112 W. H. HOBBS — METEORITE FROM ALGOMA, WISCONSIN 



for the chemical anal3^sis, and to Professor A. C. Scott, of the Rhode 

 Islafid Agricultural College, at present Honorary Fellow of the Univer- 

 sity of Wisconsin, for some very successful photographs. To Mr Richard 

 Runke, who supplied the material for study and who has devoted con- 

 siderable time to search for separated fragments of the meteorite, the 

 Universit}^ of Wisconsin and the writer have been placed under obliga- 

 tion. From the Field Columbian Museum and Professor 0. C. Farring- 

 ton, the curator of its collection of meteorites, the writer has received 

 many courtesies. 



Appendix: Discussion of the Motions of a Discoid Meteorite; 

 BY Charles S. Slichter 



In the following discussion the attempt is made to explain by simple 

 and w^ell known principles of mechanics the motions of the Algoma 

 meteorite after it had reached the earth's aerosphere. It is assumed that 

 the meteorite arrived at the outer limits of the air with a high velocity 

 of translation and a high rate of rotation about its shortest principal 

 axis. According to the well known laws of motion of a rigid bod}^ onh" 

 two of the three principal geometrical dimensions of the meteorite would 

 be stable axes of rotation, namel}^ the longest and the shortest of its 

 geometrical axes. The meteorite being thin and flat in shape, the direc- 

 tions through the center of mass in which an initial axis of rotation 

 could lie and result in stable rotation about the long axis are exceed- 

 ingly limited in range, so that rotation about the long axis would be 

 very unlikely, even early in the histor3\ We must therefore suppose 

 that rotation took place about the axis of greatest stability, which is the 

 shortest axis of the body. If the meteorite were not so flat and elon- 

 gated it possibly would not be so essential to suppose that its rotation 

 was about its shortest axis. We must also assume that the axis of the 

 meteorite made an angle S with the direction of its path, whose value, 

 when the aerosphere was reached, ma}^ have been an}^ chance amount 

 whatsoever. 



We shall first consider the distribution of the pressure of the air upon 

 the surface of the meteorite. The lines of motion of the air particles 

 past the moving meteorite are shown approximately by the curved lines 

 in figure 4. 



This drawing is based on a diagram of Lord Rayleigh,^ who has 

 presented the results of a mathematical investigation of the stream lines 



*See Kirchoff: Zur Theorie freier Flussigkeitsstrahlen, Crelle, vol. Ixx, 1869; Lord Rayleigh : 

 On the resistance of fluids, Phil. Mag., December, 1876; Lamb: Hydrodynamics, 1895, pp. 94, 

 109-111. 



