Dr. Walter Flight — History of Meteorites. 313 



sharp and regular were they, that they resembled lines described on 

 paper with a drawing pen. When magnified 200 to 300 diameters, 

 they appeared to be tubes, sometimes empty, sometimes filled 

 more or less with a black or light grey substance, or both substances. 

 In one crystal with two small faces 7c, and between them the face a, 

 it was noticed that the faces a and the tubes reflect light at the same 

 instant, and that they lie at right angles to the axis of the zone Tea. 



Von Kokscharow found these canals in every granule of the Pallas 

 olivine which he examined ; one crystal, 6 mm. in diameter, through 

 which a section was cut, exhibited 17 of them under a pocket lens, 

 and many more in the microscope ; they were all parallel to the 

 edge s r, that is to say, parallel to the vertical crystallographic axis. 

 A mean of nine measurements of the angle which these canals form 

 with the edge ea (which were made with a very good goniometer, 

 designed by von Auerbach and constructed by Hartnack) was found 

 to be 38° 28', the calculated angle being 38° 27' 12". The plane of 

 the optic axes lies at right angles to the canals, and therefore to the 

 crystallographic vertical axis ; in short, this plane in Pallas olivine, 

 as in the terrestrial specimens, is parallel to the basal pinacoid c = 

 oP. 



The canals were studied in seven sections of crystals, and drawings 

 of them are given in a plate. By altering the focus of the micro- 

 scope, canals lying at various depths are brought into view ; when 

 a certain thickness of the olivine has been traversed, the doubly- 

 refractive power of the intervening layer of the mineral causes the 

 canals to appear double. Another effect of this property of the 

 crystal is that the magnifying power of the microscope is also 

 apparently somewhat increased. The partial overlapping of the two 

 images of a canal gives it the appearance of a tube filled throughout 

 the entire length with black material ; others, again, viewed through 

 greater thicknesses of the mineral, appear as two distinct tubes. 

 Examination with a Nicol or a tourmaline plate at once convinces the 

 observer that these effects are due to double refraction. 



The enclosed black and grey matter is found sometimes at one end 

 only of a tube, sometimes in the middle, or again at different points 

 in its length, in which case it presents the appearance of a ther- 

 mometer, the mercurial column of which has been broken. Other 

 sections are described which were prepared so that the tubes were 

 cut obliquely, or at right angles. The results of an examination of 

 these sections in polarized light supports the assumption that these 

 appearances are caused by hollows traversing the olivine, and not by 

 transparent crystals enclosed in it. 1 



This olivine has been investigated chemically by Howard, Klap- 

 l'oth, Stromeyer, Walmstedt, and Berzelius. It has recently been 



1 It should be mentioned that Rose (Beschr. und Einth. Met., 76) found these 

 canals in great perfection and abundance in the olivine of the meteorite found at 

 Brahin, Minsk, Russia (1810), a siderolite bearing the closest resemblance to the 

 Pallas iron. The mineral occurring in tbe siderolites of Rittersgriin and Steinbach, 

 which Rose termed olivine, and some of the angles of which he found to accord with 

 those of the olivine of the Pallas and Brahin siderolites, is probably not olivine, but 

 bronzite. 



