March 21, 1895J 



NA TURE 



493 



perimental evidence adduced in support of this view consisted 

 chiefly of the observation which he made that the pirent nitro- 

 I paraffin was not, or only to a slight extent, regenerated upon 

 treating the sodium compound with dilute sulphuric acid, the 

 I compound being decomposed with evolution of nitrous oxide and 

 ' formation of aa aldehyde or ketone. Prof. Meyer has made 

 further experiments in Ihii direction, and their results definitely 

 fix the nature of these sodium compounds, proving that they 

 are indeed true sodium derivatives of the nitro- paraffins, being 

 formed by the replacement of one of the hydrogen atoms of 

 the alkyl radicle by sodium. It is a fact that when sodium 

 nitro-ethane, CjHjNaNO,, is dissolved in excess of dilute sul- 

 phuric acid at the ordinary temperature, a somewhat vigorous 

 evolution of nitrous oxide occurs. But if the most elementary 

 precautions are taken to prevent the decomposition of so 

 unstable a substance by the thermal change involved in so 

 energetic a reaction, the decomposition proceeds quite dif- 

 ferently. If the sodium compound is first dissolved in a little 

 water well cooled by ice, .ind then an equivalent added of 

 dilute sulphuric acid similarly cooled to near o", only a very 

 few bubbles of gas escape, and barely a trace of the odour of 

 aldehyde is perceptible, while a layer of oil, consisting of nitro- 

 ethane, separates out. Even afier the operations of purification, 

 which involve some loss owing to the volatility of nitro ethane, 

 over 60 per cent, of the theoretical quantity of the pure nitro- 

 paraffin was isolated. Moreover, the small quantity ot decom- 

 position indicated by the few bubbles of nitrous oxide can be 

 entirely avoided by employing acetic instead of sulphuric acid ; 

 the reaction is then less vigorous, ani consequently produces at 

 temperatures not far above 0° no dissociation of the nitro- 

 paraffin. The observation of Nef, that the sodium derivatives 

 of the nitro-paraffins are decomposed at the ordinary tempera- 

 ture by the stronger acids, even when diluted, into nitrous oxide 

 and an aldehyde or ketone, is an interesting one ; but Prof. 

 Meyer's work now shows that this is due merely to the fact 

 that the nitro-paraffin first regenerated is decomposed in all 

 probability by the heat of the reaction between the sodium and 

 acid, and that when the precaution is taken to prevent this 

 rise of temperature by reacting with ice-cold solutions, the re- 

 generated nitro-paraffin remains intact. Hence it must be con- 

 cluded that the sodium compounds are true derivatives of the 

 nitro-paraffins which can thus be regenerated from them. 



The additions to the Zoological Society's Gardens durmg the 

 past week include a Vervet Monkey (Cercopithecus lalandii, 9 ) 

 from South Africa, presented by Captain Scarlett Vale ; a 

 Macaque Monkey {Macacus cynomolgus, i ) from India, pre- 

 sented by Miss K. Fleming ; a Vulpine Phalanger {Phalangista 

 vulpina) from Australia, presented by Mr. Richmond Allen ; 

 a Grey Ichneumon [HerpesUs griseus) from India, presented by 



Mrs. Lewis; fifteen KaXsi^Miis, sp. inc.) from Sunday 



Island, Kermadee Group, presented by the Countess of 

 Glasgow ; a Hooded Finch] (Sfierintsles CHCtdlata) from West 

 Africa, a Chestnut-eared Finch {Amadina castanotis) from 

 Australia, presented by Mr. C. II. Hastings ; a Woodcock 

 (Scolopax ruslicula), British, presented by Mr. Charles 

 Smoolhy ; a Long-necked Chelodine {Chelodina longicollis) 

 from Australia, deposited ; four Marbled Newts (Molge 

 marmoraia), European, purchased. 



OUIi ASTRONOMICAL COLUMN. 



Partiai, Eclipse uf the Sun, March 26. —On March 26 

 a small partial eclipse of the sun will, if the weather be favour- 

 able, be seen from all parts of the liritish Isles, with the pro- 

 bable ex;eption of places which are to the east of a line 

 joining Liwistift an 1 Ilistin^s. At Greenwich the magnitude 

 of the eclipse, sun's diameter = i, will hi 0013, and the first 

 contact will occur at 9 56 a.m., with a duration of only 27 



NO. 1325, VOL. 51] 



minutes. At Oxford the magnitude will be 003, and the 

 duration 40 minutes. At Dublin the magnitude will be O'og, 

 with a duration of 67 minutes, and at Edinburgh 008, with a 

 duration of 62 minutes. The eclipsed part will be a maximum 

 (o"36) as seen from the north-east of North America. 



In the Nautical Almanac for the current year the eclipse is 

 said to be invisible at Greenwich, but the error was corrected 

 \a\he Almanac for 1897. The mistake, however, has not been 

 corrected in many of the almanacs in common use. 



Distribution or Minor Planets. — An interesting dia- 

 gram has been constructed by General Parmenlier, to show 

 the distribution of the minor planets at present known between 

 the orbits of Mars and Jupiter (Bulletin Soc, Ast. de France, 

 March). jOf the 390 planets for which sufficient data are 

 available, 93 have a mean distance between 2"i6 and 2"4S; 

 152 between 252 and 2'82 ; 128 between 2'S5 and 3"25 ; and 

 10 between 3-38 and 3'48. The interval between Brucia (at 

 2'l6) and Mars, is occupied by a single asteroid, comparatively 

 recently discovered, with a mean distance of 2'09. On the 

 outer side of the dense swarm, there are only six minor planets 

 in a zone very nearly as wide as that occupied by the group of 

 383, and extending to a mean distance 4'68. The region of 

 greatest density of the asteroids so far discovered is at a mean 

 distance from the sun very nearly equal to that indicated by 

 Bode's law (2'8o) ; Ceres, Pallas, and Juno fall a little short of 

 this distance. 



At the present rapid rate of discovery of minor planets by 

 the photographic method, data will no doubt soon be available 

 to determine if the outer zone between Camilla and Jupiter is 

 really an almost deserted region. 



The Royal Observatory, Edinburgh.— We are glad to 

 hear that the new National Observatory for Scotland is making 

 rapid progress towards completion. The buildings are quite 

 finished so far as the outside is concerned, and it is hoped that 

 the two cquatorials and the transit instrument will be erected 

 in the early summer. The library will be ready to receive the 

 magnificent collection of twenty thousand volumes as soon as 

 the heating arrangements are completed. 



PHYSICAL WORK OF HERMANN VON 

 HELMHOLTZy 



II 



T/'ONIG has shown that in many cases, when two notes are 

 sounded simultaneously, beats are heard, as though t!ie most 

 prominent phenomenon was the production of beats not between 

 the two fundamental notes, but between the upper of these, and 

 the nearest partial of the lower note. Inasmuch as these beats are 

 heard when the lower note (as far as can be tested) is free from 

 upper partials, this rule is not the explanation of the pheno- 

 menon, but it is a convenient way of expressing the results. In 

 the experiment just described, the frequencies of the two notes 

 were in the ratio 12 to 15. The first partial of the lower note 

 (12) is therefore the nearest to the higher tone ; that is to say, 

 Konig's beat tone and the first difference tone are identical. 



It is easy to arrange an experiment in which these conditions 

 are not fulfilled. Thus let the notes be in the ratio 9 : 15. 

 The second partial of the lower note is 18, which is nearer to 15 

 than to 9 ; hence the Konig beat-tone would have a relative 

 frequency of 18-15 = 3. If the siren rotates io'6 times per 

 second, the frequencies of the two fundamental notes are 

 9 ;; 106 = 96 and 15 x io6 = l6o respectively. As before, the 

 difference tone is 64. 



In this case we can use another method of determining the 

 speed of the siren. In 1880 Lord Rayleigh constructed an 

 instrument in which the mass of air enclosed in a tube is 

 excited by resonance, and the fact of the excitation is indicated 

 by a light mirror, which is set where the motion is greatest, 

 inclined at 45" to the direction of the air-currents. In accord- 

 ance with the general law that a lamina tends to place 

 itself perpendicular to the direction of a stream, the mirror 

 moves when the air vibrates. In the original apparatus the 

 .amount of the movement was controlled by magnets. Since 

 that date Prof. Boys has modified the instrument by substitut- 

 ing a quartz thread suspension for a silk fibre, and using the 



^ A discourse delivered at the Royal Institution, by Prof. A. W. Riicker, 

 F.K.S., OD Friday, March S. (Continued from page 475.) 



