20 



NA TURH 



[May 3. 1900 



Search Ephemeris for Eros. — In view of preparing for 

 observations of this minor planet during the coming opposition, 

 the following ephemeris has been prepared by J. B. Westhaver 

 from the elements computed by H. N. Russell {Astronomical 

 Journal, No. 479, vol. xx. p. 185). 



Time. 



May 3 ... 23 2 o-i ... -4 o 25 ... 13-4 



1 3 -.3 



[3-2 



13-2 



13' 



13-0 



Relation between Solar Activity and Earth's 

 Motion. — In the Astronomische Nachrichten (Bd. 152, No. 

 3635), Mr. W. G. Thackeray criticises the recent paper by Dr. J. 

 Halm {Astr. Nach. Bd. 151, No. 3619, Nature, March 8, p. 445), 

 deducing certain relations between the sun-spot cycle, the 

 changes in the obliquity of the ecliptic and the variations of the 

 terrestrial latitude. Mr. Thackeray states first, that continuous ob- 

 servations of sun spots have only been made since 1 825, so that the 

 sixty years period lacks sufficient evidence ; secondly, that Dr. 

 Halm has ignored some of the systematic errors of observation, 

 particularly those depending on the corrections for temperature in 

 the transit circle reductions, although in some cases their 

 amount affects the value of the obliquity by as great a quantity 

 as the whole amplitude of Chandler's long period inequality of 

 latitude variation. The paper includes a table showing the 

 annual corrections to Leverrier's obliquity from 1836-1896, with 

 corresponding yearly means of Wolf's spot numbers. These 

 differ from the values adopted by Dr. Halm, and the resulting 

 plotted curves show little or no resemblance. 



Determination of Solar Parallax from Opposition 

 of Eros. — In the Astronomical lournal i^o. 480, vol. xx. pp. 

 189-191), Prof. S. Newcomb directs attention to the favourable 

 opportunity for determining the Solar Parallax which will be 

 afforded by the comimg opposition of the minor planet Eros, in 

 December 1900, the conditions being conducive to more accurate 

 direct measurements than have ever before been presented. As 

 another such favourable opportunity will not occur for more than 

 thirty years, several suggestions are made for determining the 

 best combination of observations. 



The period during which determinations may be made is 

 remarkably long, as during the five months from 1900 Octo- 

 ber 15 to 1901 March 15, the distance of the planet will be less 

 than 0"50 astronomical unit. 



The high degree of precision attainable in late years by photo- 

 graphy indicates this as the best method, an additional point in 

 favour of this plan being that photographic telescopes are already 

 in use at various stations, and need only devoting to this work. 

 In arranging the programme of observations three objects should 

 be kept in view : — 



, First, the station and hours of exposure should be so chosen 

 as to secure the maximum of parallactic angles. 



Secondly, endeavour should be made to secure simultaneous 

 exposures at different stations, in order to lessen the uncertain- 

 ties arising from differences of scale, changes in relative position 

 of planet among stars, and in the reduction of the position of 

 the planet from hour to hour. Series of independent determina- 

 tions should also be made, each within an interval of twenty-four 

 hours. 



Thirdly, the relative displacement should, as nearly as 

 possible, be in a direction at right angles to the motion of the 

 planet among the stars. 



Prof. Newcomb then describes four charts included in the 

 paper, showing projections of the earth as seen from Eros at the 

 Epochs (1) middle of October to end of November ; (2) about 

 December 16 ; (3) about January 10 ; (4) about February 1. 

 On these are marked the sunset and sunrise lines, and paralUels 



NO. 1592, VOL. 62] 



of latitude corresponding to the principal observatories : Hel- 

 singfors, Pulkowa, 60° lat. ; Greenwich, Paris, Potsdam, &c., 

 50° lat. ; Jamaica, Madras, 15° lat. ; Arequipa, - 15° lat. ; 

 Cape of Good Hope, - 35° lat. On these projections the 

 direction of the planet's motion for different dates is indicated, 

 so that observers may find by inspection the relative importance 

 of observations at various stations and at various times of 

 night. 



Respecting the degree of precision it may be possible to 

 attain in the final result, it is noticeable that the course of the 

 planet throughout the entire period will lie along the borders 

 of the Milky Way, ensuring more and nearer comparison-stars 

 than would otherwise be available. An element of uncertainty 

 is the probable error of measurement from the plates. From a 

 consideration' of Kapteyn's investigation of the Helsingfors 

 parallax plates, and those at Potsdam, it is likely that the 

 probable error of the solar parallax from a pair of simultaneous 

 plates at Arequipa and Helsingfors would be +o"'02, and even 

 this might be reduced were it not for the uncertainty arising 

 from the motion of the planet. 



WORKING SILICA IN THE OXY-GAS 

 BLOWPIPE FLAME. 

 'T'HE plastic state of silica, and the elasticity of fine threads of 

 *- vitreous silica, were first observed by M. Gaudin (Comptes 

 rendus, viii. 678, 711) in 1839; but his observations seem to 

 have attracted but little attention, and the valuable qualities of 

 " quartz threads " remained unutilised till they were independ- 

 ently rediscovered and applied by Prof. C. V. Boys in 1887. 



Similarly, M. A. Gautier succeeded, in 1869, in making very 

 narrow tubes of silica, and showed such tubes in Paris in the 

 year 1878, but he failed to make further progress, even with the 

 aid of M. Moissan's electric furnace {Comptes rendus, cxxx. 816, 

 March 26), and his early work was so completely forgotten, both 

 in France and England, that the latest French worker on the 

 subject, M. A. Dufour, was evidently unaware of its existence a 

 few weeks ago {Comptes rendus, cxxx. 775, March 19). 



But though it thus appears that Prof. Boys was not, as has 

 been supposed, actually the first physicist to draw silica into 

 threads, or work it into fine tubes, there can be no doubt but 

 that his observations, methods of working and experiments have 

 formed the basis of all that has been done since the publication 

 of his first paper in 1887. 



In June 1899, one of the authors of this article exhibited (in 

 conjunction with W. T. Evans), at the Royal Society's Soiree, a 

 tube of vitreous silica, about 12 cm. in length and i cm. in 

 diameter, and at the same time showed the process by which it 

 had been made. Since that date we, the present writers, have 

 made a good deal of further progress. We have succeeded in 

 making longer tubes of various thicknesses, and in joining such 

 tubes both end to end and at right angles. On February 22, we 

 filled and sealed an ungraduated mercury thermometer made 

 entirely of vitreous silica ' ; and what is equally important, we 

 have entirely overcome the difficulty caused by the great tendency 

 of quartz to splinter when suddenly thrust into the oxy-gas flame. 

 We therefore now publish a short account of our methods in the 

 hope that they may enable others to take advantage of the new 

 material without undertaking a tedious preliminary investigation 

 into its properties and the methods of working it. We may 

 perhaps be permitted to add that we have already commehced 

 experiments intended to test the suitability of silica for use in 

 mercury and air thermometers, especially in regard to the fixity, 

 or otherwise of their zero points, that M. A. Dufour is engaged 

 on similar work, especially in relation to high temperature ther- 

 mometers, and that we are also studying the fitness of silica 

 apparatus for researches on the properties of pure gases.^ 



To prepare Non-splintering Silica. — The best form of silica 

 for use before the blowpipe is rock crystal. This may be ob- 

 tained in the form of chippings, or in masses which have proved 

 unsuitable for optical work. We have experimented with the 

 lighter particles of Kieselguhr, after well washing them with 

 strong hydrochloric acid, and also with well-washed precipitated 

 silica ; but, though these can be worked before the blowpipe 

 without much difficulty, they have not proved satisfactory in our 

 hands, as they yield an opaque product which is only suitable for 

 a few purposes. 



1 Nature, April 5, p. 540. 



- This will obviously involve a careful investigation into its power of 

 condensing gases and vapours. 



