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NATURE 



[May 4, 1905 



Geological and petrographical researches on the northern 

 Urals have for some years been carried on by Prof. Louis 

 Duparc and Dr. Francis Pearce. Their latest work {Mem. 

 Soc. de Physique et d'Hist. not. de Gin'eve, xxxiv., 

 fasc. V.) embraces a description of the eruptive rocks of 

 the chain of Tilai-Kanjaliowsky-C^r^briansky, in the 

 Government of Perm. This range is composed of basic 

 igneous rocks, of pyroxenites passing into koswites, which 

 form the principal axis of the chain, with bordering 

 gabbros elsewhere prominent ; there are diorites, norites 

 which are intercalated locally in both gabbros and 

 pyroxenites, and dunites which are massive in places and 

 also send veins into the gabbros and pyroxenites ; and there 

 are other eruptive rocks. All these are described in con- 

 siderable detail and illustrated. Continuing their observ- 

 ations eastwards, the authors describe the quartzites and 

 crystalline conglomerates of Aslianka and of T^pil, with, 

 in the latter region, Devonian strata and various igneous 

 rocks ; and finally they deal with the crystalline schists 

 and intrusive rocks of Koswinsky-Kat6chersky-Tilai. 

 The memoir is illustrated by pictorial views of the topo- 

 graphic features, by longitudinal sections, and by micro- 

 scopic sections of the rocks. 



The report of the ob.servatory department of the National 

 Physical Laboratory for the year 1904 shows, as usual, a 

 large amount of useful work ; it is published separately, as 

 appealing to a different class of workers from that interested 

 in the engineering and physics departments. The work of 

 the observatory deals with magnetic, meteorological, and 

 seismological observations (separately), experiments and 

 researches, verification of instruments and watches 

 (separately), and miscellaneous commissions for inland, 

 colonial, and foreign institutions, &c. It is observed that 

 the electric trams have interfered with part of the magnetic 

 work; the mean declination for the year was 16° 37'-9 W. 

 The tabulations and automatic records of the meteorological 

 observations are sent to the Meteorological Office for pub- 

 lication ■ in detail ; the Kew report contains monthly and 

 yearly summaries of the results. The seismological observ- 

 ations are published in the report of the British Associ- 

 ation ; the largest disturbance recorded during the year 

 took place on April 4, when the maximum amplitude ex- 

 ceeded 17 mm. The verification of instruments, exclusive 

 of watches and chronometers, amounted to 25,797, of 

 which 15,903 were clinical thermometers. 



During a thunderstorm it has often been noticed that 

 some flashes of lightning appear to " flicker," while others 

 seem to leave a glow in their paths which lasts a second 

 or two before entirely disappearing. In the first case the 

 apparent trembling of the light is due to the fact that the 

 observer is actually watching the passage of more than 

 one flash following the same route. In multiple or inter- 

 mittent lightning flashes there are sometimes as many as 

 live or six separate flashes in a very brief interval of time,' 

 and the impression on the retina is an apparent flickering 

 of a single flash. In the Comptes rendus (April 10) M. 

 Em. Touchet directs attention to those particular flashes 

 which leave a glow in their wake, and gives an illustration 

 of a photograph of one he secured with a moving camera 

 on April 12 of last year. The object of the communi- 

 cation is to point out that this glow is attributable to the 

 incandescence of the air ; but it seems to us that this is a 

 fact already very well known. In photographing very 

 bright lightning flashes with movable cameras it is a 

 very common occurrence to get trails on the plate of the 

 brighter portions of the flash, and if the plate and lens 

 be very rapid it should be the rule rather than the exception. 

 NO. 1853, VOL. 72] 



There are numerous examples of flashes which have been 

 photographed showing this peculiarity, and it is a simple 

 matter to differentiate between those due to multiplicity 

 and those due to the incandescent air resulting from the 

 original flash. .Anyone interested in this question vi'ill find 

 some typical photographs published by L. Weber (Si'fs. 

 d. fc. Preuss. Akad. d. Wiss., vol. xxxviii., 1889), Ladis- 

 laus von Szalay {Met. Zeit., vol. xxxviii., 1903, p. 341), and 

 B. Walter {Jahrhuch d. Hainburgischen Wiss. Anstalten, 

 vol. XX., 1903). As M. Touchet refers to Dr. Hoffert's^ 

 paper on intermittent lightning-flashes {Phil. Mag., 

 August, 1889), reference is there made to " streaks of 

 light, showing that a very considerable residual illumin- 

 ation remains between the discharges," which indicates, 

 that the writer was quite familiar with the incandescence 

 of the air due to the flash and its effect on the photo- 

 graphic film. 



An installation for the production of high-tension elec- 

 tricity, on view at Messrs. Isenthal and Co.'s, 85 Mortimer 

 Street, Cavendish Square, W., has been examined by a 

 representative of Nature. The original source of the 

 energy is an ordinary uni-directional current, and an im- 

 portant feature of the apparatus is a commutator which 

 does away with the necessity for an interrupter. In the 

 main circuit is a condenser of very large capacity, and the 

 commutator breaks the circuit when the condenser is 

 charged, so that no sparking is produced. The condenser 

 employed is not large, and owes its compactness to the ' 

 use of thin layers of aluminium o.xide, prepared electro- ' 

 lytically, as the dielectric. The commutator has the 

 appearance of a piece of engineering work, and should* 

 not require much attention. Oscillatory currents, with a 

 frequency of about a thousand per second, are set up in ■ 

 the primary of an induction coil, and it is claimed that the; 

 impulses in the secondary are much stronger in one direc- 

 tion than in the other. The apparatus is also intended for 

 the production of alternating currents, and some very 

 interesting experiments are shown. An alternating current 

 is sent through the coil of an electromagnet, the core being 

 vertical ; a sheet of paper is placed over the upper pole, and 

 on the paper is scattered some iron dust (not filings) ; the, 

 dust forms itself into little spiked heaps which move and 

 dance about. When the paper and iron dust are removed,, 

 and the forehead is placed near the pole of the magnet, the 

 light of the room appears to fluctuate in intensity. 



Messrs. A. Brown and Sons, Ltd., will publish during 

 this month a work by Mr. J. R. Mortimer entitled " Forty 

 Years' Researches in British and Sa.xon Burial Mounds of 

 East Yorkshire, including Romano-British Discoveries and 

 a Description of the Ancient Entrenchments on a Section of 

 the Yorkshire Wolds." 



The report of the council of the Hampstead Scientific 

 Society and the proceedings for 1904 have been received. 

 Fifty-six new members were elected during the year, and 

 the number of members is now 333. The number of 

 meetings held in 1904 was thirty-three, and in addition 

 there were four Christmas lectures to children and a course 

 of six lectures on nature-study. Among lectures delivered 

 at general meetings of the society may be mentioned one 

 by Prof. S. P. Thompson, F.R.S., on Japanese magic 

 mirrors, and one by Prof. W. Boyd Dawkins, F.R.S., on 

 the incoming of the Brythons into Britain. 



Messrs. S. Rentell and Co., Ltd., have published a 

 fifth edition of " The Telegraphists' Guide to the Depart- 

 mental and City and Guilds Examinations in Telegraphy," 

 by Messrs. lames Bell and S. Wilson. The contents have 



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