May 8, 1879] 



NATURE 



47 



versed, the orange line well reversed, and the green, though with 

 difficulty, distinctly reversed ; the violet line, much expanded, 

 showed no rever-al. The authors conclude that the green line 

 really belongs to lithium, and not to cfesium, since the blue lines 

 of the latter metal, so easily reversed, never appeared. 



In the care of rubidium, the more refmngible of the red lines 

 was seen as a black line on a continuous background, but this 

 background of light did not extend so low as to allow the reversal 

 of the extreme ray of rubidium to be obferved. 



With metallic indium the two characteristic lines were seen 

 strongly rever^ed, but r.o other ; metallic gallium also gave its 

 two characteristic lines reversed, the more refrangible being the 

 less strongly so. 



Aluminium gave no reversal of any of its lines, except the 

 two between the Fraunhofer lines H. It was noticed that the 

 addition of aluminium to either copper or silver in the lime tubes 

 caused the copper or silver lines, previously predominant, to 

 fade, while the calcium lines came out instead with marked 

 brilliance. 



Reviewing the series of reversals which they have observed, 

 the authors remark that in many cases the least refrangible of 

 two lines near together is the most easily reversed, as has been 

 previously remarked by Cornu. Thus, in the case of barium 

 (though there is no very distinct grouping of the lines of that 

 metal), taking the rays in order, the line wave-length 5S35 

 is readily reversed, while that with wavelength 5518 is less 

 easily reversed ; the line wave length 4933 is comparatively 

 easily reversed, whereas that with wave-Ieng'h 4899 has not 

 been reversed. On the other hand, the line wave-length 4553 

 has been reversed, but not the line wave-length 4524. In 

 the case of strontium, the lines wavelength 4831 and 4812 have 

 been reversed, V;Ut not the line wave- length 4784, and the two 

 lines wavelength 4741 and 4721 remain both unreversed. In 

 the group of five lines of calcium, wave-length 4318 to 4282, it 

 is only the middle line wave-length 4302 which has been re- 

 versed. Of the potassium groups of lines wave-length 5829 and 

 581 1, 5802, 5782, the line wave-length 581 1 has not been re- 

 versed, and of the others the line wave-length 5802 is the first 

 to appear reversed. It is worthy of remark that the first of 

 these lines is faint and the last is the brijihtest of the group. 

 The group wave-length 5353, 5338, 5322 have been all reversed, 

 but the last of the three (5322) was the most difficult to reverse : 

 it is also the feeblest of the group. In the more refrangible 

 group, wave-length 5112, 5092, 5078, the least refrangible is 

 the only one reversed. 



Making a general summary of their results respecting the 

 alkaline earth metals, potassium and sodium, and having regard 

 only to the most characteristic rays, which for barium they 

 reckon as 21 in number, for strontium 34, for calcium 37, for 

 potassium 31, and for sodium 12, the reversals in their experi- 

 ments number respectively 6, 10, II, 13, and 4. That is in the 

 case of the alkaline earth metals about one-third, and these 

 chiefly in the more refrangible third of the visible spectrum ; 

 the number of characteristic rays remaining unreversed in the 

 more refrangible part of the spectrum being respectively 2, 

 5, and 4. In the case of potassium they reversed two in the 

 upper third, all the rest in the least refrangible third. These 

 experiments relate to mixtures of salts of these metals combined 

 with the action of reducing agents. 



In a table the authors show the relation between their obser- 

 Tations on reversals and Young's on the chromospheric lines. 



The authors point out that in Young's catalogue the green 

 coronal line (wavelength 5316) is almost as frequently present in 

 the chromosphere as the lines numbered I and 82, and D3 which he 

 suggested might belong to one substance, and they think that the 

 four lines may all belong to the same substance ; and they call 

 attention to certain analogies in the ratios of the wavelengths of 



■se four lines to those of the lines of hydrogen, lithium, and 



gnesium. 



April 24. — " On the Nature of the Fur on the Tongue," by 

 Henry Trentham Butlin, F.R.C.S. 



Tongue-fur consists chiefly of (i) Debris of food and bubbles 

 of mucus and saliva. (2) Epithelium. (3) Masses which appear 

 at first to consist of granular matter, but which are the gloea of 

 certain forms of schistomycetes. 1 hat the last-named of these 

 three is the essential constituent is proved by the fact that the 

 quantitity of the gloea corresponds roughly with the quantity of 

 I fur present, and that its position upon the tongue corresponds 

 i exactly with that of the fur, both covering the tops of the filiform 

 papilla;, but not usually lying between them. 



In order to ascertain the true nature of the gloea, and to ob- 

 tain it in a purer form, it was cultivated upon a warm stao-e. 

 Several fungi were discovered, but only two of these were present 

 in every instance. Micrococcus and Bacillus subtilis; and, as the 

 glcca produced artificially was similar to that existing naturally 

 in the tongue-fur, it is believed that fur is composed essentially 

 of these two fungi. Micrococcus developed freely and abundantly, 

 forming large masses of yellow or brownish-yellow colour. Ba- 

 cillus did not develop, but existed in greater or less abundance 

 in all the cases examined. Its development was probably pre- 

 vented by the presence of other developing organisms, from 

 which it was found impossible to separate it. It appeared to be 

 identical with the Leptothrix buccalis of Robin. Although it did 

 not develop under artificial conditions, it is probable that deve- 

 lopment takes place freely upon the surface of the tongue. Its 

 habitual occurrence there, and the presence of spore-bearing 

 filaments favour this view. 



Besides these fungi there were present, more or less constantly. 

 Bacterium termo, Sarcina ventriculi, Spirochceta plicatilis, and a 

 larger form of Spirillum (or rather Vibrio). Sarcina ventriculi 

 was frequently present, and generally developed quickly, forming 

 large masses of a yellow or yellowish-brown colour. Spirocha:ta 

 plicatilis occurred only in two or three of the sjiecimens 

 examined. Bacterium termo existed in some of the furs, and 

 twice developed with such rapidity that the whole of the fluid 

 was crowded with these organisms. 



The slime between and around the teeth was found to consist 

 of the same fungi as the tongue-fur, but the rods of Bacillus 

 were longer, probably owing to the disturbing causes being 

 fewer. 



Physical Society, April 26. — Prof. W. G. Adams in the 

 chair. — Mr. C. V. Boys gave an account of some experiments 

 made by Dr. Guthrie and himself on the subject of Arago's 

 rotation. The experiments were begun with a view to determine 

 if the drag on a copper disk when a magnet is made to revolve 

 beneath it, or on the magnet if the disk is made to revolve 

 above it, could be made use of for determining the velocity of 

 running machinery. They made the magnet revolve, and ob- 

 tained the angle of deflection of a disk suspended by a torsion 

 thread (the hair-spring of a watch). They found, as Snow, 

 Harris, and others found before, that other things being equal, 

 the drag is directly proportional to the speed, so that it the 

 torsion of the thread could be relied on, and the strength of the 

 magnet did not change, a perfect velocimeter could be con- 

 structed. They consider that this method is better than observ- 

 ing the deflection of a magnet over a revolving disk, ?s in this 

 case they are limited to less than a right angle, and changes 

 in the absolute magnetism of the earth would affect the 

 results. They also determined the effect of change of dis- 

 tance, thickness, diameter, and na'ure of the disk, &c., their 

 re ults agreeing with those of former experiments. They 

 observed that the effect of concentric circular cuts w as far greater 

 than that of even many radial cuts, and that w hen radial sectors 

 were entirely separated from each other, the effect was much less 

 than when these were united at the centre. They then experi- 

 mented on liquids by suspending a sphere or cylinder of the 

 liquid between the poles of a revolving electromagnet, and 

 succeeded in getting a decided and measurable eflect. The 

 importance of this is very great, for they have thus a means of 

 determining the conductivity of liquid electrolytes by currents 

 induced in the liquid without the use of electrodes, and without 

 polarisation. — Dr. Guthrie stated that as the push on the liquid is 

 directly proportional to the current quantity, they hope to 

 measure the conductivities of liquids, and connect these to the 

 conductivity of solids through the intervention of mercury. In 

 reply to Prof. Adams Mr. Boys said that the angle of deflection 

 of the conductor had proved to be proportional to its conducti- 

 vity. Dr. O. J. Lodge suggested that the conductivity of the disks 

 used in these experiments should be determined by plott ng out the 

 equipotential surfaces. Dr. Sylvanus Thomson recommended 

 trying conducting jellies in these experiments, and Dr. Guthrie 

 replied that such were being prepared for trial, includ ng the per- 

 manent jelly made by dissolving gelatine in anhydrous glycerine at 

 100°. — Prof. Sylvanus Thomson then communicated five laboratory 

 notes from University College, Bristol. The first related to the 

 source of sound in the Bell telephone receiver. Two theories 

 are now being discussed as to this t fleet, the molar theory regards 

 the motion of the diaphi-agm-mass as the source of sound, the 

 molecular theory finds it in the molecular motions of the mag- 



