Astronomy and Meteorology. 293 



by the great comet of 1 858. It is divided into XV sections. Section I 

 contains llie details of observations upon the figure, dimensions and posi- 

 tion of the tf.il. The whole period of visibility of the comet extended from 

 June 2, 1858, to March 4, 1859, an interval of 275 days. It was seen 

 J>th the naked eye from Aug. 19 to Dec. 9, an interval of 112 days, 

 ilie tail appeared first on Aug. 14, 1858, and was iu sight until Feb. 9, 



Section II comprises observations 

 consisted chiefly of long, narrow an 

 quite faint, and escaped general notice. 



Section III gives the details of the reduction of the observations upon 

 tne figure and position of the tail. The maximum length of the tail was 

 64° on the 10th of October; the greatest breadth was 18° on the day 

 following._ 



Jn Section IV are considered the probable errors affecting the observa- 



Section V describes the deflection of the upper part of the tail. 



Section VI describes the columnar structure, or the division of the 

 iipper part of the tail into alternating dark and bright bands, disposed 

 transversely to the axis, at angles of 20° or 30°. 



Section VII contains the reduction of observations on the secondary 

 tails. The principal ray attained a length of 55°. 



The original data relating to the envelopes and nucleus, and to the 

 phenomena of the head of the comet generally, are comprised in Section 

 ^ill. The citations are made from 71 authorities, representing 51 



The first traces of a peculiarity in the nebulosity near the nucleus, 

 ^liich led finally to the full development of the envelopes, were men- 

 tioned on Sept. 11th. The light was seen streaming outward from the 

 ^"cleus, on the side nearest the sun, bending backward to form the two 

 branches of the tail. 



Section IX treats of the outline of the head of the comet. The dis- 

 ^ssion is based upon 123 outlines, derived from the original drawings 

 or engraved figures. It appears that the limiting surface of the head of 

 we comet had a close resemblance to a surface generated by the revolu- 

 tion of a catenary on its vertical axis. 



A"e phenomena of the branching and central darkness of the tail have 

 *>een considered in Section X. On the 24th of August, the right branch 

 f'ready showed an excess of light, and the contrast in density went on 

 increasing until it reached a maximum about the time of the perihelion 

 passage. 



The size of the nucleus, and the quantity of light emitted by it and by 

 tiie head generally, form the subject of Section XL The diameter of the 

 '^tuf 1 solid nucleus must have been less than 500 miles. On the 2nd 

 of October, the brightness of the head of the comet was 6300 times 

 heater than on June 15th, the increase by observation exceeding that 

 ^niputed by the usual formula, by 33 times. The difference is referred 

 ^ an increase in the aggregate reflecting surface of the comet. 



The phenomena presented by the envelopes are considered in Section 

 ■^ One of the most important of these is their regular succession, and 



