CENTURY OF STUDY OF METEORITES. 195 



be plagioclase; and the existence of orthoclase in meteorites has yet 

 to be proved. Continued investigations of the compounds found 

 in meteorites up to the present time have resulted in the detection 

 of at least 21 whose composition is certain, besides several of a 

 somewhat problematic nature. Of these compounds seven have been 

 found to differ in composition from any known terrestrial substances. 

 The character of these indicates the complete absence of water and of 

 ox3'g"en in any large amount from that portion of nature's laboratory 

 where meteorites are formed. Important investigations as to the gases 

 occluded by meteorites were begun by Boussingaidt in 1861 and have 

 been continued by Wright, Ansdell, Dewar, and others. It has been 

 proved that large quantities of hydrogen, as well as carljonic acid gas, 

 are contained in these bodies, under pressure greater than that of 

 the earth's atmosphere. These investigations led further to the spec- 

 troscopic study of meteorites by Vogel, Wright, and Lockyer. The 

 spectra thus obtained, when compared with those exhibited by comets, 

 showed striking resemblances, which have led to a growing belief 

 among scientific men in the identity of origin of comets and meteorites. 

 Lockyer has indeed pushed this conclusion to the point of believing 

 that "'all self-luminous bodies in the celestial spaces are composed either 

 of swarms of meteorites or of masses of meteoric vapor produced by 

 heat,-' and he draws from this m;iny important deductions relating to 

 the origin of the stars, comets and nebuUc, and the physical condi- 

 tions prevailing in them. It will remain for the twentieth century to 

 test the correctness of such conclusions, but the facts already lirought 

 out have considerably shaken the confidence hitherto placed in the 

 nebular hypothesis. Another interesting result of the century has 

 been the establishment of a general similai-ity between shooting stars 

 and meteorites. This idea was first suggested by Chladni in 1798, 

 but it has remained for Newton, Adams, and Schiaparelli to give it 

 shape and proof. The general verdict of science is now in accord 

 with the belief of Newton, "that from the faintest shooting star to the 

 largest stone meteor wii pass l)y such small gradations that no clear 

 (li\iding lines can separate them into classes." Moreover, the long- 

 existing belief in le vide ])lanetaire, space filled only with a mysterious 

 fiuid called ether, has been shown to l)e luitenable. Careful records and 

 estimates have shown that 20,000,000 cosmic l)odies large enough to 

 produce the phenomena of shooting stars are encountered b}' the earth 

 daily. The number of these bodies existing in space must be, therefore, 

 beyond all calculation, and their existence implies that of smaller par- 

 ticles in sufficient nuni])er to form a widely pervasive cosmic dust. 

 Man}^ remarkable meteorite falls have occurred during the century. 

 Begitming with the stone shower of L'Aigle in 1803, when 2,000 to 

 3,000 stones fell, no less than eleven such showers have Ijeen recorded. 

 In the shower of Pultusk, Poland, which occurred in 1868, 100,000 



