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NA TURE 



[September 23, 1922 



The reference in Nature of September 2, p. 324, 

 to the excellent series of wireless telephone receiving 

 sets which are being placed on the market bv the 

 Metropolitan Vickers Co., Ltd., contains a state- 

 ment which, if uncorrected, might lead to misappre- 

 hension regarding the completeness of the apparatus 

 sent out by the company. In referring to the 

 simplest of the sets, the remark was made that it 

 was not clear whether the battery was contained in 

 the case. The set in question, however, is fitted 

 with a crystal detector, and therefore no battery is 

 required ; and, indeed, this is one of its chief advan- 

 tages. In the case of the more expensive valve sets, 

 all the necessary batteries are included with the 

 apparatus, for the company makes a special point 

 of the fact that every outfit is sent out complete 

 in every respect. 



We have received from Leslie McMichael, Ltd. 

 (Providence Place, Kilburn), a catalogue of wireless 

 telegraph and telephone apparatus covering a con- 

 siderable range, and including not only complete 

 receiving sets of various types, but also extensive lists 

 of component parts and accessories from which 

 amateurs and others can make up equipment to cover 

 anv requirements on a moderate scale. We notice in 

 particular a very low-priced two-valve receiving set 

 for short wave-lengths which should fulfil the require- 

 ments of broadcasting but can easily be converted 

 to longer wave reception and greater sensibility when 

 desired. Some of the apparatus' listed has been 

 purchased from the Disposals Board and is offered 

 at favourable prices, and a few items are marked 

 German captured material, transformed as new. A 

 quantity of accessories for transmitting as well as 

 receiving apparatus is included. 



Our Astronomical Column. 



Mars. — An interesting example of the somewhat 

 unusual atmospheric conditions exhibited on Mars 

 at this apparition is described bv E. C. Slipher (Pub. 

 Ast. Soc. Pacific, Aug. 1922). This was a large white 

 equatorial spot situated at the south end of Mar- 

 garitifer Sinus ; it was about 800 miles long, 400 

 mdes wide, and comparable with the polar caps in 

 brilliancy, though slightly more yellowish. There 

 was no trace of it on July 8 ; it was very brilliant on 

 July 9; on July 10 it was larger but fainter, and 

 crossed by two greyish streaks; on July 11 it had 

 split into three separate portions, of which only one, 

 to the right of Margaritifer Sinus, remained on July 

 12. On July 13 and 14 the region had resumed its 

 normal appearance. Whitish patches are frequently 

 seen near the limbs, but they generally disappear 

 near the central meridian, indicating that they are 

 morning or evening mists or hoar frosts. This great 

 spot, on the other hand, persisted in full strength 

 throughout the Martian day. The article is illus- 

 trated by drawings and photographs, the latter being 

 on a small scale, but fully confirming the changes in the 

 aspect of the spot, which was probably cloud or mist. 

 Its appearance shows that conditions on the planet's 

 surface are by no means so-stagnant as some assert. 



Prof. W. H. Pickering contributes an article on the 

 planet to Popular Astronomy (Aug.-Sept. 1922). It 

 is in reply to one by Prof. Porter, and lays stress on 

 the broad dark band that is visible round the melting 

 polar cap ; he gives good reasons for thinking that 

 this is water, not carbon dioxide, and concludes that 

 the day-temperature, even near the poles, is above 

 freezing point, while at the equator it may rise to 

 1 He notes the green colour of the 



\ 1. 1 11,1 " after the melting of the polar caps, which he, 

 in common with many astronomers, ascribes to some 

 form of vegetation, another indication of a tempera- 

 ture above freezing point. From the frequent 

 presence of cloud or mist near the terminator, he 

 conjectures that the nights are generally cloudy, 

 which would tend to mitigate the severity of the 

 night frosts. He notes that Prof. Campbell's spectro- 

 scopic observation (quoted by Prof. Porter) did not 

 pn ivc the complete absence of water-vapour, but only 

 that its amount was less than a quarter of thai in the 

 earth's atmosphere. 



The Law of Solar Rotation. — The determination 

 of the law of rotation of the sun is an old problem, 



NO. 2760, VOL. I IO] 



first formulated by Carrington, who studied the 

 motions of spots as they moved across the solar disc. 

 As sunspots are confined to middle and low latitudes, 

 the law, based on actual data, was restricted to these 

 latitudes. The spectroscopic method of determina- 

 tion was a great step in advance, because a law could 

 be deduced which could be extended to the solar 

 poles. Spectroscopists have, until recently, been some- 

 what in difficulty with their results, for determina- 

 tions at different times by different observers have 

 resulted in formulae which did not agree. The fact is 

 that a law formulated from observations made at, 

 say, sunspot minimum is not applicable at a sun- 

 spot maximum, because the movements of the 

 vapours in the solar atmosphere vary from year to 

 year. This question of the variability of the sun's 

 rotation during a cycle of solar activity was raised 

 last year by Prof. Newall (Mon. Not. R.A.S., vol. 82, 

 p. 101), and in the current number of the same pub- 

 lication (vol. 82, p. 479) Dr. Halm now clearly shows 

 that " the same law of rotation of the reversing layer 

 can be expected only under similar conditions of 

 activity." He shows a very impressive series of 

 curves, illustrating the angular velocities for about 

 every ten degrees of solar latitude for each year from 

 1901 to 1914, excluding 1910. In these the angular 

 velocity increases rapidly from sunspot minimum 

 (1901) to sunspot maximum (1905), and then more 

 slowly decreases to sunspot minimum (1913) ; the 

 amplitude being much more pronounced for high 

 than for low heliographic latitudes. These results 

 are based on observations made at Upsala, Edin- 

 burgh, Mount Wilson, and Ottawa. 



Sunspot in High Latitude. — A small sunspot was 

 noted at Mt. Wilson on June 24 in latitude 31° north, 

 longitude 8° east. No spot has been seen in such a 

 high latitude since December 1919, and it is con- 

 sidered to be the first spot of the new cycle. It will 

 be remembered that the equatorial spots of the 

 expiring cycle continue for a year or more after the 

 commencement of the new one, so that the actual 

 minimum may not be reached till next year. The 

 above spol was of negative polarity, whereas most of 

 the single northern spots in the expiring cycle were 

 positive. This is a further argument, though not a 

 decisive one, for the spot belonging to the new- 

 cycle. 



