June 23, 1921] 



NATURE 



535 



head is equal to the pressure of fluidity. Unquestion- 

 ably the most interesting of Mr. Ackermann's results 

 is that clay possesses a pressure of fluidity at which 

 the loaded pile sinks through the clay without further 

 increase in the load. This critical pressure depends 

 upon the percentage of water present, being greater 

 with less water. Mr. Ackermann has added to his 

 former work in the direction of experiments designed 

 to separate the work done against frictional resist- 

 ances from that done in displacing the clay, and 

 finds that the former is by far the larger quantity. 

 A number of experiments have also been made on 

 chalk, and the author finds that wet powdered chalk 

 has a modified pressure of fluidity, and that the water- 

 content affects greatly the properties of chalk. There 

 is a marked diff'erence in the physical properties of 

 powdered chalk as compared with precipitated chalk. 

 The adhesion and cohesion of wet chalk are much 

 less than those of clay ; clay is hygroscopic and chalk 

 is not. 



The Daily Mail of June 13 published an article 

 by a scientific correspondent under the sub-heading 



"Can Eyes Radiate Energy?" which gives some 

 account of a new instrument showing that " rays pro- 

 ceed from the eye which are capable of being regis- 

 tered just as wireless messages are detected." Dr. 

 Charles Russ, the inventor of the instrument, writes 

 to us stating that the paragraph constitutes a breach 

 of confidence on the part of someone to whom the 

 instrument was shown. It was intended that the 

 phenomenon should be announced at the Ophthalmo- 

 j logical Congress at Oxford on July 7, and some annoy- 

 I ance has been caused to Dr. Russ by this premature 

 1 disclosure. 



Mr. a. Risdon Palmer is bringing out through 

 Messrs. George Bell and Sons, Ltd., a series of 

 Handbooks of Commerce and Finance planned to 

 j meet the need of a simple and graphic presentation 

 of the fundamental principles of commerce and 

 i finance. The first three volumes, dealing respectively 

 j with ■■ Transport and the Export Trade," "The Im- 

 port Trade : Mixing Commodities," and "The Use of 

 Graphs in Commerce and Industry," will be ready 

 shortly. 



Our Astronomical Column. 



The Meteoric Radiants of June 25-30. — Mr. 

 Denning writes : — The possible occurrence of an 

 abundant meteor shower from Pons-Winnecke's 

 comet will attract a great number of astronomical 

 observers to watch the heavens. The moon will rise 

 late, and, being at her last quarter, will not offer any 

 serious impediment to observation. 



There are a considerable number of radiant points 

 visible at this period of the year, though the usual 

 rate of apparition is not nearly so great as in the 

 two following months of July and August. 



The great shower of Perseids probably begins at the 

 end of June, apd the radiant is then situated at about 

 o°+36°. As it may prove useful for reference, a list 

 of the principal radiant points observed in past years 

 between June 25 and 30 is appended : — 



+ 36 238 + 47 282-12 314 + 61 



24 + 42 245 + 64 282-24 320+11 



30 + 36 260-24 291 + 52 320+,2I 



43 + 37 261-12 291 + 60 334 + 57 



48 + 44 261+ 4 294 + 40 334 + 28 



161 + 58 263 + 63 304 + 23 342 + 39 



193 + 57 270 + 47 305-12 354 + 39 



213 + 53 270 + 30 314 + 47 354 + 77 



Report of the Kodaikanal Observatory for 1920. — 

 It has already been mentioned in this column that direct 

 comparisons of the solar lines with those of cyanogen 

 and iron gave results fairly near those predicted by 

 Einstein, but since the shifts were different for dif- 

 ferent substances, and also not proportional to the 

 wave-length, they could not be wholly due to a 

 gravitational effect. Tests made on the Venus spec- 

 trum gave further evidence of the shift being in part 

 an "earth effect." A considerable improvement has 

 been effected in the Venus spectra by using " Barnet 

 Ultra Rapid" plates hypersensitised with ammonia; 

 these enabled a very narrow slit to be used. When 

 the terminator was placed normal to the slit, no evi- 

 dence was obtained of an inclination of the spectral 

 lines due to rotation of the planet. A recent letter 

 from the director states that further photographs will 

 be taken to test the rotation in sixty-eight hours about 

 a highly inclined axis that was recently provisionally 



NO. 2695, VOL. 107] 



I announced by Prof. W. H. Pickering. It was found 

 ! that change of altitude produced no change in the 

 j wave-lengths in the Venus spectra, the range of alti- 

 I tude extending from below 20° to above 40°. 

 ; The use of an ultra-violet spectrograph with a 

 quartz collimating lens demonstrated the solar origin 

 i of the ammonia band in the solar spectrum at A3360, 

 i since the rotation shift between the east and west 

 [ limbs was shown. 



i The spot activity, as indicated by the number of 

 groups, diminished 40 per cent, in 1920 as compared 

 with 1919. It is noteworthy that the spot group 

 associated with the great magnetic storm of 1920 

 March 22-23 returned five times (1920 January to 

 May), there being a magnetic storm on each occasion. 

 Unlike the spots, there was an increase in both 

 prominences and hydrogen absorption markings as 

 compared with 1919. A great eruptive prominence 

 seen in 1920 December 31 strongly resembled that 

 seen in the eclipse of 19 19 May. A continuous series 

 of spectrograms was secured, which showed the pro- 

 minency matter ascending rapidly and fading away 

 at a height of 16' above the limb. 



Popular Astronomy in Sweden. — We have already 

 directed attention to the Popular Astronomisk Tid- 

 shrift; Hafte i o. 2, 192 1, is another number full of 

 I interest. We may refer specially to an illustrated 

 I article by V, Carlheim-Gyllenskold on Tycho Brahe 

 j and his observatory on the island of Hven ; many 

 i photographs of the present aspect of the latter are 

 given, showing- that it is still possible to trace out the 

 outlines of the foundations of all the building's and 

 instruments. A portrait of Tycho Brahe and a photo- 

 graph of the house where he was born are also repro 

 duced, together with many relics unearthed from the 

 ruins. 



The latitude of Sweden favours observations of 

 auroras, which are made systematically at several 

 stations. The aurorae of September 28 and 

 October 17, 1920, are described in detail, with dia- 

 grams indicating- the exact locations of auroral 

 streamers among' the stars. 



