i8o 



NATURE 



[December 8, 19 lo 



Ijodies in the visible spectrum. Two experimental methods 

 were used : — (i) The author's " elliptic analyser," described 

 by Dr. Zakrzewski in 1907, and used since with success 

 •by Herr Volke ; as shown in the paper, this arrangement 

 provides a comparatively exact way for the determina- 

 tion of the refractive index v and of the index of extinc- 

 tion K for a metallic body. (2) A new scheme depending 

 -on the use, for the observation of ellipticity, of a con- 

 vergent pencil of light ; the results thus obtained are 

 estimated to be correct within 5 per cent, of their values. 

 Illustrative results for platinum, cobalt, and graphite are 

 adduced. Maxwell's simple equation »/- - /c' = const., now 

 given up on theoretical grounds, is found to hold true for 

 ^graphite. The second correlative equation, however, 

 asserting the proportionality of the product vk with the 

 period of vibration in the incident beam of light, does not 

 agree with, the observations. 



An interesting address on " Comets and Electrons " was 

 •delivered by Prof. Augusto Righi to the Bologna Academy 

 on June 22, and is published as No. 13 of Altualitd 

 scientifiche (Bologna : Nicola Zanichelli, 1910, price 2.50 

 lire). In the paper Prof. Righi traces the growth and 

 ■development of ideas regarding radiation-pressure, the 

 successive proofs, disproofs, and reproofs of its existence 

 for finite bodies, for minute solid particles such as are 

 believed to exist in comets' tails, and for gaseous mole- 

 cules, the theory of formation of the tails themselves, the 

 electrical phenomena accompanying them, the escape of 

 gases from planetary atmospheres, the nature of sun-spots 

 and allied astrophysical phenomena. Prof. Righi, in con- 

 clusion, refers to the experiments conducted during the 

 passage of the earth through Halley's comet, a large pro- 

 portion of which gave rise to no definite conclusions. The 

 following suggestive remark occurs in the paper : — 

 "" In this connection of the action of radiations on the 

 individual molecules of a gas, and hence on the presence 

 of gases in comets' tails, there has been once more verified 

 the not uncommon fact that conclusions which are just, 

 or regarded as such, are reached only by an asymptotic 

 method, that is, after a series of successive corrections, 

 and often, as in the present case, after having completed 

 a series of successive oscillations, fortunately of decreasing 

 amplitude, from one side to the other of the truth." 



A COMMITTEE was appointed about two years ago by the 

 Institution of Civil Engineers to investigate and report on 

 questions connected with the use of reinforced concrete. A 

 preliminary and interim report has now been issued giving 

 information regarding the conditions under which rein- 

 forced concrete has been employed in engineering work in 

 various countries, and the views of engineers having special 

 experience in its use. The committee does not accept any 

 responsibility for any of the statements contained in the 

 report, and reserves its own views and recommendations 

 until later. Hence the designer will still have to depend 

 largely on the excellent report presented some time ago 

 by the Royal Institution of British Architects, more 

 especially as he will find difficulty in extracting definite 

 information from the present report. The reader is ex- 

 pected to compare for himself the various statements of 

 opinions contained in 262 pages of letterpress. The com- 

 mittee is now engaged upon tests and investigations in 

 order to enlarge the knowledge at present available, and 

 no doubt more definite information and conclusions will 

 appear in a subsequent report. 



Messrs. Newton and Co. have been granted a warrant 

 of appointment as opticians to the King. They have held 

 Royal warrants for more than sixty years. 

 NO. 2145, "^OL. 85] 



OUR ASTRONOMICAL COLUMN. 

 EpheAeris for Faye's Comet, iQioe. — Dr. Ebell pub- 

 lishes a continuation of the ephemeris for Faye's comet in 

 No. 4457 of the Astronomische Nachrichten ; the following 

 is an extract : — 



Ephemeris i2h. (Berlin M.T.). 



6 (true) 



log r 



log A 



1910 o (true) 



h. m. 



Dec. 6 ... 3 37*1 ... +3 44-0 ... 02270 ... 9'87i7 ... 10-3 

 „ 10 ... 3 37-6 ... +3 25-0 ... 0-2292 .. 9 8«45 ••• '0-3 

 ,, 14 ... 3 38-5 ... +3 12-8 ... 0-2316 ... 9-8985 ... 10-4 

 ,, 18 ... 3 39'S ••• +3 7*1 ••• 02342 ... 9-9134 ... 105 

 „ 22 ... 3 41-6 ... +3 7-5 .. 0-2371 ... 99290 ... 10-6 

 ,, 26 ... 3 43-7 ... +3 13-3 ... o 2401 ... y-9453 .-. io7 

 „ 30 ... 3 46-3 ... +3 24-t ... 0-2433 • •■ 9'962i ... IO-8 

 This ephemeris is calculated from Prof. Stromgren's 

 elements with a correction AM., and the time of peri- 

 helion is brought forward by about +S-gi days, to 

 November 1-647 (Berlin M.T.) ; an observation at Teramo 

 on November 23-4 gave a correction of —9s., —2-1', to the 

 ephemeris position. 



Recent Helwan Photographs of Halley's Comet.- — 

 Halley's comet was again photographed with the 

 Reynold's reflector at the Helwan Observatory on 

 November 7, 9, and 11, and the plates indicate a correc- 

 tion of +o-2m., o', to the ephemeris published in No. 4450 

 of the Astronomische Nachrichten ; the magnitude is esti- 

 mated at about 14-5. 



A telegram from Prof. Frost announces that Prof. 

 Barnard observed the comet (presumably with the 40-inch 

 refractor) at the Yerkes Observatory on November 11 at 

 i7h. i7-8m. (M.T. Yerkes), and found its magnitude to 

 be about ii-o; the observed position was 



R.A. = i2h. 4m. 2I-3S., dec. = — 14° 54' 15*. 



From these observations it would appear that there is 

 a marked difference between the photographic and visual 

 magnitudes, and, curiously enough, it seems that the visual 

 brightness is the greater (Astronomische Nachrichten, 

 >>'o- 4457)- 



The Total Eclipse of the Moon on November 16. — 

 Some interesting notes dealing with observations made 

 during the recent eclipse of the moon appear in No. 21 of 

 the Comptes rendus (November 21). MM. Luizet, 

 Guillaume and Merlin, at the Lyons Observatory, observed 

 the occultations of several stars, and found that in some 

 cases the disappearances were not instantaneous. In two 

 cases the star appeared to be projected on the disc before 

 disappearing, and in one case contact with the limb pre- 

 ceded disappearance by three seconds. On the other hand 

 several well-observed occultations and reappearances were 

 quite sudden. 



M. Montangerand, Toulouse Observatory, noted that 1p 

 one case the extinction took an appreciable time, but ii: 

 two others it was instantaneous ; he also directs attentior 

 to the apparent unevenness of the shaded disc. M. Lebeuf, 

 at Besan^on, also noted this phenomenon, and describes 

 the apparent rotation of the deeper coloration as the eclipse 

 proceeded. The general transparency of the shadow, as 

 compared with earlier eclipses, notably that of April 11, 

 1903, also attracted his attention. 



M. Jonckheere, at the Hem Observatory, was able to 

 see the penumbral shadow, with the naked eye, at 

 loh. 32m., and observed first contact with the shadow at 

 loh. 57m. 5s. (M.T. Hem). He also records that the 

 meteorological observations, presumably delicate, indicated 

 a sensible lowering of temperature during totality. 



The Probable Errors of Radial-velocity Determine 

 TIONS. — The radial velocities of stars are now bein;_ 

 measured by many observers, not always with concordar 

 results, and it becomes important that the probable error- 

 of such observations should be investigated and define' 

 with every care. In a paper in No. 3, vol. xxxii., of th- 

 Astrophysical Journal (p. 230), Mr. Plaskett deals with 

 this subject, basing his discussion on exhaustive experi- 

 ments he has made at the Ottawa Observatory. Man} 

 factors enter the problem, and one of the most importair 

 is the effect of dispersion. Mr. Plaskett finds that, con- 

 trary to expectation, the accuracy is not inversely propor- 

 tional to the dispersion of the spectrograph used, only a 



