Dec. 4, 1879] 



NATURE 



117 



OUR ASTRONOMICAL COLUAfA 

 f A Seventh Star of the Orion-Trapezium. — In addition 

 to the well-known fifth and sixth stars in the trapezium of Orion, 

 the former detected by Mruve with the Dorpat refractor on 

 November II, lS26, and the latter by Sir John Herschel with 

 Sir James South's large refractor at Kensington, on February 13, 

 1830, the elder Bond, sion afttr the mounting of the Harvard 

 instrument, perceived, roughly in the direction of the sixth star, 

 a fainter and more distant one, which is No. 24 of his memoir on 

 the nebula published in 1848. M. O. Struve, with the telescope 

 of similar dimensions at Pulkowa, could not see this star, a 

 circumstance which might be attributable either to variability, or 

 to the difference of altitude of the object at Pulkowa and at 

 Harvard College. It was repeatedly observed by G. P. Bond, 

 and is No. 636 of his catalogue printed in Annals of the Astro- 

 nomical Observatory of Harvard College, vol. v., where its 

 magnitude is estimated to be 13*3 on Argelander's scale. The 

 Pulkowa measures gave for the sixth star position I2S°"8, 

 distance 3"'73 at the epoch 1S5S7S ; from the Harvard 

 differences of right ascension and declination we find, for 

 the seventh star, position 136 , distance I2"'i. In Bond's later 

 notes the following references to this star, amongst others, 

 occur : — 1S63, January 19 and 23, difficult ; January 30, easy, 

 though faint ; February 14, not difficult, though requiring atten- 

 tion and effort. 1864, February 3, under fine definition, though 

 easily seen, probably fainter than in the previous year; February 

 29, readily seen and possibly brighter. Referring to the notes 

 in 1S50 and 1S51, it is remarked that the star is "often men- 

 tioned in these earlier observations ; as certainly seen on the 

 dates 1850, February 7, March 2, March 5, March 11 ; it is not 

 mentioned March 10, and was not seen March 12; not men- 

 tioned 1850, December 27, but seen again 1851, February 3." 

 It was observed on several occasions in 1S59 and i860. On 

 January 2S, 1S61, seen by glimpses, and on February 13 easily. 

 On January 31, 1S62, not seen. Some of these observations 

 might appear to point to variability, but others seem to afford 

 "another and quite different explanation ot the phenomena." 

 If we are not mistaken, this seventh star has been recently 

 caught up with the Ealing reflector ; but there are other tele- 

 scopes in this country wliich should be competent to cope with 

 it, and the star may deserve some attention. 



Lunar Eclipses. — In the small eclipse of the moon (magni- 

 tude C17) which will occur on the 2Sth of the present month, 

 the first contact with the shadow takes place at Greenwich at 

 3h. 37m. p.m., and the last contact at 5h. 1511. ; the moon rises 

 at 3h. 46m. Of the eight lunar eclipses occurring within the 

 following five years, only one, that of October 4, 1884, will be 

 wholly visible in this country. The circumstances of these 

 eclipses may be thus very briefly indicated : — 



1SS0, June 22. — Invisible, the middle at ih. 50m. p.m. 



Dec. 16. — Total ; beginning of total phase at 2b. 54m. 

 P.M., the moon rising at 3I1.' 46m. 

 iSSl, June 12.— In\i,iiile, the middle at 6h. 54m. A.M. 



Dec. 5.— Nearly total (0-97); first contact with the 

 shadow at 3I1. 28m. r.M., the moon rising 

 at 3I1. 50m. 

 1883, April 22.— Invisible, the middle at I ih. 39m. a.m. 



Oct. 16. — First contact with shadow at 5I1. 59m. a.m., 

 the moon setting at 6h. 25m. 

 1SS4, April 10. — Invisible, the middle near noon. 



Oct. 4. — Total, visible throughout, the middle soon 

 after 10 p.m. 



PARALLAX of a Small Star.— Dr. Gcelmuyden, of the 

 Observatory at Christiania, by a series of observations extending 

 over m n-e than twelve month-, finds "a notable parallax " for 

 the ninth magnitude star, No. 1 1677 in Oeltzen's Catalogue 

 from Argelander's northern zones. This star has a proper 

 motion of 3" x>4 in the direction 274 . The parallax appeals to 

 amount to about o"'25, but the result is considered far from 

 definitive. The position of this star is in U.A. nh. 13m. 49s 

 N.r.D. 23° 30' 2 for 1SS0. 



New Nekil.e in ERIDANUS, — M. Block has detected at 

 Odessa two nebula: in thi- constellation, which are not found 

 in Sir John Herschel's General Catalogue, the first in K.A. 

 3b. 2Sm. 9s., N.r.D. 116° i6'"S, the second in R.A. 3b. 33m. 48s. 

 N.P.D. n6°43' - 7 for 1880. The former is pretty bright, and 

 five minutes in diameter, the latter "considerably bright," with 

 strong central condensation, and readily observed even with the 



moon above the horizon. The repeated discovery of un- 

 catalogued nebula; in these days becomes of much interest in 

 connection with the question of variability. 



PHYSICAL NOTES 



Prof. Steinhauser, of Vienna, has recently pointed out 

 that there exists a determinate relation between the size and 

 relative position of the two views ol a stereoscopic picture, the 

 lenses of the camera with which it is taken, and the optical 

 arrangements of the stereoscope in which it is to be viewed. If 

 these relations are observed rightly, the effect of relief will be 

 much more perfectly attained for all parts of the picture than if 

 they are neglected. The eye-pieces of the stereoscope above the 

 plane of the photographic pictures ought to be made as nearly as 

 may be equal to the focal length of the objective of the photo- 

 grapher's camera, and this again should be about equal to the 

 mean distance of easy vision, or, from ten to twelve inches. 

 Herr Steinhauser, after developing the theory of the instrument 

 in relation to this point, throws out three very definite and simple 

 suggestions for the photographers. Firstly, that all stereoscopic 

 pictures should be taken with lenses of equal focal length, say 

 15 centimetres; secondly, that all should be made of equal 

 breadth, or about 75 millimetres ; thirdly, that the distances 

 between the centres of the objective lenses should always be kept 

 constant. 



The passivity of iron when employed as the positive pole of 

 a nitric acid battery, or as positive electrode of a voltameter cell 

 containing nitric acid, has recently been studied by M. Louis 

 Varenne, who concludes that the passive state is due to a film of 

 nitric peroxide which collects upon the surface of the iron and 

 protects it from further chemical action. M. Varenne states 

 that this film is apparent when the surface of the iron is ex- 

 amined under the microscope. He finds that the passive state 

 ceases if a stream of carbonic dioxide or of hydrogen is passed 

 through the liquid, and that solution proceeds apace. He also 

 find, tin t nitric peroxide gas is evolved from the passive iron 

 when it is placed in vacuo. 



Another new instrument may shortly he expected from the 

 atelier of Dr. Kbnig, which will probably settle for ever the 

 dispute between himself and Mr. A. J. Ellis as to the correctness 

 of his tuning-forks of normal pitch. It will indicate a variation 

 of one vibration in ten thousand from the assigned pitch. 



M. Pellat finds that Latimer Clark's standard cell is not 

 entirely free from variations in its electromotive force. He has 

 found t o similar cells may differ from one another by a quantity 

 equal to the T ^„th part of the electromotive force of a Daniell's 

 cell. M. Pellat employs an electrometer to measure the residual 

 difference of potential when the two cells are connected up in 

 opposition to one another, and believes that by this means his 

 observations are free from possible errors due to polarisation 

 when the galvanometer method of comparison is adopted. 



Herr. Edlund has drawn attention to an electrical experi- 

 ment that has not hitherto been thoroughly explained. Let an 

 open metal tube or cylinder, capable of rotation about its axis, 

 be placed <ver a magnet of double its own length, so that its 

 lower end is opposite the middle of the magnet, while its upper 

 end is opposite the magnet pole. Then let a current of elec- 

 tricity of sufficient strength be passed from one end of the tube 

 to the other. The tube is found to rotate with a velocity which 

 is independent of the resistance of the metal of which it is com- 

 posed and of its thickness. Longitudinal slits cut in the tube do 

 not affect its rotation. There is therefore here a complete con- 

 version of electromotive force into ponderomotive force. W. 

 Weber inferred that the resistance of the movable conductor to 

 the passage of the current is the medium of this transfer of the 

 energy, and argued that the first tendency is to rotate the current 

 in the conductor, but that as this could not be done without 

 moving electricity through the substance of the conductor, and 

 therefore against its resistance, the principle of lea»t heat requires 

 that the energy should be translerred in an indefinitely short 

 time to the conductor itself, which therefore rotates. Herr 

 Edlund, however, sees in the experiment a confirmation of his 

 ' ' unitary " theory of electricity. 



SlGNOR Guidi, an Italian engineer, has suggested the em- 

 ployment of electricity in the preparation of steel in the follow- 

 ing manner :— A dynamo-electric machine driven by steam or 

 water power is caused to electrolyse water ; the oxygen and 



