July 8, 1920] 



NATURE 



595 



Our Astronomical Column. 



Commencement of the Grej\t Perseid Shower of 

 Meteors. — The first Perseids probably appear at the 

 end of June. They have certainly been observed in 

 the first week of July. The earliest meteor of this 

 shower, which has been doubly observed and the real 

 path of which has been computed, was seen on July 8, 

 1918, by Mrs. Fiammetta Wilson and Miss A. Grace 

 Cook. ' This year the moon left the evening sky 

 about July 6, 'and the sky should be watched for 

 traces of oncoming Perseids. At this time of the year 

 meteors generally increase in numbers, and especially 

 after the middle of July. The Perseids gradually 

 become more abundant, and among the minor displays 

 the chief ones are : 



contributed a paper on this nova to the June meeting 

 of the Royal Astronomical Society which contains 

 some interesting calculations on the rate of expan- 

 sion. It was written before the recent Lick measures, 

 which indicate a mean annual rate of increase of 

 diameter of 1-9", but he notes that Barnard's measures 

 gave an increase of 2" in the first six months, so that 

 the rate may be diminishing. 



Assuming the displacements of the edges of the 

 bands in the spectrum to be a measure of the rate of 

 expansion of the nova into a planetary nebula, Dr. 

 Lunt found a radial velocity of 1500 km. /sec, which 

 would give a diameter of i/ioo light-year in a year, 

 ' and would imply a distance of the nova of 1000 light- 

 years. 



According to Van Maanen's parallax of the ring 

 nebula in Lyra (the largest nebula on his list), its 

 diameter is o-i6 light-year. The expanding nova 

 would attain this size in sixteen years if the rate were 

 maintained. 



Dr. Lunt notes that in the nova spectrum there are 

 fine dark lines close to the normal positions of the 

 H and K lines of calcium, which indicate a motion 

 of approach to the sun of 17 km. /sec, exactly the 

 amount due to the sun's own motion. A similar 

 feature has been noted in several other stars, and 

 the suggestion made that these lines arise from 

 clouds of very tenuous calcium vapour at rest in 

 space. On this view these lines exist in the spectra 

 of most stars, but are hidden by the star's own lines 

 unless the latter are shifted by a large radial motion. 



The New Minor Planet GM. — It will be remem- 

 bered that last January Senor Comas Sola, of Barce- 

 lona, discovered a new minor planet which was much 

 brighter than most of those discovered in recent years, 

 and was taken for a cofnet by some observers. The 

 object was very well observed for several months, so 

 that an accurate determination of the orbit is possible, 

 and there is not much fear of its being lost again, as 

 has happened to many of these little planets. -The 

 discoverer has now given it the name " Alphonsina," 

 in double homage, as he says, to Alphonso X. of 

 Spain, who was known as "the Savant," and to the 

 present king, Alphonso XIII. 



NO. 2645, VOL. 105] 



Annual Visitation of the National Physical 

 Laboratory. 



O' 



N the occasion of the visitation of the National 

 Physical Laboratory by the General Board on 

 June 22, a large number of distinguished visitors 

 availed themselves of the opportunity of inspecting 

 the laboratory. The visitors were received by the 

 chairman of the board (Sir Joseph J. Thomson) in 

 the 7-ft. wind channel of the new aeronautics build- 

 ing, and afterwards visited the various departments 

 ot the laboratory, where exhibits illustrative of recent 

 work were on view. 



The exhibit in the engineering department was 

 noticeable for the large number ot machines for test- 

 ing resistance to shock and to fatigue. The day is 

 past when a simple test in tension is considered 

 to yield sufficient dat& for structural material, 

 and many other forms of test are now in use. One 

 machine, designed by Dr. B. Haigh, subjects the 

 specimen, by means of an alternating magnetic flux, 

 to a maximum load of ±075 ton reversed two 

 thousand times every minute. Another instrument, 

 designed and constructed in the department, tests the 

 endurance of stranded cables passing over pulleys. 

 Among the impact testing machines, many of which 

 were designed and made in the department, mention 

 may be made of one in which both hammer and anvil 

 are swung; by this means it is possible to obtain a 

 striking velocity as high as 43 ft. per second. 

 Machines for measuring the elastic limits of materials 

 at high temperatures and for determining the efficiency 

 of chains, gears, etc., were also among the exhibits. 



In the aeronautics department various wind channels 

 were operating, measurements of the performance of 

 air-screws, the effects of aeroplane bodies on screws, 

 and stability tests on bodies being carried out. Ap- 

 paratus for measuring the skin-friction of air passing 

 over thin plates was also exhibited. 



Amongst the exhibits in the metallurgy department 

 were a number of examples of failures of steel and 

 alloy articles which had been sent in for investigation. 

 Photomicrographs illustrating sections from these, as 

 well as various sections under the microscope, were 

 shown. 



The representation of the constitution of a series of 

 ternary alloys has never been an easy matter. 

 Three models were exhibited which are designed 

 to overcome this difficulty. They represent parts of 

 the "diagram " for copper-aluminium-zinc alloys and 

 a part of the aluminium-magnesium-silicon "dia- 

 gram," 



Considerable improvement has recently been intro- 

 duced into the manufacture of thin-walled refractory 

 tubing for thermo-couple protection and insulation ; 

 the apparatus with which it is made was shown in 

 operation. 



Demonstrations of the rolling of manganin, cast 

 at the laboratory, into rods prior to wire-drawing 

 were given in the rolling mill. Much valuable work 

 has been done, in conjunction with the electricity 

 department, on this metal, and it is now possible 

 to produce manganin wire equal to the best pre-war 

 material which was imported from Germany. 



k modified form of the Shakespeare katharometer, 

 used for measuring the permeability of balloon fabric, 

 was in operation in the aeronautical chemistry 

 division. 



The exhibits in the Frpude national tank can be 

 divided into three heads. The first dealt with tests 

 on the trim, the longitudinal stability, and the resist- 

 ance of hulls of flying-boats. The second was work 

 which was being carried out for Lloyd's Register in 



