592 



NATURE 



[May 6, 1922 



features on Jupiter have been obtained recently by- 

 Mr, Frank Sargent at the University Observatory, 

 Durham. The Red Spot Hollow was observed in 

 transit across the central meridian on various dates 

 and its longitude determined as follows : 1921, Dec. 

 12 =26o°-9, Dec. 22 =259°-7, 1922, Feb. 21 =257°-4, 

 March 10 =256°-o, March 31 =256°-i, April 10 =254°'2. 

 These positions show a slowly decreasing longitude 

 equivalent to a rotation period of 9h. 55m. 38-43. 

 This is a decidedly lower rate than the spot exhibited 

 about four years ago when the period was 9 h. 55 m. 34 s. 

 The south tropical disturbance, which is now about 

 140° long, was central on April 6 in longitude 46° so 

 that it follows the Red Spot Hollow by about 152°. 

 Its rate of rotation during the present year has been 

 about 9 h. 55 m. 32 s. or 6 seconds less than that of the 

 Red Spot Hollow. In 1901 the difference of rota- 

 tional velocity in the two objects amounted to 22s. 

 but since that time the motions have been gradually 

 approaching uniformity and may possibly in a few 

 years become identical. Mr. Sargent has recently dis- 

 covered a somewhat abnormal dark marking on the 

 northern edge of the southern equatorial belt, and 

 finds its rotation period to be gh. 51 m. 6 s. from 27 

 rotations performed from March 31 to April 11. He 

 is continuing to follow this and other interesting 

 features with his loj-inch reflecting telescope. 



Observations of Venus. — Pop. Ast. of March 

 contains a study of this planet by Mr. Alfred Rordame. 

 He has observed it regularly for 20 years with aper- 

 tures between 4 and 16 inches. In 1921 he took 

 several photographs during daylight with a 9-inch 

 Alvan Clark refractor. Some of these are reproduced, 

 and show some indubitable spots, which are confirmed 

 on more than one negative. Naturally the chief 

 interest concerns the rotation period. He notes that 

 at first he accepted Schiaparelli's value, but now he 

 has come to think that a value near 24 hours is correct. 

 As illustrating the difficulty of the observations, he 

 notes that on less than fifty occasions has he seen 

 definite markings, and on six only has a positive 

 movement of the spots been observed. Some drawings 

 showing this are reproduced. One pair, taken on 

 October 8-9, 1916, tend to confirm De Vico's period 

 of 23 h. 21 m. ; Mr. Rordame thinks that those spectro- 

 scopic determinations which were made in daylight 

 are liable to error, owing to the blending of the sky 

 spectrum with that of the planet. He considers that 

 the planet is normally covered with dense clouds, 

 the height of which is probably very great. 



The same number of Pop. Ast. contains a note by 

 Prof. St. John on a photograph of the red end of the 

 spectrum of Venus ; the dispersion was so great that 

 the telluric lines would have been separated from 

 those due to Venus's atmosphere by the Doppler 

 effect. No companions, however, were visible to the 

 telluric oxygen bands ; it is concluded that oxygen 

 is practically absent from the upper atmosphere of 

 Venus. 



Solar Researches. — The February number (vol. 

 34, No. 197) of the Publications of the Astronomical 

 Society of the Pacific contains several communications 

 on solar work. The first is a general article on the 

 sun by 'Ferdinand Ellerman. "The Zeeman Effect 

 on the Sun " is the title of the next article by Adrian 

 van Maanen, written and translated from the Dutch 

 journal Physica, the October (1921) number of which 

 was dedicated to Dr. Zeeman in recognition of his 

 discovery, 25 years ago, of the separation of spectral 

 lines in a magnetic field. This article is of great 



interest, summing up the fine work done at Mount 

 Wilson after Hale's important discovery of magnetic 

 fields in sun-spots. Hale himself contributes a note 

 on " Invisible Sun-spots," this term designating the 

 invisible stage of spots which are usually visible 

 during the greater part of their existence. By means 

 of the apparatus which he describes, Hale indicates 

 the importance of making a systematic search for 

 local magnetic fields which may betray the presence 

 of incipient or dying spots. Seth B. Nicholson gives 

 a summary of Mount Wilson magnetic observations 

 of sun-spots for November and December last, and 

 describes the scheme of classification underlying the, 

 tables he produces. Systematic observations of the 

 magnetic polarities of sun-spots have been made daily 

 with the 150-foot tower telescope since 1915, and 

 preparations are being made to publish all this valu- 

 able new work in detail. Spot groups are divided 

 into three classes and designated unipolar, bipolar, 

 and complex, and some interesting facts ab'^ut their 

 appearances are given. 



Proposed 50-FOOT Reflector. — A somewnat wild 

 scheme is said to be contemplated by Prof. Todd and 

 Mr. McAfee. This is the construction of a 50-foot 

 reflector of 1200 feet focus, by utilising a mine-shaft 

 of this depth at Chauaral, Chile, in the Andes, in the 

 locality where Mars will pass exactly overhead at the 

 opposition of 1924. The reflector will consist of 

 rotating mercur}'-, and there must be considerable 

 incredulity about the possibility of keeping this 

 sufficiently free from tremors and eddies to give 

 tolerable definition. The plan ascribed to Prof. Todd 

 is to use a flat, which throws the image into a cave at 

 the side of the shaft, where the camera would be put. 

 But clearly, with such high magnification, the shortest 

 practicable exposure would give a blurred image on 

 a stationary plate. A much better plan would seem 

 to be to put a girder across the mouth of the shaft, 

 carrying a plate-holder or eyepiece which could be 

 moved by clockwork at the appropriate speed (about 

 I inch per second). This is known as the Schaeberle 

 method in eclipse photography, and has given satis- 

 factory results. Prof. Todd is well known for bold 

 and striking experiments, and all will wish him well, 

 though without much'expectation of success. 



A' Catalogue of Double Stars. — A Greenwich 

 volume has lately been published containing the 

 measures of double stars made with the 28-inch 

 refractor between 1893 and 1919. Earlier observa- 

 tions are given for many stars, and in an exhaustive 

 series of notes, mainly by Mr. Jackson, the character 

 of the motion is discussed and the deviations from 

 published orbits indicated. There are also 25 new 

 orbits, computed by him, many of which deviate con- 

 siderably from earlier determinations. Hypothetical 

 parallaxes are deduced for all stars for which orbit 

 elements are available, and also for other stars which 

 have been observed over an arc sufficiently long to 

 indicate the amount of curvature. The assumed 

 mass of each pair is twice the solar mass ; this 

 assumption gives a solar velocity of 19 km. /sec, 

 which is in close accord with the spectroscopic value. 

 Comparison of the hypothetical parallaxes with the 

 spectroscopic ones shows perfect accord, in the main, 

 in the case of orbit-stars, but in the arc-stars the 

 hypothetical parallaxes exceed the spectroscopic by 

 30 per cent. ; this is not an excessive error for such 

 small parallaxes (0-07" to 0-02"). There is some 

 indication of mass varying with spectral type, but 

 this has not been used in obtaining the results. 



NO. 2740, VOL. 109] 



