128 HISTOEY OP ASTKONOMY. 



disappeared, from increased distance, without any great 

 diminution of length. The comet doubtless had a tail 

 before perihelion, but it seems physically impossible that 

 this should have formed any part of that which was seen 

 after perihelion. The tail was turned nearly toward the 

 earth on the night of February 27th, in such a direction, 

 that had it reached the earth's orbit, it would have passed 

 fifteen millions of miles south of us. Its length was, 

 however, at that time, insufficient to reach any consider- 

 able part of the distance to the earth. 



What gave the comet its extraordinary brilliancy on 

 the 28th of February ? Evidently its proximity to the 

 sun. The day before it had almost grazed the sun's 

 disc. The heat it received, according to the computa- 

 tions of Sir John Herschel, must have been 47,000 times 

 that received by the earth from a vertical sun. The 

 rays of the sun united in the focus of a lens thirty two 

 inches in diameter, and six feet eight inches focal length, 

 have melted carnelian, agate and rock crystal. The heat 

 to which the comet was subjected must have exceeded by 

 twenty-five times that in the focus of such a lens. Such 

 a temperature would have converted into vapor almost 

 every substance on the earth's surface ; and if any thing 

 retained the solid form, it would be in a state of intense 

 ignition. The comet on the 28th of February was red 

 hot and for some days after its perihelion, it retained a 

 peculiar fiery appearance. In the equatorial regions, the 

 tail is described as resembling " a stream of fire from a 

 furnace." The reason why the tail was seen on the 28th, 



