October ii, 1917" 



NATURE 



115 



Manuring for Higher Crop Production, 

 Lussell. 



Dr. E. J. 



A BOOK which should be of interest and value is 

 imounced by the Chisvvick Press, viz. "The Ancient 

 i^arthworks of the New Forest," described and 

 delineated in plans founded on the 25-in. -to-one-mile 

 Ordnance Survey, with a coloured map showing the 

 physical features of the ancient sites of the New Forest 

 founded on the i-in.-to-one-mile Ordnance Survey, by 

 H. Sumner. 



Messrs. Longmans and Co. announce a new edition 

 lit Sir W. Crookes's "The Wheat Problem," contain- 

 mg an additional chapter on " Future'Wheat Supplies," 

 by Sir R. H. Rew, and an introduction by Lord 

 Rhondda. 



OUR ASTRONOMICAL COLUMN. 

 Ephemeris of Encke's Comet. — The following 

 ephemeris of Encke's comet, which is due at perihelion 

 on March 25, 1918, is given by M. Viljev : — 



R.A. Decl. Log t Log A 



1917 



ti. m. s. 



Oct. II 23 41 24 



15 34 ^7 

 ly ^7 45 



23 21 24 



27 15 29 

 31 ro 2 



Nov. 4 5 12 



ii 23 o 53 



12 22 57 12 



16 54 13 

 20 51 S3 



24 50 9 



28 49 o 

 Dec. 2 48 27 



6 48 29 



10 49 3 



14 50 8 



18 51 45 



22 53 50 



26 56 22 



30 22 59 19 



10 17-5 



9 37-9 



8 =7-2 



8 "16-4 



7 36- 1 



01732 

 03757 0-1674 



0-3473 



01670 



01709 



o- 1 780 

 03145 01869 



0-1964 

 0-2762 0-2054 



0-2130 

 0-2307 0-2188 



0-2218 



6 19-7 



5 44-7 



5 12-6 



4 43-6 



4 18-0 



3 560 



3 37-6 



3 22-9 



3 11-7 



3 4-2 



3 0-3 



2 59-9 



3 2-9 

 3 9-2 



+ 3 18-6 



The New Star in N.G.C. 6946.— A further account 

 of the new star discovered by Ritchey in the spiral 

 nebula N.G.C. 6946 (H. iv. 76 Cephei) has been given 

 by Dr. Max Wolf {Astronomische Nachrichten, 

 No. 4902), including a reproduction of a photograph 

 taken with the Konigstuhl reflector on August 21. The 

 region is very rich in faint stars, but the only B.D. star 

 in the neighbourhood is +59° 2662, magnitude 95, 

 which is slightly preceding, and about 7' north of the 

 centre of the nebula. The nova was identified by 

 comparison with earlier photographs of the nebula, and 

 its estimated position, for 1917-0, was R.A. 2oh. 33m. 

 3-is., declination +59° 50' 15". The central star of 

 the nebula follows the nova by about 4-05S., and is 

 105" to the north. On August 2'i the magnitude of the 

 nova was estimated to be 135; on the photograph re- 

 produced it appears to be less bright than the central 

 star, but this is an illusion produced by the nebulosity 

 about the latter, as in photographs taken with short 

 exposures the nova was considerably the brighter. The 

 nebula extends about 6' to 7' in the direction east and 

 west, and the spirals exhibit a very complex knotted 

 structure. The nova is situated near the southern end 

 of an arm which runs obliquely from east to south 

 of the central star. It was not possible fo photograph 

 the spectrum of the nova on account of the feeble 

 luminosity. 



NO. 



2502, VOL. 100] 



WORK-HARDENED MEIALS. 



ONE of the most interesting of the papers presented 

 at the autumn meeting of the Institute of 

 Metals was that by Prof. Jeffries, of the Case School 

 of Applied Science, Cleveland, U.S.A. Hanriot came 

 to the conclusion in 1912 that metals subjected to very 

 high hydrostatic pressures, of the order of 10,000 kilo- 

 grams per square centimetre, even though they under- 

 went no change of shape, showed an increase of hard- 

 ness (Brinell test). Although cubes of silver, copper, 

 and aluminium showed a considerable increase of 

 ball-hardness in these experiments, he decided that in 

 no case were thev appreciably deformed, and that the 

 pressure was sufficient for hard-hammering the metals 

 without deformation. Prof. Jeffries reviews this work, 

 and has repeated the experiments. Tests were carried 

 out by Dr. Bridgman with pure aluminium and an 

 alloy containing SS per cent, of aluminium and 12 per 

 cent, of copper, in the form of cylinders 7/16 in. 

 diameter by ^ in. long, the dimensions of which were 

 accurately measured. The tensile strengths and 

 scleroscope hardness values of the materials were 

 determined with the following results : — 



Tensile stress Scleroscope 



lb. per sq. in. hardness 



Aluminium ... I4>890 ... 6^5 



Aluminium-copper alloy ... 3i,95o ... 24*0 

 Cylinders of each kind of metal were then exposed 

 to a maximum pressure of 12,400 kg. per sq. cm. at 

 25° C, the transmitting liquid being petroleum ether 

 mixed with kerosene. The pressure was maintained 

 at the maximum ^or twenty minutes, and the total 

 period of the test was about 2^ hours. The cylinders 

 were then measured and found to be unaltered in 

 size, and the following results were obtained in the 

 subsequent tests : 



Tensile stress Scleroscope 



lb. per sq. in. hardness 



Aluminium i4i3oo ••• 65 



Aluminium-copper alloy ... 27,300 ... 240 

 In the case of the alloy the threads were stripped 

 at the stress specified, and the specimen was un- 

 broken. Similar experiments at 40° C, using kero- 

 sene alone as the transmitting medium, gave a similar 

 result, except for a slight increase of tenacity, and 

 no alteration in structure was observed. These results 

 contradict those of Hanriot, who found a 30 per cent, 

 increase of ball-hardness in the case of aluminium 

 under a hydrostatic pressure lower than the above. 

 Bridgman directs attention to the fact that Hanriot 

 used vaseline to transmit the pressure, and that this 

 freezes hard under pressure, so that at the higher 

 pressures the stress applied was not hydrostatic. This 

 explanation is plausible. Prof. Jeffries concludes from 

 these and other tests that the hardness of metals 

 cannot be increased without permanent deformations 

 unless such an* increase in hardness is due to an 

 allotropic change. The latter might, of course, cause 

 either an increase or a decrease in hardness. As all 

 Hanriot's results pointed to an increase of hardness it 

 is probable that there was slight permanent deforma- 

 tion which he did not detect, and that this was the 

 immediate cause of the increase. * 



In spite of the large number of researches which 

 have been carried out, both on the purely scientific 

 and technical aspects of the annealing ' of work- 

 hardened metals and alloys, the subject still presents 

 features which require more detailed investigation than 

 they have yet received. The laws of annealing are 

 considerably more complicated than the early investi- 

 gators suspected. Especially does this apply to the 

 first effects liable to be produced by heating. ' That in 

 certain cases a hardening of the' metal or alloy is 

 produced, as measured by the tensile and ball-hardness 



