532 



NA TURE 



[Sept. 2j, 



iron is found on the periphery of meteorites of native iron, and 

 its presence is readily understood when we admit their cosmic 

 origin. Indeed these meteoric particles of native iron, in their 

 transit through the air, must undergo combustion, and, like 

 small portions of iron from a smith's anvil, be transformed 

 either entirely or at the surface only into magnetic oxide, and 

 in this latter case the nucleus is protected from further oxidation 

 by the coating which thus covers it." 



We are next shown that these metallic chondroi occur with stony 

 chondroi, so that if the interpretation of a cosmic origin for the 

 magnetic spherules with a metallic centre be not considered 

 established in a manner absolutely beyond question, it almost 

 becomes so when we take into account their association with the 

 silicate spherules, never found in rocks of a terrestrial origin. 

 These are thus described : — 



"Among the fragments attracted by the magnet in deep-sea 

 deposits we distinguish granules slightly larger than the spherules 

 with the shining black coating above described. These are 

 yellowish-brown, with a bronze-like lustre, and under the micro- 

 scope it is noticed that the surface, instead of being quite 

 smooth, is grooved by thin lamellae. In size they never exceed 

 a millimetre, generally they are about 0*5 millimetre in diameter ; 

 they are never perfect spheres, as in the case of the black 

 spherules with a metallic centre ; and sometimes a depression 

 more or less marked is to be observed in the periphery. When 

 examined by the microscope, we observe that the lamellae which 

 compose them are applied the one against the other, and have 

 a radial eccentric disposition. It is the leafy radial structure 

 (radialbldttrig), like that of the chondres of bronzite, which pre- 

 dominates in our preparations. We have observed much less 

 rarely the serial structure of the chondres with olivine, and 

 indeed there is some doubt about the indications of this last 

 type of structure. Fig. 6 shows the characters and texture of 

 one of these spherules magnified twenty-five diameters." 



Fig. 6. — Chondros. Spherule of bronzite (25 : 1) from 3500 fathoms in the 

 Central South Pacific, showing many of the peculiarities belonging to 

 chondres of bronzite or enstatite. 



It is worthy of remark that, associated with these chondroi in 

 the red muds at the greatest depths in the ocean, are found 

 manganese nodules in enormous numbers. If a section be made 

 of one of these, a number of concentric layers will be observed 

 arranged around a central nucleus — the same as in a urinary 

 calculus. When the peroxide of manganese is removed by 

 strong hydrochloric acid, there remains a clayey skeleton which 

 still more strongly resembles a urinary calculus, according to 

 Mr. Murray. 



This skeleton contains crystals of olivine, quartz, augite, mag- 

 netite, or any other materials which were contained in the clay 

 from which the nodule was taken. In the process of its deposi- 

 tion around a nucleus, the peroxide of manganese has inclosed 

 and incorporated in the nodule the clay and crystals and other 

 materials in which the nucleus was embedded. The clayey 

 skeleton thus varies with the clay or ooze in which it was formed. 

 Those from a fine clay usually adhere well together ; those from 

 a globigerina ooze have an areolar appearance ; those from a 

 clay with many fine sandy panicles usually fall to pieces. Mr. 

 Murray attributes the origin of these nodules entirely to the 

 decomposition of volcanic rocks : — 



"Wherever we have pumice containing much magnetite, 

 olivine, augite, or hornblende, and these apparently undergoing 

 decomposition and alteration, or where we have evidence of 

 great showers of volcanic ash, there we find the manganese in 

 greatest abundance. ^ This correspondence between the distribu- 



tion of the manganese and volcanic debris appears to me very 

 significant of the origin of the former. I regard the manganese, 

 as we find it, as one of the secondary products arising from the 

 decomposition of volcanic minerals. 



"Manganese is as frequent as iron in lavas, being usually asso- 

 ciated with it, though in very much smaller amount. In mag- 

 netite and in some varieties of augite and hornblende the protoxide 

 of iron is at times partially replaced by that of manganese. 



" In the manganese of these minerals and in the carbonic acid 

 and oxygen of ocean waters we have the requisite conditions for 

 the decomposition of the minerals, the solution of the manganese, 

 and its subsequent deposition as a peroxide." 1 



These nodules have been examined in the same way as the 

 meteoric dust. Naturally the chief manganese fluting (the chief 

 auroral line) has been seen. 



The question arises, therefore, whether the origin of these 

 deep-sea concretionary deposits of iron and manganese, which are 

 unrepresented in any deep-sea geological deposit, may not be in 

 part, even if in small part, meteoritic, and represent, like the 

 chondroi, another form of fallen dust. 



Proof from Similar Velocities. 



Again, the meteorites, as we have seen, enter our atmosphere 

 with very different velocities. The same thing happens with 

 falling stars, which on this account have been divided into three 

 classes as follows : — 



Class I. Swift, streak-leaving meteors. 

 II. Slow, with trains of sparks. 

 III. Small, quick, short-pathed, sometimes with streaks. 



It has also been determined that the luminous effect which is 

 common to the fall of a meteorite or the appearance of a shooting- 

 star begins at about the same height. In fact, we have in 

 meteorites, large fire-balls, and shooting-star-;, a progression both 

 with regard to the height at which they become visible and the 

 nearness to the earth at which their luminosity is extinguished. 



The actual determination of these heights was commenced by 

 two Gottingen students — Brandes and Benzenberg — in 1798, at 

 the suggestion of Chladni, with the result that the upper reaches 

 of the earth's atmosphere were found to be pierced by bodies 

 entering it with planetary velocities. 



Profs. Herschel and Newton were the first to discuss the 

 data accumulated on this subject, 2 while, as early as 1864, Father 

 Secchi made use of the electric telegraph in securing simultaneous 

 observations. 3 The results of these combined inquiries may be 

 thus shown in the case of shooting-stars : — 



Average 



727 



51-5 



In Herschel's values fire-balls are excluded, and hence the 

 limits are narrower. 4 Fire-balls often arrive within 20 miles 

 of the earth's surface, and then the concussion is of nearly the 

 same intensity whether stones fall or not. 



Such determinations as these, when the observations can be 

 depended upon, can be made with the greatest nicety and by 

 graphical methods. One of the earliest employed — a description 

 of which will give a fair idea of the investigation — is due to 

 Colonel Laussedat. 5 



The observations stating the path of each meteor among the 

 stars having been obtained, a 12-inch celestial globe is "recti- 

 fied " in the usual manner for the place and time. In this way 

 we get first the azimuth and altitude of the beginning and end 

 of each trail. This is done for each place at which the same 

 meteor is observed. 



The results are then plotted on a large-scale map, on'which the 

 altitudes and longitudes of the places of observation and the 

 distances between them can be determined. The scale of the 

 map permits the height of the intersection of the lines of sight to 

 be at once found, and the agreement or disagreement of the obse 

 vations can be noticed, thus allowing the worst observations 

 be rejected. 



1 Murray, Nature, vol. xv. p. 340. 



2 Herschel, B.A. Report, 1863, p. 328 ; Newton, Silliniari s Joxrn 

 2nd series, vol xxxvii., July 1864. 



3 Bull. Meteor., vol. iii. p. 67. 



4 Monthly Notices, vol. xxv. p. 159. 



5 Com/ytes remlus, vol. lviii. p. 1100, 1864. 



