JuLV 1 6, 1908J 



NATURE' 



^05 



that the work is of the highest order, and affords ample 

 evidence of the close association of the institution with the 

 manufacturers of Germany. The idea of publishing in 

 the technical Press an account of woric done is a good 

 one, and might well be followed by similar institutions 

 with which manufacturers have not yet learnt to cooperate 

 as much as they might. 



The Physikalische Zeitschrift for July i contains an 

 account of some observations made by Dr. S. Landau, of 

 Gottingen, on the magnetic rotation of the plane of 

 polarisation in rock salt, Iceland spar, water, and alcohol, 

 w'ith the view of testing the theories which have been 

 advanced in explanation of the phenomenon. His method 

 is a photographic one, the light from an iron arc passing 

 through a polarising prism, the magnetic field, a half- 

 shadow prism, and a spectrograph in succession, the slit 

 of the latter instrument being at right angles to the 

 dividing line of the half-shadow field. Several photographs 

 are taken on the same plate, the polarising prism being 

 rotated through a small angle between each, and from 

 inspection of tnese the position of the prism for equal 

 intensity of the two halves of a line in any part of the 

 spectrum is found. The author concludes that the electron 

 theory is capable of reproducing all his observations, but 

 that some of the constants which, if only negative electrons 

 are assumed to play a part in the phenomenon, should 

 come out positive, have negative values, and suggest, 

 therefore, that the positive electrons play a part. Against 

 this, however, many objections may be raised. 



In the note upon the seventh International Congress of 

 Applied Chemistry in last week's Nature (p. 229), it 

 should have been stated that Sir William Ramsay, K.C.B., 

 F.R.S., will be the acting president of the congress, and 

 Sir Henry Roscoe the honorary president. We are in- 

 formed that Prof. Nasini will not give one of the lectures 

 to the congress, but a lecture will be given by Prof. Paterno, 

 of Rome. 



In the issue of Nature for June 2, 1904 (vol. Ixx., p. 107), 

 an optical illusion observed by Dr. T. Terada, of the 

 College of Science, Tokyo, was described. Dr. Terada 

 directs attention to another illusion he has remarked. After 

 watching drops falling at the rate of about one a second 

 into the centre of a small pool, and so causing circular 

 ripples, he turned his eyes to a spot on a neighbouring 

 bush. The bush appeared to contract slowly towards the 

 point looked at, but the contracting motion was slower 

 than the diverging motion of the. ripples. A similar effect 

 was noticed by loolcing at the ground or at a wall. 



OUR ASTRONOMICAL COLUMN. 



Saturn's Rings. — The June number of the Astrophysical 

 Journal (vol. xxvii., No. 5, p. 363) contains a note by 

 Prof. Wright in which he discusses the bright beads, or 

 knots, which were observed during the recent opposition 

 when the unilluminated surfaces of the rings were turned 

 earthwards. Criticising Prof. Barnard's recent explanation, 

 in which the author supposed the brightness of the beads 

 to b'e due to light percolating by many reflections through 

 the masses of meteorites composing the rings, he points out 

 that whilst this is probably true for the cr.ipe nng, it 

 seems impossible that sufficient light to produce the outer 

 bright knots could pass between the more densely packed 

 meteorites of the outer rings. Then turning to Bond's 

 explanation of the phenomena, Prof. Wright shows that 

 it accounts for the bright outer knots and for the very 

 slight, asymmetry which is suggested by comparing the 

 measures of different observers. He further suggests that 

 it is not unlikely that collisions among the meteorites may 

 account for some, at least, of the observed luminosity over 

 the surfaces of the two dense rings and in the knots. 



NO. 2020, VOL. 78] 



New Photographic Celestial Charts. — On a supple- 

 mentary sheet to No. 4257 of the Astroiioiiiische 

 Nachrichten, Prof. Johann Palisa invites subscriptions to 

 a series of photographic star charts prepared by Prof. 

 Max Wolf at Heidelberg. Having received copies of his 

 maps privately from Prof. Wolf, Prof. Palisa found that 

 his work of finding minor planets was reduced by 75 per 

 cent., so he suggested that the sheets should be published, 

 as they will undoubtedly prove very useful in other 

 branches of astronomy. The sheets will be printed on 

 smooth matte bromide paper with a degree reseau, and 

 each sheet will include some fifty square degrees, the scale 

 being such that i° = 36 mm. This enterprise is purely a 

 private one, of which the cost must be borne by the sub- 

 scribers, so that Prof. Palisa invites all who wish to sub- 

 scribe to apply to him as soon as possible, and before 

 December 31 at the latest; the price of the series con- 

 taining twenty sheets is thirty shillings, and after the 

 date name'd must be forty shillings. The maps reproduce 

 stars down to about the fourteenth magnitude. 



Double Stars. — An example of the good work that may 

 be done by an amateur astronomer with but a moderate- 

 sized instrument appears in No. 4259 of the Astronotnische 

 Nachrichten, where a list of double stars discovered and 

 observed by Mr. E. D. Roe, jun., of Syracuse, N.Y. 

 (U.S..\.), with a 6J-inch Clark refractor, is published. 

 His observatory was erected in July, 1906, and by the 

 end of 1907 he had independently discovered some 250 

 double stars (generally separated by less than 10"), of 

 which he has since identified a number with doubles 

 given by Prof. Burnham. The present list contains the 

 measures of the stars thus identified. 



In the same journal Herr J. Fr. Schroeter publishes a. 

 list of corrections to Prof. Burnham's " General Cata- 

 logue " for double stars included in the Christiania zone. 



No. 4260 of the Astronomische Nachrichten (p. 185, 

 July 3) contains a discussion by Herr E. Schoenberg. of 

 Dorpat, of the orbits of several double stars, including 

 e 5S1, ;8 SS3, S Sextantis = AC.5, and ^ 612. 



The Albedoes of Jupiter's First and Third Satellites. 

 — In the July number of the Bulletin de la Sociiie 

 astrouoniique de France, M. Out^'nisset records some 

 observations made in January and March showing the 

 relatively low albedoes of the surfaces of Jupiter's first and 

 third satellites. The disc of Ganymede when seen outside 

 the planet was quite brilliant, but when projected on to 

 the surface of the planet, during a transit, it became less 

 and less bright until when near the central meridian it 

 was very dark, in fact nearlv as dark as its own shadow. 

 This was observed on January 22 and March 12, and the 

 same phenomenon, somewhat less marked, was observed' 

 in the case of the first satellite on March 27. As the 

 satellites were projected on the bright equatorial band of 

 the planet, it follows that the albedo of this region must 

 be greatly superior to the albedoes of the two satellites. 



A Bright Meteor. — No. 4258 of the Astronomische 

 Nachrichten contains a record of a bright meteor observed 

 by Dr. J. Kavdn at the Prag-Smichow Astronomical Insti- 

 tute on November 16. 1907, During its flight the meteor 

 was seen to explode into two parts, but no trail, or 

 detonation, was observed. The brightness of the object 

 was about equal to that of Venus, and its flight, as 

 observed by Dr. Kavdn, was from a=i96''.2, 5 = -i-57°-7i to 

 a=i62°.9, S = 4-46°.7; simultaneous observations by Herr 

 L. Stetka gave approximately the same positions for the 

 appearance and disappearance. 



Latitude Variation. — When the international latitude 

 service was instituted in 1899 the Cincinnati Observatory 

 was asked to cooperate, and has made continuous ob- 

 servations since. As changes in the star-list w'ere made in 

 1906 it seemed to Dr. Porter to afford a good opportunity 

 to discuss the observations made. to that date; this he does 

 in No. i5 of the Publications of the Cincinnati Observatory, 

 giving .an historical account of the observations, a descrip- 

 tion of the instruments and methods used, and a table of 

 the observed latitudes day by day. From the yearly values 

 given it is seen that the different years show considerable 

 fluctuations, signifying that the annual digressions are not 

 symmetrical with reference to the determined mean position. 



