Meteoric Shoiver of 1S36. 393 



Stretching across the earth's orbit obliquely, so that the earth passes un- 

 der it in its annual progress, while places on its surface lying westward 

 of each other are successively brought by the diurnal revolution to the 

 point of nearest approach, will satisfy both these conditions. I can 

 think of no other that will. The " point of nearest approach" may be 

 merely the extremity, or the skirt of the nebulous body, while the 

 greatest part of it, and consequently its centre of gravity, lies too 

 distant from the earth to be much influenced by its gravity. It would 

 not be at all inconsistent with the known extent of astronomical bodies, 

 to give to the body in question a breadth of thousar>ds, and a length 

 of millions of miles. 



It was an accidental observation, made after the conclusion was form- 

 ed, which ascribes the origin of the meteoric showers to a revolving 

 nebulous body, that first led me to suspect the Zodiacal Light to be 

 the body in question. This, according to La Place, is such a nebu- 

 lous body, revolving around the sun in the plane of the solar equator.* 

 We actually observe it to reach over the orbit of the earth, making 

 an angle with its plane of only 7:| degrees. It is not difficult to 

 place it in such a situation that the earth shall come very near to the 

 shirts of it at least. We should, indeed, expect this meeting of the 

 two bodies to take place at the nodes of the solar equator, and there- 

 fore in December and June instead of November and April. It is 

 easily conceivable, however, that the aphelion of the Zodiacal Light, 

 at which place it approaches nearest to the earth, does not lie exactly 

 at the node, but so far from it that the earth passes it a month before 

 it comes to its node, at which time, moreover, the earth is more than 

 a million of miles nearer to the sun than its mean distance. In en- 

 deavoring to fix the periodic time of the meteoric body, since it must 

 be either a year or half a year, (for no other periodic times could 

 bring the tvi^o bodies together at intervals of a year,f ) several con- 

 siderations induced the belief, that half a year was the true period — ■ 

 an inference drawn especially from the apparent great excess of ve- 

 locity of the earth at the point of concourse ; but the period of a 

 year, (or more probably, a little less than a year,) by implying that 

 the two bodies are always comparatively near to each other, would 

 better explain the occurrence of shooting stars at all seasons of the 

 year, and would be particularly favorable to the explanation of those 



* Mec. Celeste, (Bowditch,) Vol. II. 525. 

 + See Vol. XXVI. p. 166, of this Journal. 

 Vol. XXXI.— No. 2. 50 



