238 



NA TURE 



[July 8, 1897 



and with a little more power doubles it, causing a distinct dark 

 •line down its middle. The same effect occurs with lithium and 

 thallium lines. 



At higher temperature, and with the flame partially behind 

 the field, when each sodium line appears as a broad hazy-edged 

 double, magnetisation greatly widens the doubling, pushing 

 asunder the bright components very markedly ; stronger magnet- 

 isation reverses the middle of the widened dark band, giving a 

 triple appearance ; stronger magnetisation still reverses the 

 middle once more, giving a quadruple appearance to the line. 

 In every case a nicol, suitably placed, cuts off all the magnetic 

 effect and restores the original appearance of the line. 



The same thing is seen when salts of lithium or of thallium 

 are introduced into the flame ; and the components of the 

 doubled red lines are more widely separated than the com- 

 ponents of the doubled green lines, the effect being proportional 

 to wave-length. The most interesting line to try was the red 

 cadmium line, since this has been proved to be of specially 

 simple constitution by Michelson. We have recently been able 

 to get the cadmium spectrum well developed by means of a sort 

 of spark arc between the magnet poles, maintained by an in- 

 duction coil excited by an alternating machine, and we find 

 that the magnetic doubling of the chief lines occurs in precisely 

 the same way with the spark spectrum as with the flame spec- 

 trum, and that the red cadmium line behaves in the same way 

 as the others. The magnetic effect is better seen from a direc- 

 tion perpendicular to the line of force when a nicol is interposed 

 in the path of the light, but rotation of the nicol, through 90°, 

 cuts it entirely off, accurately so where a small spark is the 

 source of light. 



June 17. — " Kathode Rays and some Analogous Rays." 

 By Silvanus P. Thompson, F.R.S. 



(i) The size of the kathodic shadow of an object depends 

 upon its own electric state, as already found by Crookes {Phil. 

 Trans., 1879, P^^t ii, p. 648). If it is negatively electrified the 

 shadow expands. If it is positively electrified the shadow con- 

 tracts. The position, as well as the size of a kathodic shadow, 

 may be affected electrostatically ; the rays which cast the 

 shadow being repelled from a neighbouring body if the latter is 

 negatively electrified. In some cases the contraction of the 

 shadow of a narrow object that is made positively electrical 

 (anodic) may go so far that the luminous margins approach and 

 even overlap, giving the appearance of a bright or negative 

 shadow in place of a dark one. The enlargement of a shadow 

 when the object is made kathodic, and the diminution of the 

 shadow when the object is made anodic, both depend upon the 

 degree of exhaustion of the tube ; and both are augmented up 

 to a certain point by raising the degree of exhaustion. The 

 enlargement when the object is made kathodic vastly surpasses 

 the diminution when the object is made anodic. Kathode rays 

 are capable of being deflected electrostatically ; being apparently 

 strongly repelled from a neighbouring kathodic surface, and less 

 strongly attracted towards a neighbouring anode. Two kathode 

 beams from two small disc kathodes can cross through or 

 penetrate one another without interfering with another. 



(2) Objects protected by a non-conducting layer of glass do 

 not at moderately low exhaustions, when jmade kathodic, repel 

 or deflect kathode rays, and their shadow does not enlarge. But 

 at a certain minimum exhaustion they suddenly exert an electro- 

 static deflection. Naked ob'ects made kathodic deflect the 

 kathode rays at all exhaustions. 



(3) Kathode rays cannot be concentrated by reflection either 

 from a non-conducting or a conducting surface, nor by passage 

 through a metal tube which is itself negatively electrified. 



(4) When kathode rays strike upon an internal metal target 

 or anti-kathode there are emitted from the latter (both at 

 exhaustions lower than suffice to produce Rontgen rays, and at 

 exhaustions at which those rays are also produced) some internal 

 rays resembling ordinary kathode rays in the following 

 respects : — They produce a similar luminescence of the glass ; 

 they cast shadows of objects ; they are susceptible of deflection 

 both magnetically and electrostatically. But they produce no 

 Rontgen rays where they fall upon the glass surface. They do 

 not follow either the law of specular reflection, nor that of 

 diffuse reflection, but are emitted from the anti-kathode surface 

 apparently according to a similarly anomalous distribution to 

 Rontgen rays, i.e. with nearly equal intensity, at all angles up 

 to 90° with the normal. It is proposed to call these rays/ara- 

 kathodic rays in contradistinction to the ordinary or ortho-kathodic 

 rays. From the similarity of their distribution with that of the 



NO. 1445, VOL. 56] 



Rontgen rays it is inferred that the physical processes concerned 

 in their production are identical. These para-kathodic rays are 

 emitted from the anti-kathode both when the latter is made an 

 anode, and when it is neutral or even made kathodic. P'rom 

 an anti-kathode there may proceed at one and the same time, 

 and in one and the san)e direction para-kathodic rays and 

 Rontgen rays, which, meeting an interposed object, may cast 

 simultaneously two shadows — a para-kathodic shadow on the 

 glass, and a Rontgen shadow on an external screen of barium 

 platinocyanide. The former shadow can be deflected by a 

 magnet, the latter cannot. The former shadow expands if the 

 object is made kathodic ; the latter does not. 



(5) If thin metal screens are used to sift the kathode rays the 

 luminescent phenomena change. The rays of least penetrating 

 power appear to be most susceptible to magnetic and electro- 

 static forces. The various constituents of a heterogeneous kathode 

 beam are emitted in various proportions at different degrees of 

 exhaustion. In the kathode rays emitted at higher degrees of 

 exhaustion there is a greater proportion of the less-deflectable 

 rays. The least-deflectable rays are those which most readily 

 penetrate through a perforated screen when that screen is itselt 

 negatively electrified. 



When ordinary kathode rays fall upon a perforated screen 

 which is itself made kathodic, or are attempted to be passed 

 through a negatively electrified tube, there emerge beyond the 

 screen or tube some rays, here termed dia-kalhodic rays, which 

 differ from the ortho-kathodic, and also from the para-kathodic 

 rays. These dia- kathodic rays are not themselves directly 

 deflected by a magnet. They show themselves as a pale blue 

 cone or streak. Where they fall on the glass they do not excite 

 the ordinary fluorescence of the glass. The dia-kathodic rays 

 excite, however, a different or second kind of fluorescence ; the 

 tint in the case of soda-glass being a dark orange. Intervening 

 objects in the beam or cone of dia-kathodic rays cast shadows. 

 The orange fluorescence evoked on soda-glass by the dia- 

 kathodic rays shows in the spectroscope the D lines of sodium 

 only. The shadows cast by dia-kathodic rays are not deflected 

 by the magnet, nor do they change their size when the object is 

 electrified. 



" Fifth Report to the Royal Society Water Research 

 Committee." By H. Marshall Ward, F.R.S., Professor of 

 Botany in the University of Cambridge. Presented to the 

 President and Council, December 10, 1896. 



The following conclusions show the principal points resulting 

 from three years' study of the Bacterial Flora of the Thames : — 



( 1 ) Very many forms occur in the Thames, some of which are 

 pathogenic under certain conditions. 



(2) The " species " of the descriptive hand-books — principally 

 medical — are frequently not species at all, in the botanical sense, 

 but varieties, or growth-forms, the distinctive characters of 

 which are not constant. These so-called species need revision 

 and grouping around types, which may turn out to be the true 

 species. 



(3) The characters derived from the behaviour of colonies are 

 not sufficient for the determination of species, and how far they 

 may be employed in conjunction with other characters will only 

 be elucidated by advances in our knowledge of the way the 

 colonies are built up by the growing bacteria on the given 

 media. 



(4) The effects of definite changes in the environment on the 

 media are of great importance, but have hardly been noticed as 

 yet. Plate-colonies on gelatine, for instance, develop quite 

 differently, according to the condition of the gelatine ; so that a 

 feeble and slow-growing bacterium produces colonies quite unlike 

 those developed by the same species when vigorous and quickly 

 growing, not only owing to its peculiarities of growth as a feeble 

 form, but also because the gelatine has altered during the inter- 

 vening period. 



(5) The effect of changes of the environment on the growing 

 organism itself is recognised as important. 



(6) With especial reference to the Thames bacteria, the past 

 history of the organism isolated from the river implies causes o. 

 variation. The river water is a poor nutritive medium, and the 

 organism is exposed to great changes of temperature, light, 

 movement, &c. , during its sojourn therein. Consequently the 

 time it has been in the river affects the behaviour of the 

 organism when isolated, just as we know that a bacterium is 

 affected by the previous conditions of its culture in other media. 

 Hence two colonies on a plate may look very different, and yet 

 belong to the same species, one being developed from a cell 



