Observations on the Comet of Halley. 219 



but towards the end it diminished continually. Hooke also, notices 

 particularly the sjDlendor of the nucleus. At this time, the comet 

 did not approach so near the earth, as at its last two visits ; yet it 

 was then much nearer the sun, and this will account for the remark- 

 able splendor of its nucleus. Almost every elementary treatise on 

 astronomy, gives the length of the train in 1682, at 30°, I know 

 not on what authority. The observations of Flamsteed and Heve- 

 lius, shew that such was not the appearance in the north of Europe. 

 In 1607, the comet is described as having a train of considerable 

 length ; yet the accounts do not seem to indicate that it was either 

 then, or in 1531, more splendid than it was in 1835. 



The only other return which can be certainly identified, is that of 

 1456; for although a remarkable comet appeared in 1305, (an in- 

 terval sufficient for about two revolutions of Halley's comet) its iden- 

 tity with the comet of Halley, is not established. Every year a 

 new comet is discovered, and we can only identify a comet on its 

 return to the sun, by means of its elements. These elements can- 

 not be computed for the comet of 1305, for want of accurate obser- 

 vations. At its return in 1456, the comet is described as uncom- 

 monly splendid. Its tail is represented as 60° in length ; and al- 

 though the accounts do not bear the marks of philosophic accuracy, 

 yet it may be true, that it then exhibited a train more splendid than 

 on any subsequent return. Its position was on one account more 

 favorable to its splendor, than it has ever been since that time. 

 The coniet, when it approached nearest the earth, had just passed 

 its perihelion; and this, as is well known, is the time When the 

 train acquires the greatest length. On the whole then, it is by no 

 means settled, that this comet has become sensibly reduced in mat- 

 ter since the time of its first known visit to the sun. That it is more 

 substantial than many known comets is certain ; and it is highly 

 probable that even its long train of 60° bore but a very small pro- 

 portion to the comparatively solid matter of its nucleus. 



Another interesting question here presents itself. Can this com- 

 et be seen at the same distance from the earth and sun after, as be- 

 fore the perihelion passage ? To furnish the means of settling this 

 question, I have computed the following table of relative intensities 



1 



of the comet's light, supposing this intensity to vary as uTTTa' 



where R and D denote the distances from the sun and earth. 



