October 6, 1910] 



NATURE 



439 



tioned in these columns on September 8. This position 

 lies in Sagittarius aljout \\° south-west of tlie fifth- 

 magnitude star u, and is on the meridian about 7.30 p.m. 



As the magnitude of the comet is given as 13-0, it is 

 unlilcely that observations in these latitudes will be possible 

 for some time, but the southern declination is decreasing, 

 and perihelion passage is not due until January 8, igii. 

 According to the ephemeris, the cornet was at its nearest 

 point to the earth early in August, and its present distance 

 is about ISS million miles. 



The Luminosity of Comets. — As a reprint from Science, 

 N.S., vol. xxxii.. No. S17, we have received a paper in 

 which Mr. W. L. Dudley discusses the causes which pro- 

 duce luminosity in cometary bodies. According to the 

 author's reasoning, luminous comets are simply masses of 

 gaseous matter illuminated by the heavy electric discharges 

 constantly flowing from the sun to each of the planets. 

 The " ionic breeze " thus produced renders the comet 

 luminous, and at the same time brushes matter along with 

 it to form the tail. Should the comet get into such a 

 position as to be under the influence of two planets 

 (kathodes) at the same time, more than one tail is pro- 

 duced by the streams of ions from the sun (anode). The 

 author also offers explanations on this hypothesis for the 

 production of multiple heads, the change of direction which 

 sometimes takes place in the tail, and the polarisation of 

 cometary light. 



COLOL-RED St.WS between THE POLE AND 60° N. 



Declin.ation. — In continuation of previous lists, Herr 

 Kriiger now publishes, in No. 4441 of the AsUononnsche 

 Nachrichten, a list of coloured stars which lie between 

 the North Pole and 60° N. declination. The list includes 

 191 stars, and for each object gives the catalogue 

 numbers, the colour on the Potsdam scale, Herr Kriiger's 

 observed colour, on a scale where 0'-= white, 10- = red, 

 the magnitude and the spectral type. Ninety-three of the 

 stars lie within the colour-limits \VG-G — , and are of the 

 second and third types. 



Observations of tme Companion of Sirius. — The 

 observations of the companion of Sirius, made with the 

 40-inch refractor by Prof. Barnard during November 30, 

 1909, to March 15, are recorded in No. 617 of the Astro- 

 nomical Journal. The values for position-angle and 

 distance, for the mean epoch (igio.iob), are 89-09° and 

 <) 07" respectively. 



The Perseid Shower, 1910. — In a note appearing in 

 No. 617 of the Astroiioiuical Journal Mr. E. F. Sawyer 

 describes the meteor observations made by him at North 

 Weymouth, Mass., on August 9, 11, 12, and 13. The 

 hourly rates for one observer, covering one-sixth of the 

 visible sky with the centre in Perseus, were 15, 15, 8, and 

 6 on these respective dates. The meteors generally were 

 bright, and left streaks for one or two seconds ; the 

 radiant was found to be at 38-5°, H-55-5°. 



A Modified Method for Nadir Observations. — In 

 making the ordinary nadir observations, where a bright 

 thread is made to coincide with its reflected image, there 

 is always some little doubt as to when exact coincidence 

 occurs. To obviate this difficulty, Mr. R. M. Stewart 

 suggests a method where the reflected bright image is 

 obliterated by a dark thread. Experiments made with the 

 Ottawa meridian circle show that this method is simple, 

 and gives greater accuracy than the older one. In making 

 the observation, the bright reflected image and the 

 illuminated thread are brought nearly to coincidence as 

 usual, but the eye-piece, or attached plane mirror, is then 

 slightly rotated so that the field becomes dark and the 

 thread invisible, although the reflected image remains 

 bright. A slight motion then causes the dark thread to 

 occult the bright image, and it is stated that this opera- 

 tion can be performed with much greater certainty than 

 can the bringing into exact coincidence two bright lines 

 (Journal R.A.S. Canada, vol. iv., No. 4). 



.\ New Micrometer. — Dr. Doberck describes a new 

 micrometer in No. 4432 of the Astronomische Nachrichten 



. made to his specifications by Messrs. Cooke and Son. In 

 this instrument the frame carrying the wires is the only 

 readily movable part, so that there is practically no fear 

 of dragging, and the whole is built very rigidly and 

 strongly, thus obviating any likelihood of derangement. 



The errors of the screw, as shown by an investigation 

 involving 4000 settings, are extremely small, the correc- 

 tions being considerably below the probable errors of 

 setting on stars. The instrument is called the Elizabeth 

 Thompson micrometer. 



The Mean Parallax of Tenth-magnitude Stars. — From 

 a number of measures, made during 1907-g, of the Engel- 

 hardt companions of Bradley stars. Dr. H. E. Lau finds 

 that the mean parallax of tenth-magnitude stars, taking 

 Campbell's value for the sun's velocity, is o-ooio" ; this 

 is smaller than the value found by Comstock. The value 

 derived by Kapteyn's method should be o-ooii", so that 

 it would appear that these faint stars are not abnormal 

 in constitution, nor is there indicated any marked absorp- 

 tion in space (Astronomische Nachrichten, No. 4430). 



HALLEY METEORS. 

 r N a communication to Dr. \V. J. S. Lockyer, Prof. 

 David Todd, of the Amherst College Observatory, 

 writes as follows : — 



" .So well established is the Schiaparelli-Newton theory 

 of the connection between comets and meteors, that it is 

 highly important to obtain, observations from every 

 possible radiant, in order to ascertain whether there may 

 be any that do not conform to the general law. 



" Particularly is it desirable to observe the meteors of 

 the Halley stream. Prof. W. H. Pickering directed atten- 

 tion to the possibility of observing such meteors early 

 last May, when the earth was at its nearest, not to the 

 comet, but to the comet's orbit. Many astronomers kept 

 an outlook for these meteors; and on the night of 

 .M.ny 5-6 I made a balloon ascension for this purpose, with 

 a certainty of clear skies, as the spring season had been 

 especially cloudy. However, hardly more meteors than 

 usual on a May night were seen, and none of them 

 appeared traceable to the Halley radiant. Indeed, I had 

 very little expectation of seeing Halley meteors on that 

 occasion, as the region of the cometary orbit then nearest 

 to us was that through which the comet had passed 

 seventy-five years ago. 



" Quite different will be the conditions next month. On 

 October 18 the earth is closest to that region of Halley 's 

 orbit where the comet passed on March 13-15, 1910, and 

 from which, therefore, it may be expected that many 

 meteors will enter the earth's atmosphere, as the comet 

 has visited that region so recently. Very unfortunately, 

 the moon fulls at just that time, so that all the faintest 

 shooting stars would be lost. 



" Probably it will be well to begin the watch as early 

 as October 15, as evidently the meteoric matter in this 

 case is widely scattered along the comet's path." 



According to the Daily Mail of October 4, a very 

 brilliant meteor is recorded to have been observed at 

 Johannesburg on October 3. Perhaps this may be a 

 forerunner of the swarm referred to by Prof. Todd. The 

 account of this large meteor is as follows : — 



" Johannesburg, Monday. 



" Johannesburg was startled at 8.50 this evening by 

 the largest shooting star or meteor ever seen in the 

 district. 



" Its light was equal to that of a naval searchlight at 

 fifty yards' range. The sky was illumined for three 

 minutes, and the streets were as light as if it were day. 

 Natives were terrified, believing that the end of the world 

 was at hand. 



" The astronomical observers at the local observatory 

 were nearly blinded. The director of the observatory 

 estimated that the meteor was only 150 miles from the 

 earth. The head of the meteor, he says, was pear- 

 shaped and half the size of the moon in diameter. The 

 tail was straight at first, but afterwards turned towards 

 the south." 



NO. 2136, VOL. 84] 



