286 British Association for the Advancement of Science. 



those great stumbling blocks of comets, is really superb. How- 

 ever, what I have now to relate, refers to a very singular and in- 

 structive fact in its physical history. I saw the comet for the 

 first time after its perihelion passage, on the night of January 25. 

 Mr. Maclear saw it on the 24th, From this time we of course 

 observed it regularly. Its appearance at first, was that of a round, 

 well-defined disc, having near its center, a very small bright ob- 

 ject exactly like a small comet, and surrounded by a faint nebula. 

 This nebula, in two or three more nights, was absorbed into the 

 disc, and disappeared entirely. Meanwhile the disc itself dilated 

 with extraordinary rapidity, and by measuring its diameter at 

 every favorable opportunity, and laying down the measures by 

 a projected curve, I found the curve to be very nearly a straight 

 line, indicating a uniform rate of increase ; and by tracing back 

 this line to its intersection with its axis, I was led, at the time, to 

 this very singular conclusion, — viz. that on the 21st of January, 

 at 2 h. p. M. the disc must have been a point, — or ought to have 

 no magnitude at all ! In other words, at that precise epoch some 

 very remarkable change in the physical condition of the comet, 

 must have commenced. Well ! all this was speculation. But 

 here comes the matter of fact I refer to, and which, observe, 

 was communicated to me no longer ago than last month by 

 the venerable Olbers, whom I visited in my passage through 

 Bremen, and who was so good as to show me a letter he had just 

 received from M. Boguslawski, Professor of Astronomy at Bres- 

 lau, in which he states, that he had actually procured an observa- 

 tion of that comet on the night of the 21st of January. Well 

 then, how did it appear ? — why, as a star of the sixth magni- 

 tude, — a bright concentrated point, which showed no disc, with 

 a magnifying power of 140 ! And that it actually was the comet, 

 and no star, he satisfied himself, by turning his telescope- on that 

 point where he had seen it. It was gone ! Moreover, he had 

 taken care to secure, by actual observation, the place of the star 

 he observed ; that place agreed to exact precision with his com- 

 putation ; in short, that star loas the comet. Now, I think this 

 observation every way remarkable. First, it is remarkable for 

 the fact, that M. Boguslawski was able to observe it at all on the 

 21st. This could not have been done, had he not been able to 

 direct his telescope point-blank on the spot, by calculation, since 

 it would have been impossible in any other way to have known 



