536 



NA TORE 



{Oct. 7, 1880 



does not vary \vilh the length of the electrodes. The 

 further removed the glass walls are from the two elec- 

 trodes the greater is the width of the surfaces. All these 

 and other properties follow at once if we consider that 

 the luminosity is produced by the intersection of the rays 

 proceeding from the cathocles with the glass walls. If 

 M'e increase the thickness of one of the electrodes, the 

 size of the dark surface nearest to it is increased. We 

 now turn, to the experiments which have been made in 

 order to clear up the cause of the phenomena. By means 

 of very ingenious experiments Dr. Goldstein proves that 

 it is only light produced by the nearer electrode which is 

 seen within the boundary of the dark surface, for although 

 we have called them dark, they are only so by contrast, 

 and they show a faint phosphorescence. Dr. Goldstein 

 had, in a former paper, shown that when the cathode is 

 perfectly smooth, the phosphorescent light produced by 

 the glow shows inequalities. By twisting the aluminium 

 electrodes he could obtain a series of spiral curves in the 

 phosphorescent light more luminous than the rest. If 

 one of the two cathodes is twisted in such a way and 

 connected with the other, the spiral curves are interrupted 

 in the dai-k space which is removed from the twisted elec- 

 trode, but they are visible in the dark surface nearest to it. 



The dark surface cannot be considered as enlarged 

 shadows only of the electrodes, for their shape is different, 

 but they might as regards shape be considered as shadows 

 of the second and non-luminous layer of the negative 

 glow. This remark we believe to be of importance, but 

 Mr. Goldstein shows that they cannot really be such 

 shadows, for they appear e\'en w'hen by an approach of 

 the two electrodes the two non-luminous layers fiise into 

 one and so lose their individuality. 



The following experiment proves the repulsion. A 

 metallic diaphragm is introduced between the two 

 cathodes. A , small hole is made in the diaphragm 

 with its centre in a line joining the electrodes. Only 

 some of the rays proceeding from each cathode can now 

 reach the next, and consequently we observe only a small 

 phosphorescent speck at the opposite side of the glass 

 wall if one of the electro^los is insulated, but the dark 

 shadow of the nearest electrode is visible in this phos- 

 phorescent speck. If now the two cathodes are joined 

 the phosphorescent speck is seen to divide into two which 

 separate and clearly show that the rays producing the 

 phosphorescent light must have suffered a deflection as 

 soon as the two cathodes were joined. Further experi- 

 ments show that the dellection takes place at right angles 

 to the surface of the electrode, and that it takes place at 

 sensible distances from the repelling cathode, although it 

 rapidly decreases in strength. Near the edge of a 

 repelling cathode the repulsion does not take place in a 

 normal direction, and Dr. Goldstein draws again a 

 distinction between elements of a surface according as 

 they are removed or near an edge. We believe this 

 distinction to be unnecessary, and that all phenomena 

 are explained by the fact that all parts of the electrode 

 are repelling, and not only the elements nearest to the 

 deflected ray. . 



Some remarkable secondary phenomena take place in 

 a deflected system of rays. If, for instance, a system of 

 rays forming a cone of narrow aperture passes near a 

 second cathode, it is not only deflected but the aperture 

 of the cone is increased. The phenomena are such as 

 would be produced if a cathode not only repels the rays 

 but also induces a state in the particles forming the ray 

 such that they now repel each other. Also parts of the 

 same cathode repel rays proceeding from other parts, and 

 the repulsion increases the thicker the electrode. All 

 these facts are illustrated and proved by a series of well- 

 arranged experiments. Dr. Goldstein next examines the 

 influence of an anode, but we shall not follow him, as it is 

 found that the effect of an anode is exceedingly small, 

 and most likely always produced by secondary causes. 



The deflection is the same in all gases : air, hydrogen, 

 carbonic oxide, and magnesium vapour having been tried. 



The deflection is independent of the metal of which 

 the cathode is formed ; it is independent of the pressure. 

 It is also independent of the intensity of discharge when 

 the two electrodes are in metallic contact, so that the 

 current is equally divided between the two cathodes. 

 But remarkable changes take place if the current is not 

 so equally divided. This can be done by joining the 

 electrodes not metallically, but with a bad conductor, as 

 for instance a moist thread. It is then found that the 

 dark surface nearest the cathode through which the 

 smaller discharge passes is much reduced in size, while 

 the other dark surface is increased. It follows from 

 experiments such as this that the repulsion does depend 

 on the intensity of discharge, but that while a cathode 

 through which more electricity passes more strongly 

 repels, a ray which proceeds from such a cathode is less 

 strongly deflected. If therefore we have seen that the 

 dark surfaces do not vary in size, whatever the intensity 

 of discharge, if the two poles are connected with a piece 

 of metal ; this is due to the fact that each cathode repels 

 more strongly, but that the rays of the other electrode 

 (owing perhaps to the greater velocity of the molecules 

 proceeding from it) are less easily deflected, and that the 

 two effects counterbalance each other. Dr. Goldstein 

 considers, rightly no doubt, that the shadows seen when 

 one apparently insulated metallic body is introduced 

 between the cathode and the glass are due to a similar 

 repulsion, because we may consider that a small part of 

 the discharge always passes through such a body, the 

 glass into which the body is necessarily sealed not being 

 an absolute non-conductor. The shape of the shadow 

 confirms this supposition. 



Dr. Goldstein has also obtained "the repulsion from elec- 

 trodes consisting of glass and mica, so that the metallic 

 or non-metallic nature of the electrode does not influence 

 the phenomena. He has also proved that the source ot 

 electricity is immaterial, as might have been expected. 



Dr. Goldstein has also endeavoured to prove that 

 the deflecting power of a cathode does not act through 

 a solid screen, but he has chosen metallic screens for his 

 experiment. 



If the repulsion is of _^ the nature of electric repulsion 

 a metallic body might ^act as a screen, while a non- 

 metallic body would allow two bodies on opposite sides of 

 it to repel each other. As it is impossible to form any 

 idea on the cause of these phenomena unless we know 

 whether the deflecting power is cut oft" by any solid body, 

 it is much to be wished that Dr. Goldstein will repeat his 

 experiments with non-metallic screens. 



In the last part of his book Dr. Goldstein discusses 

 various theories which might be proposed and have been 

 proposed for the explanation of the phenomena taking 

 place in the neighbourhood of the negative electrode. The 

 result is that none of them are satisfactory. While this 

 no doubt is true. Dr. Goldstein is too severe, we believe, 

 in his criticisms of some of the suggestions which have 

 been made, and which may, in our opinion, after all con- 

 tain the germ of the true explanation, though in their 

 present shape they may not be quite satisfactory. Some 

 of the facts which to Dr. Goldstein are sufficient to reject 

 a theory may, we believe, be explained without putting 

 too great a strain on our present ideas, and sometimes we 

 believe Dr. Goldstein to be in error, as when, for instance, 

 he says that a body must necessarily move in a line of 

 force. It would at least be a sad look-out for our earth if 

 this was true, and Dr. Goldstein would in that case have 

 occasion to study before long the electric phenomena on 

 the surface of the sun. We will hope, for the sake 01 

 science, that both Dr. Goldstein and his molecules do not 

 always move in lines of force, and that he will often 

 favour us with such interesting and valuable contributions 

 as the one before us. ARTHUR SCHUSTER 



