574 



NA TURE 



[April 14, 1887 



Mr. T. B. Mackintosh has kindly analysed a small fragment 

 with the following results, which, for comparison with other 

 irons seen to fall, 1 have placed in tabular form : — 



Mazapil. Rowlon. Cliarlotte. Estherville.' 



Flight. Smith. Smith. 



Iron 91-260 91-250 91-15 92-oco 



Nickel 7-845 8-582 S-05 7-100 



Cobalt 0-653 o'37' °'72 0-690 



Phosphorus... 0-300 oo5 o-U2 



100-05S 100-203 99 "98 99-902 



Carbon is distributed all through the iron between the crystal- 

 line plates, and it is noteworthy that this element was observed 

 with the spectroscope as present, in the " Bielids " of November 

 27, 1885. Chlorine is also present and shows itself by a slight 

 superficial deliquescence. Of this latter I will state that most 

 of the surface oxidation of the ferrous chloride has occurred since 

 August last. As yet no tests have been made to ascertain the 

 amount of occluded gases, or to analyse the graphite nodules, 

 and it is probable that this might only lead to results similar to 

 those already obtained. Over the mass, where the crust has been 

 accidentally removed, the lines of crystallisation (Widmanstatten 

 figures) can readily be traced without etching the surface. The 

 abiasion due to impact was very slight. 



In conclusion, we cannot, from the very circumstantial account 

 of the fall, and the corroborative evidence of the iron itself, 

 which in several particulars contains heretofore unrecorded ob- 

 servances, decline to receive this meteorite as the ninth recorded 

 fall of an iron mass to the earth ; and perhaps at another period 

 of the November " Bielids " this fall will be confirmed in all its 

 interesting details. The interest connected with this meteorite, 

 because of its beautifully marked and fresh surface, is enhanced 

 by the concurrence of the time of its fall with the shower of the 

 Biela meteors. 



I wish to express here my deep obligation to Prof. Bonilla for 

 the interesting data concerning this meteorite and for the gift of 

 the meteorite itself, and to Sir. Mackintosh also for his kind 

 interest in making the chemical analysis. 



William Earl Hidden 



SOCIETIES AND ACADEMIES 



London 



Royal Society, March 24. — "On Ellipsoidal Current 

 Sheets." By Horace Lamb, M.A., F.R.S. 



The paper treats of the induction of electric currents in an 

 ellipsoidal sheet of conducting matter whose conductivity per 

 unit area varies as the perpendicular from the centre on the 

 tangent plane, or (say) in a thin shell of uniform material 

 bounded by similiar and coaxial ellipsoids. The method 

 followed is to determine in the first instance the normal types 

 of free currents. 



When the normal types and their persistencies have been 

 found, it is an easy matter to find the currents induced by 

 given varying electromotive forces. Supposing that we have 

 an external magnetic system wliose potential varies as «■•", 

 we can determine a fictitious distribution of current over the 

 shell, which shall produce the same field in the interior. If 

 (|> denote the current-function for that part of the distribution 

 which is of any specified normal type, (J) that of the induced 

 currents of this type, it is shown that 



9 = - — ^ — <?> 



1 + l/T 



where t is the corresponding persistency of free currents. When 

 /t is very great this becomes 



<p = ~ 4,, 

 in accordance with a well-known principle. 



This method can be applied to find the currents induced by 

 rotation of the shell in a constant field, it being known from 

 Maxwell's "Electricity," § 600, that the induced currents are 

 the same if we suppose the conductor to be fixed, and the field 

 to rotate in the opposite direction. When the conductor is sym- 

 metrical above the axis of rotation, the current-function of any 

 normal type contains as a factor cos su or sin soi, where a is the 

 azimuth, and s is integral (or zero). When we apply Maxwell's 

 artifice, the con-esponding time-factor is e'-'^', where fi is the 

 angular velocity of _the rotation ; and we easily find that the 



^ Fell May 10, 1S79, and 

 on surrounded by silicates. 



d embedded nodules of nickeliferi 



system of induced currents of any normal type is fixed in space, 

 but is displaced relatively to the field through an angle, 



I 



- arc tan /'st 

 s 



in azimuth, in the direction of the rotation. 



In the most important normal types the distribution of 

 current over the ellipsoid is one which has been indicated by 

 Maxwell ("Electricity," § 675) as giving a uniform magnetic 

 field throughout the interior. 



In the higher types the current- function (^ is a Lame's func- 

 tion, degenerating into a spherical harmonic when two of the 

 axes of the ellipsoidal shell are equal. Of the special forms 

 which the conductor may assume, the most interesting is that in 

 which the third axis (that of symuietry) is infinitesimal, so that 

 we have practically a circular (fisi, whose resistance p' varies 

 according to the law 



p' = Pu' \' 1 1 - y-jfi^l^ 

 where Pq' is the conductivity at the centre, a is the radius, and r 

 denotes the distance of any point from the centre. In the most 

 persistent type 



This result is of some interest, .as showing that the electrical 

 time-constant for a disk of uniform resistance p,,' must at .all 

 events be considerably less than 4-93 al^^} 



The problem of induced currents is then discussed, more 

 particularly in the case of a circular disk, of the kind indicated, 

 rotating in any constant magnetic field. In view of the physical 

 interest attaching to the question, it would be interesting to have 

 a solution for the case of a uniform disk ; but in the absence of 

 this, the solution for the more special kind of disk here considered 

 may not be uninstructive. 



In the most important types of induced currents, the magnetic 

 potential n due to the field oc xz, so that the lines of force at the 

 disk aie normal to it, but the direction of the force is reversed 

 as we cross the axis of s. The current-function relatively to 

 axes displaced through the proper angle tj in the direction of 

 rotation, varies as 



j'V {'-'>'}• 



In the next type O. == ^{x^ -y'), and the current-function, rela- 

 tively to displaced axes as before, varies as xy \li — r'-jd'. 



" Note to a Memoir on the Theory of Mathematical Form " 

 (Phil. Trans. 1886, vol. clxxvii. p. I). By A. B. Kempe, M.A., 

 F.R.S. 



The object of this note is to make some slight but important 

 amendments of certain sections of the original memoir (viz. sees. 

 5> 7> 73 to 77> ^"d 167), relating to the definition and use of 

 what the author terms " aspects " of collections of things. An 

 "aspect" of a collection of « things is that which is under 

 consideration when to each individual thing of the collection we 

 mentally affix a distinctive degree of prominence or other mark. 

 These « marks may be regarded as interchangeable with each 

 other, and we thus get \n aspects of the collection, of which 

 some are undistinguishable from each other. If the interchanges 

 corresponding to a complete system of undistinguishable aspects of 

 the collection are given we know the " form " of the collection. 



March 31. — " On Clausius's Characteristic Equation for Sub- 

 stances applied to Messrs. Ramsay and Young's Experiments on 

 Alcohol." By Prof. Fitzgerald, Trinity College, Dublin. 



This paper is an investigation of how far Clausius's equation 



!> l_ I 



A't ~ v-a ~ @{Z' + $)- 

 represents accurately Messrs. Ramsay and Young's experimental 

 results. It is shown that, considering the enormous range of 

 values to be represented, it represents the results remarkably 

 accurately, except that from the volume of the liquid, where 

 alone the value of a is of much consequence, it follows that a is 

 not constant, but is a function of both the temperature and 

 pressure. 



The paper contains a short discussion of the geometrical forms 

 of the curves — a particular case of which is represented by this 

 equation. 



^ I find by methods similar to those emplojred by Lord Rayleigh for the 

 approximate determination of various acoustical constants, that the true 

 value lies between ira/p' and 2-26 aip'. For a disk of copper (p=i6oo 

 C.G.S.), whose radius is a decimetre and thickness a millimetre, the lower 

 limit is 0-0014 sec For disks of other dimensions the result will vary as the 

 radius and the thickness conjointly. 



