ii6 



NATURE 



[October ii, 1917 



tests, must be regarded as established by the work of 

 Charpy, Bengough and Hudson, Mathewson and 

 Fhilhps and 'ihompson. Moreover, according to Howe, 

 the first effect of slight heating in the case of iron 

 may be either a softening or a hardening, depending 

 on the intensity of the previous deformation, and in 

 his view at least two agencies are at work in pro- 

 ducing these results. 



Prof. Carpenter and Mr. Taverner, of the Royal 

 School of Mines, have investigated the way in which 

 the tenacity of cold-worked aluminium of one par- 

 ticular degree of hardness is affected after the -applica- 

 tion of heat at various temperatures, and for periods 

 of time very much longer than any that have been 

 employed in any previous investigations. They find 

 that the effect of heat at temperatures from 

 55o°-3oo" C. inclusive is to cause a very rapid soften- 

 ing of the metal, and that the same ultimate value of 

 tenacity is reached in all cases. Softening is complete 

 in ninety-six hours, and nearly the whole of this 

 occurs in the first hour of the test. At 250° C.the 

 rate of softening, while still considerable, is much less 

 ; rapid. Between 600 and 800 hours are required for 



■ complete softening, and here also the same ultimate 



i value of tenacity is reached as at higher temperatures. 



i From 200° to 100" C. inclusive the rate of softening 



' is slow, and as the temperature of 100'' is approached, 



very slow. The actual sequence of changes can be 

 classified conveniently under three heads : — (i) A com- 

 paratively rapid drop in tenacity in the first hour. 

 (2) A tendency either to cease falling or actually to 

 rise, such rise, in one case only, bringing the tenacity 

 up to the original value. This period is in most cases 

 completed in about 100 hours. (3) _A relatively very 

 slow fall of tenacity which is maintained on the whole 

 steadily. These tests are still in progress. Assum- 

 ing the present rate of loss of work-hardness to be 

 maintained, and that the metal ultimately reaches the 

 same tenacity as specimens tested at the higher tem- 

 peratures, periods of the order of from one to three 

 vears will be required for completion. The fluctua- 

 tions in the tenacity values referred to under (2) appear 

 to be well established. Similar fluctuations in the rate 

 of solution of hard-worked aluminium-sheet had pre- 

 viously been recorded by Seligman and Williams. 

 The authors have also shown that the cold-rolled 

 aluminium loses a considerable part of its work-hard- 

 ness, in the temperature range 200° to 100° C, with 

 scarcely any recovery of plasticity as judged by the 

 elongation test. H. C. H. C. 



BRILLIANT FIREBALL OF OCTOBER i. 



METEORS of the largest type exhibit a propensity 

 to appear in the twilight of early evening. On 

 Monday, October i, at 6.37 p.m., a splendid object of 

 this class presented itself, moving slowly along an 

 extended flight in a south to north (direction.. It was 

 observed by a large number of persons in various parts 

 of the country, and descriptions have been received 

 from places so wide apart as Weston-super-Mare, 

 Somerset, and the extreme North of England. 

 ^ The accounts to hand are not, as usual in such 

 cases, in perfect agreement, but some of them are 

 excellent, and form a good basis for determining the 

 meteor's real path in the air. The Rev. Canon J. M. 

 Wilson observed the meteor from Worcester, , and de- 

 scribes its flight as from 40° E. of N., alt. 15° to 18°, to 

 5° E. of N., and alt. 5°. Duration about 25 sec. for 

 the section of path he viewed. The Rev. J. Dunn, of 

 Weston-super-Mare, describes the fireball as very bril- 

 liant, passing just above Capella. It was visible for 

 : five seconds ; the head was some ten minutes of arc In 

 diameter, and it threw off a short, reddish trail of 



NO. 2502, VOL. 100] 



sparks. Mr. H. J. Woodall saw the fireball from 

 Oldham, and says it was in a direction 9° N. of E., 

 and falling towards N. at an angle of 30°. The Rev. 

 Watson Stratton, writing from Goole, Yorks, givts 

 the path as from N.N.E., nearly as high as Polaris, 

 to a point a few degrees W. of N., and about alt. 12°. 

 Mr. Philip Burtt was at Penrith Station, and viewed 

 the meteor as it descended and terminated its career 

 just to the right of the moon. It was of a rich yellow 

 colour. Mr. T. J. Moore reports from Doncaster thai 

 the direction was from E.N.E. to N.N.W., and that 

 about one minute after the object had passed a very 

 loud explosion was heard. 



Many other accounts from Liverpool, Grantham 

 (Notts), and other places might be quoted. Spectators 

 agree as to the remarkable brilliancy of the object, and 

 state that it aroused apprehension in cases where its 

 real nature was not understood. 



I have computed the real path as follows : — 



Height at appearance, 56 miles over 4 miles E. of 

 Boston, Lincolnshire. ■ 



Height at disappearance, 19 miles over 15 miles N. 

 of Stanhope, Durham. 



Length of luminous course, 160 miles. 



Velocity per second, 23 miles. 



Radiant point, 320° — 22° in Capricornus. 



The Rev. J. Dunn's estimate of the diameter would 

 give the dimensions as half a mile, but this included 

 the flaming effect and glare. Probably the solid 

 nucleus was not many inches in diameter. As to the 

 sound heard at Doncaster, it came too quickly for it 

 to have been a meteoric effect. 



Another fireball was seen on September 23. It lit up 

 the sky, and was directed from a radiant at about 

 322° — 23°, and probably belonged to the same system 

 as the more recent one of October i. Observations of 

 the latter are still coming in, and it may be found 

 desirable slightly to alter the results above given. A 

 second fireball was seen on the same night at 10.46. 

 Its radiant appears to have been at 351° + 2°, and its 

 height seventy-six to fcrty-one miles. 



W, F. Denning. 



THE TASK OF BRITISH AGRICULTURE. 

 'T^HE speech of the President of the Board of Agri- 



-*• culture at Darlington on October 5 calls for the 

 widest attention as an authoritative pronouncement on 

 the present situation of British agriculture in relation 

 to the need for increased food production. The 

 exigencies of a long war have imposed upon the 

 British farmer the duty, on one hand, of securing a 

 greatly increased production of bread-corn and pota- 

 toes, and, on the other, of maintaining the supplies 

 of milk and meat. The ideal placed before him by 

 the Board of Agriculture in the first place is an in- 

 crease of 3,000,000 acres under grain, potatoes, and 

 roots, to be obtained partly from existing arable land 

 and partly by ploughing up pasture. To secure this 

 end the Government is prepared to help, and Mr. 

 Prothero outlined how much has already been done in 

 the way of guaranteed prices for corn, extension of 

 credit facilities, supply of soldier and women labour, 

 increased supplies and controlled prices of fertilisers, 

 supply of horses, ploughs, and ploughmen, and further 

 of mechanical tractors. Of the last-named 1500 are 

 already at work, and it is hoped that by February next 

 the number will have increased more than fourfold. 

 A timely warning was given, however, that the tractor 

 in its present sta^e of development must be regarded 

 as the least efficient of ploughing implements, and 

 should be used preferably for the lightest work. 



On the question of the maintenance of the milk 

 supply Mr. Prothero urged that with the reasonable 



