152 NOMOS. 



visible to the naked eye as a star of the second mag- 

 nitude, and with the telescope it presented a well- 

 defined and nearly circular head, surrounded with an 

 exceedingly delicate halo or coma, but without a 

 trace of tail. The bright nucleus was like " a minia- 

 ture comet with a head and tail of its own," and with 

 the tail turned away from the sun. On the 25th and 

 26th the form continued circular, and the only per- 

 ceptible change was in the size. The size, indeed, 

 had become greatly increased, but not uniformly, for 

 the halo had gone on diminishing from the first. 

 On the 28th the halo had ceased to be visible. On 

 the 30th there was a great change both in size and 

 form, the size being greatly increased, and the form 

 no longer circular. On the contrary, the form 

 had now become decidedly parabolic, the outline 

 next the sun being distinct and rounded, and that 

 away from the sun confused and shaded off. From 

 this time up to the 23d of February the comet gained 

 rapidly in size without any material change in form. 

 The addition of new substance, however, was not 

 uniform, and day by day it was evident that the 

 comet gained most in the parts away from the sun, 

 precisely as if it was in the process of recovering its 

 lost tail. As these changes went on, the lustre be- 

 came obscured, and a few days after this time the 

 obscuration became so great that the position of the 

 comet could be no longer recognised. These are the 

 main facts in the history of Halley's comet in the 

 year 1835. 



The comet, then, decreased in size as it approached 

 the sun, and increased in size as it receded from the 



