;78 



NJi TURE 



[January 27, 1910 



U\]R ASTRONOMICAL COLUMN. 



Halley's Comet, igogc. — A further extract from Mr. 



Crommelin's corrected ephemeris (Astronomische Nach- 



richten, No. 437g, p. 170) for Halley's comet is given 



below : — 



Ephemeris for Greenwich Noon. 

 R.A. Decl. log >■ 



log A 



oigi6 



0'i473 



o 'og? I 



0-2284 

 02410 

 02522 

 0'26i7 

 0-2688 

 0-2743 

 02774 



+ 8 27 

 + 8 14 

 + 84 

 + 7 58 

 •<- 7 55 

 + 7 54 

 + 7 55 



These positions will be found plotted on the chart which 

 we gave in our issue for January 13, p. 320, and it will 

 be seen that the comet is now apparently travelling slowly 

 westwards through the constellation Pisces ; on February ^ 

 it win be nearly 1° north of the 4-5 magnitude star 

 6 Piscium. During February the comet's distance from 

 the sun will decrease from about 151 to 108-7 million 

 miles, whilst the distance from the earth will increase from 

 about 157 to 176 million miles. According to the 

 ephemeris given by Prof. Searle in No. 607 of the Astro- 

 iiomical Journal, the brightness should, during February, 

 increase from 20 to 30, the unit taken being the bright- 

 ness on September 11 when re-discovered. In the same 

 journal Prof. Barnard gives some further observations, 

 and states that on December 7 the comet was an easv 

 object, appearing to have a small nucleus, in the 4-inch 

 finder of the 40-inch telescope. In the latter it appeared 

 much larger, and its magnitude was about 10-5. 



In No. 4383 of tlie Astronomische Nachrichten (p. 238) 

 Herr Archenhold describes the occultation of a twelfth- 

 magnitude star by the nucleus of the comet on December 5. 

 and, among other things, records that no appreciable 

 change of the colour of the star was caused by the super- 

 position of the comet ; the nucleus was sharply defined, 

 and by Argelander's method Herr Archenhold found that 

 its magnitude was ii-S. 



Other Periodic Comets .due .to Return this Year. — 

 In addition to Tempel's second, and D '.Arrest's comets, 

 five other periodic comets may be picked up during igio, 

 and notes concerning them are given in No. i, vol. xviii., 

 of Popular Astronomy (January, p. 47). 



Giacobini's comet, iSg6 v., passed perihelion in 

 December, , igog, according to the latest calculations, and 

 its detection now is unlikely. Swift's comet, iSgj ii., is 

 due at perihelion during the present month, but is un- 

 favourably placed. .Spitaler's comet, iSgo vii., is, accord- 

 ing to the recent calculations of Dr. Hopfer (Astronomische 

 Nachrichten, No. 4371), likely to pass perihelion early in 

 October, and might, had a search been made, have been 

 recovered in 1003 ; between i8g7 and 1903 this comet 

 suffered considerable pertin-bations by Jupiter, which 

 lengthened its period from 6.42 to 682 years. Faye's 

 comet is due at perihelion, in very favourable circum- 

 stances, in the latter part of October, and Brooks's comet, 

 iSSq v., is more likely to be seen during the summer of 

 loio than when near perihelion in January, igii. 



Winnecke's Comet. — In No. 4383 of the Astronomischr 

 Nachrichten Dr. Perrine states that Winnecke's comet will 

 soon be too faint for him to follow with the 12-inch re- 

 fractor at Cordoba. .As it is moving northwards rapidlv, 

 he suggests that further observations mav be secured with 

 the larger instruments of the northern hemisphere. Dr. 

 Tlillebrand's ephemeris for this object appeared in No. 4374 

 of the Astronomische Nachrichten, and Dr. Perrine states 

 that observations made on iqog December 10 gave a correc- 

 tion (Obs.-Eph.) of R..A., — sss. ; dec, o'. 



The Epoch of the Last Sun-spot Maximum. — In No. 

 12, vol. xxxviii., of the Memorie della Socicta dcgli 

 Spettroscopisti Jtaliani, Dr. Wolfer discusses the epoch of 

 the most recent sun-spot maximum. The observations 

 show that the spot activity was maintained from 1005 to 

 igo8, but, as there was a marked diminution in the latter 

 year, continued in iqoq, he concludes that the maximum 

 is passed, and proceeds to determine its epoch. This is 

 NO. 2100, VOL. 82] 



not a simple matter, because there were three marked 

 waves, reaching their maxima in November, igo5, July, 

 igo6, and February, igo7, respectively, and three smaller 

 ones ; in this respect the maximum strongly resembles that 

 of i82g and, less so, that of 1804. However, from the 

 relative numbers Dr. Wolfer obtains iqo6-i as the prin- 

 cipal maximum, and from the same data, compensated, 

 1906-4. This gives the interval from the preceding maxi- 

 mum as 12.3 years, 1-2 years in excess of the mean period 

 ii-i years. With regard to the intensity of the maximum. 

 Dr. Wolfer finds that 1906-4 follows those of 1884 and 

 1894, making the third maximum of feeble intensity, and 

 he discusses the observations made since 1750, showing 

 I hat periods of great and small maxima follow alternately. 



" -Annuario " for iqio OF tfh; Madrid Ohsf.rvatorv. — 

 The annual publication of the Madrid Observatory is a 

 substantial volume of 560 cap. octavo pages, and contains, 

 inter alia, the usual calendars and astronomical tables, a 

 dissertation on the nature, distances, motions, &c., of 

 stars, and a resumi^ of the solar observations made at the 

 observatory during igo8. The prominence observations are 

 tabulated in detail, and then summarised in the form 

 emplo.ved by Prof. Ricco. Meteorological results are also 

 given. 



.4 STUDY OF BARK-BEETLES. 

 'T'HE entomological publications of the United Slates 

 Department of Agriculture have for long past been 

 the admiration of European naturalists. Exceptionally 

 valuable, even among that Department's series of excel- 

 lent memoirs, are two recent papers on Scolytid beetles 



Fig. I. — Eastern Spruce Beetle {Dendroctonus picca/rerda). i, Dorsal 

 aspect ; 2, lateral aspect ; 2rt,» prothorax ; 2i, end of elytron, showing 

 sculpture; 9 . <5 1 seventh abdominal terga of female and male (the clear 

 oval spaces are stridulating areas; 3, pupa, dorsal aspect with spines 

 more highly magnified ; 3a, head and prothorax of pupa, lateral aspect ; 

 4, larva, lateral aspect ; 4«, terminal abdominal segments of larva, dorsal 

 view ; 4<^, abdominal segments of larva, ventral view. 



of the genus Dendroctonus by Dr. A. D. Hopkins, one 

 (Technical Series, No. 17, part i.) being in the main 

 systematic and descriptive, the other (Bulletin No. 83. 

 part i.) dealing for the most part with the bionomics of 

 the beetles and the rdle played by the various species as 

 depredators in North American forests. These papers con- 

 tain some of the results of seventeen years* original re- 

 search ; probably no such descriptions and figures of the 



