, if at all, as a solid or elastic mass. And this 

 fact is the more remarkable if we consider, as is easily observed 

 in a revolving mirror, that these currents are alternate, not only 

 in direction, but also in time, and that no one of them is pro- 

 duced until after the complete extinction of its predecessor. 

 And it is also worthy of note that this association of striae is not 

 destroyed, even when the two currents are separated more 

 or less towards opposite sides of the tube by the presence of a 

 magnetic pole. There seems, however, to be a tendency in that 

 case lor the stria: of one current to advance upon the positions 

 occupied by those of the reverse current, giving the whole 

 column a twisted appearance. But as there is no trace, so far as 

 the author's observations go, of this association of alternate dis- 

 charges when produced by the ordinary break, we seem led to 

 the conclusion that a stratified discharge, on ceasing, leaves the 

 gas so distributed as to favour, during a very short interval of 

 time, a similar stratification on the occurrence of another dis- 

 charge, whether in the same or in the opposite direction. An 

 explanation of the fact that the stride of alternate discharges 

 occupy alternate and not similar positions is not obvious, and 

 probably demands a better knowledge of the nature of the striae 

 than we possess at present. 



The column of striae, which usually occupy a large part of the 

 tube from the positive towards the negative terminal, have 

 hitherto been described as stationary, except as disturbed by 

 irregularities of the break. The column is, however, frequently 

 susceptible of a general motion, or "flow," either from or 

 towards the positive pole, say a forward or backward flow. A 

 similar phenomenon was observed by Mr. Gassiot in some tubes 

 with his large battery, but the author is not acquainted with the 

 exact circumstances under which it was produced. This flow 

 may be controlled, both in velocity and in direction, by resist- 

 ance introduced into the circuit, or by placing the tube in a mag- 

 netic field. The resistance may be introduced in either the 

 primary or the secondary circuit. For the former arrangement 

 the author successfully employed a set ot resistance-coils, sup- 

 plemented by a rheostat. For the secondary current, as well as 

 for the Holtz machine, he has used an instrument devised 

 and constructed by his assistant, Mr. P. Ward, to whose intelli- 

 gence and skill he is much indebted throughout this investiga- 

 tion, intended for fine adjustment. Wherever the resistance be 

 introduced the following law appears to be established by a 

 great number and variety of experiments, viz., that, the striae 

 being previously stationary, an increase of resistance produces 

 a forward flow, a decrease of resistance a backward flow. The 

 author has generally found that a variation of 3 or 4 ohms, 

 or, under favourable conditions, of i or 2 ohms, is suffi- 

 cient to produce this effect. But as an alteration in the 

 current not only affects the discharge directly, but also reacts 

 upon the break, the effect is liable to be masked by these indirect 

 causes. The latter, so far as they are dependent upon a sudden 

 alteration of the resistance, may be diminished by the use of the 

 rheostat ; but when the striae are suiBciently sensitive to admit 

 the use of this delicate adjustment, some precautions are neces- 

 sary to ensure perfect uniformity of current, so as to avoid dis- 

 turbances due to uneven contact in the rheostat itself. 



When the striae are flowing they preserve their mutual dis- 

 tances, and do not undergo increase or decrease in their numbers. 

 Usually one or two remain permanently attached to the positive 

 electrode ; and as the moving column advances or recedes, the 

 foremost stria diminishes in brilliancy until, after travelling over 

 a distance less than the intervals between the two striae, it is lost 

 in darkness. The reverse takes place at the rear of the column. 

 As the last stria leaves its position, a new one, at first faint and 

 shadowy, makes its appearance behind, at a distance equal to 

 the common interval of all the others. This new one increases 

 in brilliancy until, when it has reached the position originally 

 occupied by the last stria, when the column was at rest, it 

 becomes as bright as the others. The flow may vary very much 

 in velocity ; it may be so slow that the appearances and disap- 

 pearances of the terminal striae may be watched in all their 

 phases, or it may be so rapid that the separate strias are no 

 longer distinguishable, and the tube appears as if illuminated 

 with a continuous discharge. In most cases the true character 

 - of the discharge, and the direction of the flow, may be readily 

 distinguished by the aid of a revolving mirror. In some tubes, 

 especially in those whose length is great compared with their 



diameter, the whole column does not present the same phase of 

 flow ; one portion may be at rest while another is flowing, or 

 even two conterminous portions may flow in opposite directions. 

 This is seen also in very wide tubes, in which the striae appear 

 generally more mobile than in narrow ones. But in all cases 

 these nodes or junctian-points of the flow retain their positions 

 under similar conditions of pressure and current ; and it therefore 

 seems that, under similar conditions, the column in a given tube 

 always breaks up into similar flow-segments. 



These nodes will often disappear under the action of a mag- 

 netic pole. Thus, if the first segment, measured from the positive 

 terminal, be stationary and the second be flowing backwards 

 {i.e. from - to -(- ), a magnetic pole of suitable strength, placed at 

 the distant end of the latter, will stop its flow, and the whole 

 column will become stationary throughout. An increase in the 

 strength of the magnet, or a nearer approach of it to the tube, 

 will produce a general forward flow of the column. 



The phenomena of the flow, as well as others of not less inte- 

 rest, are capable of being produced with the Holtz machine. It 

 is well known that stratified discharges, similar to those produced 

 by an induction-coil working with an ordinary break, may be 

 produced by such a machine, provided that it be furnished with 

 the usual Leyden jars, and a high resistance (usually a piece o. 

 wetted string) be interposed in the circuit. The absence of 

 either of these conditions was supposed to destroy the striae and 

 to render the discharge continuous. Experiments which the 

 author has recently made, but do not describe on the present 

 occasion, tend in part, but only in part, to confirm this view. 

 They show that for the production of stria both quantity and 

 resistance are necessary, that the discharge must occupy a certain 

 short, perhaps, but finite time, or, as it may also be expressed, 

 that a continuous current is an essential element. 



Now, seeing that every tube must offer some resistance, and 

 also that by adjusting the height of the vertical condensors of 

 the machine (or length of air-spark interposed in the circuit) we 

 had the means of altering the quantity in the discharge, it 

 seemed worth while to try whether, by a suitable adjustment of 

 the parts, phenomena similar to those brought out by the coil 

 and high break might not be produced by the machine. And 

 this proved to be very easy of attainment in tubes which had 

 been successfully used by the coil ; and not only so, but the 

 character of the flow therein shown confirmed in a very striking 

 and simple manner the effects of resistance described above. 



The connections being made in the usual way, and no air- 

 spark being admited into the circuit, a vacuum-tube of carbonic 

 oxide, about 60 centims. in length and 4-5 centims. in outside 

 diameter, gave, when the plates of the machine revolved at about 

 six times per second, a rather confused discharge. As the speed 

 was increased a rapid forward flow of the stria was readily dis- 

 cerned ; and on a still further increase to about ten revolutions 

 per second, the flow, first in one part and then throughout nearly 

 the whole length of the tube, slackened its pace and stopped, 

 and ultimately reversed its motion. An increase of speed is 

 equivalent to an overcoming or a diminution of resistance in the 

 circuit, a diminution of speed to an augmentation of resistance. 

 Hence the phenomena of flow produced by the machine agree 

 with those produced by the coil. 



The author concludes by referring to the effects obtained with 

 sulphurous acid and other tubes, and by describing the resist- 

 ance-coil used for the secondary current. 



Chemical Society, June 17. — Prof. Abel, F.R.S., in the 

 chair. —Notes on the chemistry of tartaric and citric acid, by Mr. 

 R. Warrington, gives many important particulars connected with 

 the manufacture of these acids : and also detailed accounts of 

 the methods of analysis — many of them novels of the various raw 

 materials from which they are made. — After this the Secretary 

 read a communication on the action of nitric acid on copper, 

 mercury, &c. , especially in the presence of metallic nitrates, by 

 Mr. J. J. Ackworth. — Dr. Gladstone then gave a short account 

 of the decomposition of water by the joint action of aluminium 

 and aluminium iodide, bromide, and chloride, including instances 

 of reverse action, by himself and Mr. Tribe. — The other papers 

 were on nitrosyl-bromide and on sulphuro-bromide, by Mr. 

 M. M. P. Muir. — On achrematite, a new molybdo-arseniate of 

 lead from Mexico ; and on certain new reactions of tungsten, 

 both by Prof. J. W. Mallet ; and on the action of chlorine on 

 acetamide, by Dr. Prevost. 



Geological Society, June 9.— John Evans, V.P.R.S., pre- 

 sident, in the chair. — The following communications were read : 



