Dec. 12, 1889] 



NATURE 



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is probable, Mr. Burnham's remeasurements after eleven 

 years indicatingrelative fixity,notwithstandingAldebaran's 

 appreciable advance in the meantime. A more remote 

 companion, however, discovered by Herschel in 1781, is 

 certainly optical, and has been shown at Lick to be double 

 {ibid., No. 2875). Most likely it forms part of the cluster 

 of the Hyades, upon which Aldebaran is casually projected. 



The division of the leading member of the group 

 known as o- Ononis illustrates Struve's remark that 

 multiple stars are intermediate between double stars and 

 clusters. Herschel saw it as doubly triple, one set being 

 much fainter than the other. Each proved, under Struve's 

 and Barlow's scrutiny, quadruple, with two very small stars 

 between ; while the chief of the decuple assemblage has 

 been resolved at Lick into an excessively close pair, re- 

 calling the case of Sir J. Herschel's quintuple star 45 

 Leporis, broken up into nine components by Burnham in 

 1874. No relative, and scarcely any absolute motion is 

 perceptible among the constituents of o- Orionis ; but one 

 of them, called " ashen " by Strove, " grape-red " by Webb, 

 is perhaps variable in colour. 



The " Pointer " next the Pole, a Ursae Majoris, has 

 so far been seen as double only with the giant telescope 

 of Mount Hamilton. The extreme difficulty of the pair 

 arises from the disparity of light between its members, 

 the eleventh magnitude satellite at o"'83 being almost 

 swallowed up in the glare of its brilliant primary. This 

 disparity, too, throws some shadow of doubt on the reality 

 of the connection, since the supply of small stars for the 

 occupation of chance positions is of course vastly greater 

 than of large. The similar, but more distant companion 

 of y CassiopeicC (at 2""i8) also recently discovered at 

 Lick, is hence not unlikely to prove merely optical, the 

 Milky Way, in which this pair occurs, being pre-eminently 

 rich in such objects ; and the presumption is still smaller 

 that a fourteenth magnitude neighbour of 6 Cygni owns a 

 genuine allegiance. But here, as Mr. Burnham points 

 out, the proper motion of the larger star will speedily 

 decide {Astr. Nach., No. 2912.) There can, on the other 

 hand, be no hesitation in admitting that i] Ophiuchi, re- 

 solved last spring by the same indefatigable observer into 

 two nearly equal components, at o""35, constitutes a physical 

 system, and one in which rapid movements may be looked 

 for. The stars evidently travel together, else they should 

 have been, through the effects of a proper motion of one 

 second of arc in ten years, so far apart a little time back 

 that they could not possibly have escaped separate dis- 

 cernment. Their relation to the Milky Way is picturesque, 

 and has been thought to be significant. " Situated at the 

 extreme northern and pointed extremity of a luminous 

 elongated patch of milky light," Mr. Gore remarks, j? 

 Ophiuchi '' looks as if it were drawing the nebulous matter 

 after it like the tail of a comet " {Journal Liverpool Astr. 

 Society, vol. vii. p. 178). But we may safely regard the 

 appearance as illusory. 



Some of Mr. Burnham's measures of known doubles 

 also supply results of interest. Thus, the duplex, sea- 

 green companion of y Andromedce can now barely be 

 *' elongated" with a magnifying power of 2700 on the 

 great refractor. Yet, so lately as i38i, the two stars could 

 be distinguished with eight inches of aperture. The un- 

 equal pair, 99 Herculis, discovered by Alvan Clark in 

 1859, is even more recalcitrant. No amount of optical 

 •constraint can now extract from it the slightest indication 

 of duplicity. Since 1878, 85 Pegasi has traversed 213° of 

 its orbit ; and Mr. Schaeberle's new elements, embodying 

 the Lick data, give it a period of 12I years, and oblige 

 us (on the dubious assumption that Briinnow's small 

 parallax can be depended upon) to ascribe a mass to the 

 system eleven times the solar, the components revolving 

 at nearly eighteen times the distance of the earth from 

 the sun. The sun and Jupiter, if of equal ureal lustre, 

 would present, at half the supposed distance of 85 Pegasi, 

 just its telescopic aspect. 



Like 85 Pegasi, 8 Equulei is optically triple, while 

 physically double, the companionship of Struve's more 

 distant attendant being in each case temporary and acci- 

 dental. The bright star of S Equulei was divided by 

 O. .Struve in 1852, and the pair soon proved to be in 

 exceptionally rapid motion. They constitute, in fact, the 

 swiftest binary system yet known. Glasenapp's period, 

 nevertheless, of iii years is evidently too short. The 

 Lick measures show the star to be lagging slightly behind 

 its predicted place. 



The investigation of stellar orbits has scarcely yet 

 emerged from a tentative stage. Its results are for the 

 most part loose approximations, largely open to future 

 correction. There are very few stars of which the period 

 is known within a few years ; there are perhaps two — 42 

 Comas and ^ L^rsa; — of which it is known within a few 

 months. This is due to no lack of skill or diligence in 

 the computers, but solely to the deficiencies, both in quality 

 and quantity, of the materials at their command. Very 

 small errors become enormous when they affect the relative 

 situations of objects divided by a mere hair-breadth 

 of sky ; and there is no branch of astronomy in which 

 " personality " has played a more conspicuous or a more 

 vexatious part than in double-star measurements. This at 

 least is abolished by photography ; which has, however, as 

 yet proved applicable only to a limited class of coupled 

 stars. With the extension of its powers to all, a new 

 era in the knowledge of stellar revolutions may be ex- 

 pected to open. 



A. M. Clerke. 



GEOLOGICAL EXCURSION TO THE ACTIVE 

 AND EXTINCT VOLCANOES OF SOUTHERN 

 ITALY. 



nPHE excursion of geologists to the volcanic regions 

 -*■ of South Italy came to a very satisfactory con- 

 clusion. We have already referred to the first part of 

 the excursion to the Lipari Islands, and the interesting 

 state of activity in which the volcanoes of Vulcano and 

 Stromboli were found to be in. On leaving those islands 

 the party proceeded to examine the Val di Bove, the 

 Cyclopean Islands, the slopes of Etna with its numerous 

 parasitic cones and lava streams, and the central crater 

 itself The Italian Minister of Public Instruction allowed 

 the party to sleep in the observatory near the mountain 

 summit, and although the weather was rough and misty, 

 about half the party were able to get a good view of the 

 crater, which is now in a solfataric condition. The 

 geologists had also the advantage of becoming acquainted 

 with the mud volcanoes of Paterno. In this part of the 

 excursion the party had the valuble help of Prof O. 

 Silvestri, to whom Dr. Johnston-Lavis handed over the 

 direction at Etna, although still acting as general director 

 and interpreting Prof Silvestri's demonstrations. All 

 along the journey the party were feted by the prefect 

 of the province and the mayors of the different com- 

 munes, and found invaluable hospitality in the splendid 

 villa of the Marquis Favara at Biancavilla. The second 

 fortnight of the excursion was spent at Naples and 

 its vicinity, under the direction of Dr. Johnston-Lavis, 

 aided for the sedimentary ro:ks by Prof Bassani of the 

 University of Naples. Although the weather was not so 

 favourable as in Sicily, the delay only amounted to two 

 days. Many thanks are due to the mayor of Naples for 

 his hospitality in providing for the party a splendid steam 

 yacht for their visit to Capri and Ischia, so affording very 

 greatly increased facilities for their excursions. The 

 members gave a day to the examination of the reservoirs 

 and other works connected with the new and most perfect 

 and purest town water supply in Europe, as well as the 

 new drainage works and destruction of the old town of 

 Naples. Although the visit to the crater of Vesuvius had 

 to be delayed for upwards of ten days for suitable weather, 



