406 ANNUAL OF SCIENTIFIC DISCOVERY. 



First The substance giving the zodiacal light formed a complete circle 

 round the earth, as at all the observations which had been taken it was found 

 that the light extended completely across the sky from cast to west ; and 

 from the observations having been taken at regular intervals during the 

 night, the arch was observed at different angles to within eighteen degrees of 

 a complete circle. 



Second It was a great circle, forming an angle of three deg. twenty 

 min. with the ecliptic, the ascending node being at longitude sixty-two deg., 

 and descending node at longitude two hundred and forty-two deg. The 

 width appeared to vary at different times, seeming to be greatest at the latest 

 observations, which he attributed to his sight having become more accus- 

 tomed to the light. He came, however, to the conclusion that the average 

 width as seen with the eye is twenty-eight degrees, which, at say 100,000 

 miles, would give a nebulous circle of enormous extent. 



Third It is a geocentric circle. If it were heliocentric, then the portions 

 in the direction of the sun would have to be 170 or 190 millions of miles 

 from the spectator, and the opposite side comparatively near to him, conse- 

 quently this ring, by the rules of perspective, would be made at the nearest 

 part, and greatly narrowed near the sun, where it would terminate almost in 

 a point. 



The facts are not so, for the ring has the same width in its whole extent. 

 Again, if heliocentric, the laws of optics for reflected light would require the 

 portion nearest to a line with the sun to give less reflected light than 

 towards the spectator's zenith ; but the fact is that the light nearest the hori- 

 zon is always much brighter than it is higher up. Again, the brightest por- 

 tion of the zodiacal light showed an affinity to the spectator's motion as his 

 zenith approached or receded from the ring, which can belong only to an ob- 

 ject not very far off. 



ON THE DISTRIBUTION OF THE ORBITS OF COMETS. 



The following is a resume of a paper read before the British Association 

 at is last meeting, by Prof. M. Mosetti, on the above subject : 



The author commenced by explaining that the simplest and most direct 

 method of analyzing the distribution of the comets in space would seem to 

 be, to divide the celestial sphere by means of circles parallel to the ecliptic 

 into equal zones corresponding to an aliquot part of the entire superficies, 

 and then to ascertain how many culminating points arc contained in each of 

 these. If the orbits were uniformly distributed throughout space, each of 

 them should contain about an equal number of these points ; if not, the greater 

 or less number contained in each Avill serve to show the tendency the orbits 

 have to approach to or recede from that distribution. The author applied 

 this method arithmetically in the first instance ; and afterwards, in order to 

 render the results more palpable, reduced them to a graphic construction. 

 He thus found the orbits to have a tendency to approach in prevailing 

 numbers the polar regions of the ecliptic. The minimum occurs in the fifth 

 zone of each hemisphere. , Those whose parhelia are in the Northern hemis- 



