5o6 



NATURE 



[January 7, 19 15 



It is certainly a remarkable object, as on a com- 

 parison with the list of meteorites recorded in Great 

 Britain, published in the British Museum Guide to 

 Meteorites, there is only one given of greater weight, 

 that fell at Wold Cottage in Yorkshire in 1795. 



The outer coating, which varies from a very thin 

 film to nearly 2 mm. in thickness, presents a very 

 finely-pitted surface, with evidence of a tendency to 

 show lines of movement, as though the heated skin 

 was being pushed backwards from the direction of 

 motion. The portions which had become fused 

 showed a dark glazed or shiny surface, this evi- 

 dently being the forward end, and the portion to 

 which the heat from the compressed air in front of it 

 was most efTective. The appearance of the pittings 

 suggest that the heating of the surface was the means 

 of liberating some portions of the structure of the 

 mass, and that these would provide what is seen as 

 the trail of the meteor after it has passed in its flight 

 through the air, being the continued glow of the 

 heated emissions by combination with the oxygen in 

 the air. 

 • There is evidence that some portions of the surface 



expected from the mineralogical contents. A m.'l^- 

 netic examination of the mass as a whole gavi m 

 appreciable effect, although a search amongst ihc 

 dust which accumulated from the rubbing of the two 

 pieces, indicated portions of magnetic nature though 

 small in amount which proved to be metallic iron. 



The pyritic material contains nickel as well as iron, 

 portions being crystalline, the olivine being of a pale 

 3'ellowish-green colour, whilst the enstatite is whitish 

 or grey. 



The proportions of the minerals worked out on the 

 basis of the composition and solubility are approxi- 

 mately : — • 



Pyritic and metallic matter ... ... 5-07 



Enstatite 31-5 



Olivine ... 6343 



The analysis which has been made by Mr. E. L. 

 Rhead indicate the presence of the following in order 

 of amount : — 



Aptley Bridge Aerolite, October 13, 1914. 



had only come into contact with the air during the 

 later portion of its traverse. These regions have all 

 the appearance of flakes of the outer skin having 

 been broken away, a slight tarnishing of the pyrites, 

 if at a distance from the edge of the fracture or 

 slight fusing when close to the general outer coating, 

 indicating a removal of portions of outer layers of 

 the mass. 



This is quite in keeping with the assumption that 

 the fragments were split off at the time of the 

 apparent burst in the air, at about twenty miles' 

 altitude, as from that position the speed of the meteor 

 would be so much reduced by the compressional 

 friction, that it would be losing more heat than 

 gaining. 



The fractured surface on an inspection appeared 

 to be made up of a glittering mass of white and 

 yellow points in a grey setting. These proved to be 

 chiefly pyrites, and their presence accounted for the 

 apparent great weight according to the size. The ! 

 specific gravity of the mass determined from a frag- i 

 ment was 333, and is in accord with what would be I 



NO. 2358, VOL. 94] 



The accompanying illustration shows the front view 

 of the aerolite with the thumb marks. 



WiLLi.AM C. Jenkins. 

 II Upper Lloyd Street, Moss Side, Manchester, 

 December 27, 1914. 



A Suggested Definition of Magnetic " Permanence." 



From time to time accounts appear of experiments 

 on new kinds of steel which have been undertaken 

 with the object of determining the most suitable 

 material from which to construct a permanent mag- 

 net. Experiments of my own on this subject, made 

 a good many years ago, led me to think that it would 

 be an advantage if precision could be given to the 

 term "permanence" in magnetism, and inasmuch as 

 a high coercive force is the principal factor in the 

 preservation of the magnetism in a magnet the 

 measure of permanence , I think, might be talcen as 

 the coercive force per unit of residual magnetic in- 

 tensity. Thus the inclination of the intensit5--field 

 curve as it falls from residual to zero intensity indi- 

 cates what the permanence of the magnet may be 

 expected to be. 



According to this definition the permanence of soft 

 iron is about 00024. Recent experiments by Miss 

 Margaret Moir (Phil. Mag., Nov^ember, 1914) on 

 chrome steel give the high permanence of 0-165, or, if 

 the calculation is made from final residual magnetism 

 after shocks and changes of temperature, of 0-201. 

 These examples show a range of permanence from 

 0-0024 to 0-201, in the ratio of i to 84, but it is not 

 unlikely that these limits may be exceeded. 



J. R. ASHWORTH. 



55 King Street South, Rochdale'. 



EUROPEAN AERODYNAMICAL 

 LABORATORIES.^ 



IN the summer of 191 3 Prof. Zahm and Lieu- 

 tenant Hunsaker, of the United States, visited 

 the European aerodynamical laboratories in order 

 to study apparatus and methods in use, before 

 finally deciding- on the details of the material to be 



1 Report on European Aeronautical Laboratories. By Dr. A. F. Zahm. 

 Smithsonian Miscellaneous Collections, vol. Ixii., No. 3. (Washington : 

 Snkithsonian Institution, 1914.) 



