io3 



NA TURE 



[November 30, 1893 



force took place until May 31. This and the following day 

 were visited by two considerable shocks, followed by another 

 strong concussion on June 5, which marked the close of the 

 eccentric eruption. The 9th witnessed some disturbances ac- 

 companying a mild eruption of the central crater, and calm was 

 tiuJ.Iy re-established on June 14. A coincidence worth noticing 

 is tha-. of the highest barometric pressure observed during all 

 that time, a pressure of 771 mm., with that of the great central 

 eruption on May 18. The greatest disturbances were pro- 

 duced along a line passing through the focus in a direction from 

 east-north-east to west-south-west, this being at right angles 

 to a radial line which was the seat of the 1883 eruption. 



Measurements of the amount of light absorbed by thin me- 

 tallic films of various thicknesses are incapable of affording a true 

 measure of the absorptive power of these films unless the films 

 compared have the same reflecting power at normal incidence. 

 M. Salvador Bloch has been for some time experimenting with 

 collodion films coloured with fuchsine, and thus made to exhibit a 

 metallic aspect. According to an account published in the 

 CovipUi RendiiSf he has succeeded in obtaining films of different 

 thicknesses and of equal reflecting powers. Two pellicles formed 

 by pouting layers of different thickness over glass plates, and 

 evaporating under the same conditions, show, if all goes well, 

 a strong resemblance as to reflecting powers. This wasUested 

 by studying with a Babinet compensator the ellipticity of the 

 green rays near the E line reflected from the pellicle. The 

 employment of sunlight enabled the observer to measure 

 differences of phase down to oj^ of a wave-length. For 

 two such pellicles no difference of phase exceeding or even 

 approaching that limit was observed in any portion of the films. 

 Three such films, called A, B, and C, and of thicknesses ; 744, 

 1921, and 1964^^1, respectively, were used for determining the 

 index of absorption for the yellow D rays. The index of ab- 

 sorption was taken as defined by the fact that a vibration 



progressing in the absorbing medium through a length — has 



27r 



its amplitude reduced in the ratio i : e~y, where 7 is the index 

 of absorption. From A and C combined, •> was found to be 

 o"o88, and from A and B o"oS4. Films of such thickness were 

 opaque to green, but another set of films, of thicknesses 353, 

 504, and 627ujLt, respectively, were found thin enough for mea- 

 surements in the case of green light. The two corresponding 

 values found were o'529 and 0'505. The spectrophotometer 

 used was analogous to a half shadow polarimeter. A polarised 

 beam of sunlight fell normally upon a biquartz. The light then 

 passed through an analyser with divided circle, and then through 

 a lens, which projected an image of the biquartz upon the slit 

 of a spectroscope provided with an eye-slit. The spectrum then 

 consisted of two superposed portions, each corresponding to one 

 of the quartz plates. The_film was then cut half off the 'glass, 

 and placed so that the edge coincided with the junction of the 

 biquartz, with the result that the light suffering absorption 

 passed through one of the quartzes only. Equality was estab- 

 lished by turning the analyser. A special advantage of this 

 arrangement is that it requires only one source of light. - '• ^ 



There exist at present numerous arrangements for "turning 

 down" an electric light, the chief peculiarity of them all being 

 that nearly as much electrical energy is consumed when the 

 lamp is only glowing feebly as when it is giving its normal 

 amount of light. An arrangement to which this objection does 

 not apply is described in the Proceedings of the American 

 Institute of Electrical Engineers for September, by Mr. F. 

 Moore. In the circuit of the lamp there is placed an automatic 

 interrupter, consisting of a small electromagnet and an armature 

 held back by a spring ; the contacts being so arranged that as 

 the armature vibrates the current is interrupted during part of 

 NO. 1257, VOL. 49] 



the oscillation. By this means different amounts of current can 

 be passed through the lamp, for by moving the electromagnet 

 nearer to or further from the armature, the speed with which 

 the latter vibrates can be varied. To avoid the destructive 

 effect of the sparks at the contacts the whole armature is 

 enclosed in a glass globe from which the air has been ex- 

 hausted. Under these conditions it is found that platinum 

 contacts remain good for a considerable time. When the inter- 

 rupter is at work the sparks produce in the exhausted globe a 

 phosphorescent glow which the author thinks may possibly be 

 made use of for the purpose of giving light. Another applica- 

 tion of the above is for running lamps on circuits of much higher 

 voltage than they are intended for. 



Wiedemann ^ Annalen der Physik und Chcmie for November 

 contains an interesting paper by R. Hennig, on the magnetic 

 susceptibility of oxygen. The method employed, namely, the 

 measurement of the displacement in a magnetic field of a short 

 column of liquid in a slightly inclined capillary tube, due to the 

 difference in the susceptibility of the two gases (oxygen and air) 

 at the two ends of the liquid column, would hardly seem at first 

 sight capable of giving very accurate values. The author, how- 

 ever, has obtained very fairly consistent results, and finds the 

 value 0'0963 x 10"'' for the difference between the susceptibility 

 of oxygen and air at a temperature of about 26"' C, and at 

 pressures varying from 75 cm. of mercury to 328 cm. lu order 

 to measure the strength of the magnetic field a small coil was 

 suspended by a bifilar-suspension close to the capillary tube, 

 and from the deflection, when a known current was passed 

 through this coil, the strength of the field was calculated. The 

 results obtained by this method were also compared with those 

 found by the rotation of polarised light in a piece of heavy 

 glass, and by means of a small induction coil which could be 

 rapidly moved out of the field. 



Some interesting investigations on the vitality of the cholera 

 organisms on tobacco have been made by Wernicke {Hygien : 

 Rtindschau, 1892, No. 21). Small pieces of linen soaked in 

 cholera broth-cultures were rolled up in various kinds of tobacco, 

 and the latter made into cigars. At the end of twenty-four hours 

 only a few bacilli were found on the linen, and none on the leaf. 

 On sterile and dry tobacco leaves, the bacilli disappeared in one- 

 half to three hours after inoculation. On moist, unsterilised 

 leaves they disappeared in from one to three days, but on moist 

 and sterile leaves in from two to four days. When introduced 

 into a five per cent, tobacco infusion (10 grams of leaves to 200 

 grams of water), however, they retained their vitality up to 

 thirty-three days ; but in a more concentrated infusion (one 

 gram of leaves to two grams of water, they succumbed in 

 twenty-four hours. When enveloped in tobacco smoke, they 

 were destroyed, both in broth-cultures as well as in sterilised and 

 unsterilised saliva, in five minutes. Tassinari, in his paper, 

 "Azione del fumo di tabacco sopra alcuni microrganismi 

 patogeni " (/^;^«a/^ deli Istituto d'Igiene, Rome, vol. i., 1891), 

 describes a series of experiments in which he prepared broth- 

 cultures of different pathogenic microbes, and conducted through 

 them the smoke from various kinds of tobacco. Out of twenty- 

 three separate investigations, in only three were the cholera 

 organisms alive after thirty minutes' exposure to tobacco fumes. 

 But in actual experience the apparent antiseptic properties of 

 tobacco have not unfrequently been met with ; thus, during the 

 influenza epidemic in 1889, Visalli {Gazetta degli Ospedali, 1889) 

 mentions the remarkable immunity from this disease which 

 characterised the operatives in tobacco manufactories ; that in 

 Genoa, for example, out of 1 200 workpeople thus engaged, not one 

 was attacked ; whilst in Rome the number was so insignificant 

 that the works were never stopped, and no precautions were 

 considered necessary. 



