562 COSMOS. 



which the zodiacal light radiates from a vapoury, flattened 

 ring, freely revolving in space between the orbits of Venus 

 and Mars, appears in the very deficient state of observation 

 to be the most satisfactory. The outermost limits of the 

 Sun's atmosphere, like that of Saturn (a subordinate system), 

 could only extend to that point where the attraction of the 

 universal or partial central body exactly balanced the centri- 

 fugal force ; beyond this point the atmosphere must escape at 

 a tangent, and continue its course either aggregated into 

 spherical planets and satellites, or, when not aggregated into 

 spheres, as solid and vaporous rings. From this point of view 

 the ring of tlie zodiacal light comes within the category of 

 planetary forms, which are subject to the universal laws of 

 formation. 



From the small progress which this neglected part of our 

 astronomical knowledge makes on the path of observation, 

 I have little to add to that which I derived from the expe- 

 rience of others and myself, and have previously developed 

 in the Delineation of Nature (vol. i. pp. 127-134 ; vol. iv. 

 p. 308). If, 22 years before Dominique Cassini, to whom 

 the first detection of the zodiacal light is erroneously as- 

 cribed, Childrey, the chaplain of Lord Henry Somerset, had 

 already recommended this phenomenon to the attention of 

 astronomers in his Britannica Baconica, published in 1661, as 

 one which had previously been unnoticed and observed by him 

 during several years, in February and the commencement of 

 March ; so must I also mention (according to a remark of 

 Olbers) a letter which Rothman wrote to Tycho, from whence 

 it results that Tycho saw the zodiacal light as early as the end 

 of the sixteenth century, and considered it to be an abnormal 

 spring-evening twilight. The strikingly greater luminous 

 intensity of this phenomenon in Spain, upon the coasts of 

 Valencia and the plains of New Castile, first incited me to 

 continuous observation before I left Europe. The strength of 



