Dec. 17, 1885] 



NATURE 



153 



been watched here witliout indication of an associated star- 

 shower. Still, the circumstance that certain meteoric displays 

 have occurred contemporaneously with other phenomena, is in- 

 teresting (though not, perhaps, significant, as intimating any 

 physical connection), and such records should always be pre- 

 served, as possibly having a value which further observations 

 may elucidate. 



During the great meteoric shower of November 13, 1866, 

 several observers detected a faint diffused light of an auroral 

 character in the northern sky. 



In 18S0 there were bright displays of aurorse on August 11, 

 12, and 13. Whilst watching the Per,-eid meteor-shower on 

 those nights, I noticed the successive appearances of streamers 

 and light condensations in the northern quadrant. On the 13th 

 the sky was much lighter than usual, though no streamers or 

 bright glows were visible. The moon set before loh., yet at 

 midnight the air was not dark ; objects around were discernible 

 with remarkable facility beneath the luminous gauze of the 

 aurora apparently diffused over the sky. 



During the present month I have been engaged in a series of 

 observations of the Geminid meteor-shower. On December 7, 

 8, 9, and 10. I especially noticed singular light-radiations, like 

 broad films of faint white cloud, in the northern region. These 

 were very striking on December 9, and persistent during several 

 hours. The most conspicuous of these radiations stretched out 

 of the horizon in the north-north-east, and ran obliquely a con- 

 siderable distance east, where it enveloped the stars of Virgo and 

 Leo. The effect was somewhat similar to that of the zodiacal 

 light, but in the present case the phenomenon had an evident 

 tendency to remain in the vicinity of the horizon. On its upper 

 side I distinguished very faint indications of streamers, with 

 alternating spaces rendered very dark by contrast. The appear- 

 ances were, however, so constant, that they can hardly be 

 associated with the characteristic mobile forms of ordinary 

 aurorje. The sky generally was very light, and I have specially 

 noticed this fact on several other occasions this month, when an 

 observer miglit readily have assumed that the moon, in one of 

 her quarters, was present in the firmament. 



A suffused glowing of the whole sky such as that now re- 

 corded has not infrequently been visible here in past years during 

 the progress of meteoric observations. Though no definite 

 aurorfe (in its normal features) can be descried, there is ob- 

 viously some modification often present imparting to the 

 finnament those peculiarities of aspect and tint which are far 

 too striking to escape notice. I believe that scarcely a very 

 clear night passes but there may be traced, with a critical eye, 

 some feeble traces of aurorce, or their closely-allied phenomena. 

 Could these ever-varying sky-tints be studied in a fine climate, 

 I feel assured we might look for some interesting results. 



Bristol, December 12 W. F. Denning 



The Supposed Fall of an Aerolite in Naples 

 The late beautiful meteoric display, which was well seen here, 

 has given rise to a somewhat ludicrous incident. The local 

 papers on Sunday evening and Monday contained an account of 

 an aerolite that had fallen in the Strada Fiorentino, one of the 

 principal thoroughfares of the town ; that this stone weighed 

 between 6 and 7 kilogrammes, and had nearly struck some people 

 who were passing. This announcement was followed by a 

 description of the stone from the pen of one of the professors in 

 the University, together with an account of meteorites in 

 general. 



Such a display of erudition, coinciding with the bombardment 

 our earth has had from Biela's comet, prevented my sleeping all 

 night, and, as early as etiquette would allow, I paid a visit to 

 the house of the two professors, the happy (?) possessors of this 

 would-be aerolite. The first examination convinced me that we 

 had to deal with a shoemaker's lapstone of Vesuvian lava, the 

 patina being nothing more than the polish of grease, dirt, with 

 wear and tear. A small fragment was given me, which, after 

 being sectionised, showed a typical leucitophyre of Vesuvius — 

 probably the lava of 1631 from " La Scala " quarries. 



I should not have written to you had it not been that such 

 confirmation had been given by men of position, whom I 

 have now obliged to admit their mistake. Probably, however, 

 the report of the fall of this supposed aerolite has already spread, 

 so that I fear it may be included in lists of historic meteorites. 



I may say that the stone had probably fallen or been thrown 

 from one of the roofs of the neighbouring high houses. 



December 9 H. J. Johnston-Lavis 



The Rotation-Period of Mars 



In the number of Nature of November 26 (p. 81), Mr. 

 Proctor mentions one or two points in my investigation of the 

 rotation-period of Mars, requiring correction. 



The first is, that I did not use Proctor's final result for the 

 period, but one which he published in 1869, differing 0'02s. 

 from the former. As I intended to determine from the whole 

 series of Mars's drawings the correction of the rotation-period, 

 it was perfectly indifferent what value I adopted in my calcula- 

 tions ; the only condition was, the error should not be so great 

 as to cause an erroneous interpretation of the Mars pictures of 

 former years. A difference of o'02s. in the adopted rotation- 

 period changes the position of the markings in the drawings of 

 Huygens and Hook but 2''-9, so that for my purpose I could 

 adopt Proctor's value of 1869 as well as that of 1873. I chose 

 the former, as it seemed, after a preliminary reduction of 

 Schrffiter's observations, to be nearer the truth ; but my results 

 would have been absolutely the same had I chosen the second. 



The second remark of Mr. Proctor's is the following : — " Prof. 

 Backhuyzen, like Mr. Denning some time since, has taken 

 Kaiser's result uncorrected for the clerical errors — very seriously 

 affecting it— which I detected in 1873." As I have used only 

 Kaiser's original observations, and no result whatever, corrected 

 or uncorrected, I must conclude that Mr. Proctor has not read 

 my paper very accurately ; when he does so, he will see that he 

 is wrong. At the same time he can see that on p. 58 the time 

 of Hook's observations is given, " March 12, I2h. 20m. and 

 I2h. 30m.," and from the indication on p. 55, that there is an 

 integral number of revolution -periods of 24h. 37m. 2274s. 

 between 1862, November i, 9h. 55m. mean time Berlin, and 

 1672, January I, 22h. ii-om. mean time Paris, he may conclude, 

 after a slight calculation, that I did not count the years 1700 

 and iSoo as leap-years. My results are, therefore, free from 

 the errors Mr. Proctor indicated ; I hope I made no other. 



It seems, however, very difficult to avoid them wholly. Mr. 

 Proctor, for instance, who occupied himself so much with the 

 subject, writes, in the above-mentioned number of Nature of 

 November 26 : "Kaiser counts three days too many in compar- 

 ing Hook's observation with his own : one day, through a 

 mistake in correcting for change of style and two days (ap- 

 parently) from counting the years 1700 and 1800 as leap-years." 

 That number of three days must be one day, for Kaiser indicated 

 as the time of Hook's observations, March 13, I2h. 20m. new 

 style, instead of March 12 ; by this error the number of days 

 from 1862, November i, till Hook was one day too small ; 

 but, by counting 1700 and 1800 as leap-years. Kaiser added two 

 days too many, so that the total error was one day, and not 

 three. Mr. Proctor's conclusions, based on the latter assump- 

 tion, are naturally erroneous. 



H. G. Van de Sande Bakhuyzen 



Leyden Observatory, December 9 



In Nature for December 10 (p. 132} I note the suggestion : 

 — " In all new buildings where efficient ventilation is desired, 

 it would be preferable to construct a shaft at one side of, or 

 surrounding the chimney-flue, with an inlet near the ceiling of 

 the room, and the outlet at the level of the chimney-top, so 

 that the air escaping from the room would have its temperature 

 kept up by contact with the chimney, thus aiding the up-draught, 

 whilst the risk of reflux of smoke would be avoided." In 

 building my own house some eight years ago this system was 

 adopted in every room, the outlet over the chandelier being 

 carried across to the side of the chimney of the same room, 

 the two flues being carried up side by side to the chimney 

 stack, each outlet having its own cowl. In practice this has 

 proved a total failure, from the simple fact that the fire-flue 

 is both longer, owing to its starting at a lower level, and that 

 it is also hotter than the other. In the absence of any fire 

 there is a strong upward current in both, but the instant the fire is 

 lighted the upward current in the ceiling ventilator stops, and in 

 a few minutes is reversed, the cold air and collected smoke from 

 the chimney outlet coming in with such force that we have 

 been compelled to make up every ceiling ventilator in the house 

 except one, which, although useless when a fire is lighted, is 

 not a nuisance. Many other experiments in automatic ventila- 

 tion were tried, so that in case one system failed others might 

 be available, and I regret to say that the only useful remnant of 

 the experiment is the ventilation from the entrance hall, which 



