the limits of an aiinosphcre of mercury (tliat is, the clcvatiou 

 at which mercurial vapors precipitated" ou gold leaf cease 

 perceptibly to rise in au air-lilled space) have given consid- 

 erable weight to the assumption of a definite surface of the 

 atmosphere " similar to the surface of the sea." Can any 

 gaseous particles belonging to the region of space blend with 

 our atmosphere and produce meteorological changes ? New- 

 ton* inclined to the idea that such might be the case. If 

 we regard falling stars and meteoric stones as planetary as- 

 teroids, Ave may be allowed to conjecture that in the streams 

 of the so-called November phenomena,! when, as in 1799, 

 1633, and 1S34, myriads of falling stars traversed the vault 

 of heaven, and northern lights were simultaneously observed, 

 our atmosphere may have received from the regions of space 

 some elements foreign to it, which were capable of exciting 

 electro-magnetic processes. 



II. 



NATURAL AND TELESCOPIC VISION.— SCINTILLATION OF THE STARS 

 —VELOCITY OF LIGHT.— RESULTS OF PHOTOMETRY. 



The increased poAver of vision yielded nearly two hundred 

 and fifty years ago by the invention of the telescope, has af- 

 forded to the eye, as the organ of sensuous cosmical contem- 

 plation, the noblest of all aids toward a knowledge of the 

 contents of space, and the investigation of the configuration, 

 physical character, and masses of the planets and their sat- 

 ellites. The first telescope was constructed in 1608, seven 

 years after the death of the great observer, Tycho Brahe. 

 Its earliest fruits Avere the successive discovery of the satel- 

 lites of Jupiter, the Sun's spots, the crescent shape of Venus, 

 the ring of Saturn as a triple planetary formation (planeta 

 tergeminus), telescopic stellar swarms, and the nebulae in 

 Andromeda. $ In 1634, the French astronomer Morin, emi- 

 nent for his observations on longitude, first conceiA'cd the idea 

 of mounting a telescope on the index bar of an instrument 

 of measurement, and seeking to discover Arcturus by day.§ 



* Newtou, Princ. Matkem., t. iii. (1760), p. 671: "Vapores qui ex 

 sole et stellis fixis et caudis cometarum oriuiitur, incidere possvnt in at- 

 mospbteras plauetarum " + Cosmos, vol. i., p. 124-13.5 



X See Cosmos, vol. ii., p. 317-335, with notes. 



$ Delainbre, Histoire dc f Astronomie Moderne, torn, ii., p. 2.55, 269 



