April 28, 192 i] 



NATURE 



269 



The Electrodeless Discharge in Sodium Vapour. 



By placing a primary Tesla coil about a highly 

 exhausted pyrex bulb containing metallic sodium, and 

 enclosing the whole in an oven, the writer has ob- 

 tained a brilliant electrodeless discharge at a tempera- 

 ture in the neighbourhood of 300° C. Observation 

 with a Hilger constant deviation spectroscope revealed, 

 in addition to the D lines, doublets at 6162 (and 6158), 

 at 5688 (and 5683), at 4667, at 4497, as well as faint 

 probable doublets at 5153, at 4980, and at 4572 — lines 

 all to be found in the arc spectrum. After two or 

 three hours' continuous heating the discharge was 

 almost as brilliant as initially, although the bulb on 

 removal from the oven had the usual brown colour 

 resulting from the action of the hot vapour. 



The writer has under way a further study of this 

 type of discharge with sodium and with other metallic 

 vapours, and hopes that with more violent excitation 

 than was used in the above case interesting spectro- 

 scopic data may be obtained. 



John K. Robertson. 



Queen's University, Kingston, Canada, 

 April 7. 



High-speed Aircraft Propellers and the Destruction of 

 Gnats. 



Some of your readers may be interested in an inci- 

 dent which took place during the testing of a propeller 

 at the Royal Aircraft Establishment, South Farn- 

 borough. The propeller was being revolved at a very 

 high speed, such that the tips of the blade were 

 moving at about 1000 ft. per second. The test was 

 carried out in the open, and the noise was such that 

 in the^ neighbourhood of the propeller it was impossible 

 to make oneself heard. Moreover, the noise gave an 

 unpleasant physiological sensation. The interesting 

 fact to your readers is that apparently this noise 

 attracted very large numbers of gnats, and most of 

 these lost their lives by being drawn through the 

 propeller, which on being stopped was found to be 

 covered with their blood and portions of their bodies. 



At the commencement of the test, and even _when 

 running with a tip-speed of 800 ft. per second," there 

 was no sign of any flying insects, nor was the dav 

 such that one would expect them. 



I have been present at many such tests, though 

 never at such a high speed, but I have not noticed 

 such an occurrence before. Henry C. Watts. 



April 21. 



Why do Worms Die? 



The Rev. H. Friend's letter in Nature of April 7 

 recalls an observation made towards the end of last 

 November with respect to the death of worms. .A 

 shallow gutter or water-drain by the side of a road 

 near Sidmouth had become filled with dead leaves 

 (principally of Populus alba) during the late autumn. 

 These by accumulation and pressure had formed a 

 firm, compact bed in the drain. During a night at 

 the end of November last we had exceptionallv heavy 

 rain, and the next morning, on passing along the road 

 in the forenoon, my attention was immediately 

 arrested by the number of \yorms (of several species) 

 lying dead outside the shallow water-drain. In the 

 space of about 20 ft. I counted upwards of a hundred 

 worms. They had evidentlv crawled out from the 

 bed of dead leaves to the firm surface of the road 

 and died there. Mv conclusion was that they had 

 crawled out from the gutter in a half-drowned condi- 

 tion and beyond the chance of recovery. A curious 

 point was that they all (irrespective of size and species) 

 appeared to have crawled to about the same distance, 

 so that they formed a fairly even line running parallel 

 with the gutter. G. T. Harris. 



NO. 2687, VOL. 107] 



Vegetation around London Earlier than in the Provinces. 



Nature of April 21, in the Notes columns, p. 245, 

 mentions that a correspondent who travels frequently 

 from the south-west of England to London finds at 

 this time of year vegetation, notably the flowering 

 trees, generally more advanced as the metropolis is 

 approached. In the past I have frequently noticed the 

 spring vegetation in London to be more forward than 

 thirty or forty «iiles outside. Commonly, in visiting 

 East Grinstead from London, I have noticed and re- 

 marked on the lateness of spring vegetation compared 

 with the metropolitan suburbs. This year at Tulse 

 Hill, and generally in the south of London, the pear- 

 and apple-trees were in fairly full blossom at the com- 

 mencement of March, whilst at Eastbourne similar 

 vegetation was fully three weeks later. The dates 

 from the Phenological Report for 1919 published by 

 the Royal Meteorological Society referred to in your 

 Note can scarcely claim to determine the general 

 difference between south-west and south-east England. 

 The early months of 1919 were abnormally cold and 

 wet, and on April 27 a snowstorm of considerable 

 severity occurred in the south of England. 



Chas. Harding. 



2 Bakewell Road, Eastbourne, April 21, 



A Modern Inorganic Chemistry. 



In a very able and courteous review of my "Text- 

 book of Inorganic Chemistry " which appeared in 

 Nature of April 14, "A. J. A." makes two statements 

 which I think might be misleading to many readers. 

 He states that " in practice calcium cyanamide is not 

 produced in an arc furnace." The Stockholms Super- 

 fosfat Fabriks Aktiebolag, Stockholm, make 20,000 

 tons of cyanamide annually in arc furnaces, and since 

 this modern so-called " continuous cyanamide process " 

 is referred to most respectfully in the report of the 

 Nitrogen Products Committee, I thought it worthy 

 of mention — in an imperfect manner, it is true. It 

 is quite possible that of the two cells described for 

 the manufacture of electrolytic alkali, one is "' obso- 

 lete " and the other "obsolescent." It is five years 

 since I saw one described in some text-books as 

 " quite obsolete " operating with great activity ; 

 doubtless it has now gone out of use. Since these 

 two cells, however, w«re the only ones I could find 

 authoritatively described as in use, or as having been 

 in use, in this country, I preferred to describe them 

 rather than cells existing only in patent specifications. 



J. R. Partington. 



My knowledge of the continuous cyanamide process 

 is confined to what appears in the Nitrogen Products 

 Committee's report, and I am afraid I did not know 

 that the preliminary heating of the carbide necessary 

 before it can absorb nitrogen was carried out by elec- 

 tric arc heating. The arc itself is, of course, at a 

 temperature far above that at which nitrogen can be 

 absorbed by carbide. 



With reference to Prof. Partington's second point, 

 there is nothing in his description of electrolytic 

 alkali cells to indicate that he is only dealing with 

 processes used in this country, and there is no lack 

 of authoritative descriptions of cells used abroad, 

 where electrolytic alkali has assumed greater im- 

 portance than has been the case here in the past. 

 Even so, I think I am right in saying that the 

 Castner-Kellner rocking cell is no longer used to 

 produce alkali for the market, and, this being so, 

 it appears a pity to devote to it such a dispropor- 

 tionate amount of attention. "Obsolescent" is, I 

 imagine, a fair description of the Hargreaves-Bird 

 cell. The Reviewer. 



