662 KANSAS CITY REVIEW OF SCIENCE. 



the same orbits continuall}'. They appear to the people of the earth at stated 

 periods ; some have longer periods than others. Encke's comet has the shortest 

 period, viz.: three and one-half years, while some comets have periods as long as 

 thirty-three, forty and even seventy-five years. A view of the great comet of 

 1811 was shown on the screen. That was the largest comet ever known. The 

 diameter of the head was not less than the diameter of the Sun. That comet 

 never came within 100,000,000 miles of the earth, and yet it was a remarkable 

 sight. Its tail was 60,000,000 or 70,000,000 miles in length. Prof. Young said 

 that he had seen comets more than 50,000 miles in diameter running centrally 

 over stars without dimming the stars in the slightest degree. It had been esti- 

 mated that the mass of a large comet was equal to a lump of iron 100 miles in 

 diameter, but the lecturer was inclined to doubt the correctness of that estimate. 

 It had been clearly demonstrated that astronomical observers could see through 

 the thickest part of a comet. Several views were exhibited to give the audience 

 an idea of the different shapes and phases of comets. Biela's comet divided into 

 two parts in 1842. The parts separated and gradually disappeared from view, 

 and Prof. Young said that all that remained of them now was a shower of falling 

 stars. The present comet was illustrated by various diagrams. One of the most 

 remarkable things about this comet is the nearness of its approach to the Sun. 

 It apparently almost scraped the solar surface. Moving at times with a velocity 

 of 300 miles per second it had gone from one side of the Sun to the other inside 

 of three hours. The comet of 1843 was very like the present comet. Its tail 

 was about 100,000,000 miles in length, but it, too, succeeded in going from one 

 side of the Sun to the other in three hours. The "whiskiness" of the tail of 

 the comet of 1843 had caused much comment and discussion among astronomers. 

 It was a matter of wonderment that a tail of so great length should be able to 

 encircle the Sun in so short a time. Various different theories had been advanced 

 on this point. 



The office of comets in the planetary system is not known. Much has been 

 written on the subject and many opinions have been advanced, but nobody can 

 feel that a correct explanation of the use of these remarkably brilliant bodies has 

 been given. It was suggested by Sir Isaac Newton that comets supplied the 

 material for the preservation of light. Prof. Young did not know but that such 

 might be the^fact. It was an established fact that carbonic acid was an essential 

 element of the atmosphere, and it was known that that element was disappear- 

 ing. Who knows but that the comets are destined to supply the subtle influence 

 needed to preserve the light with which the people of this globe are favored ? 

 The lecturer stated that he had received a letter which, he judged from the hand- 

 writing, must have come from a lady, asking whether there were inhabitants on 

 the planets other than the earth. In reply, he desired to say that in point of 

 actual fact the inquirer knew as much about the matter as he did. The only 

 known planets that could possibly be inhabited by people such as dwelt on the 

 earth were our nearest neighbors, Venus and Mars. It was possible that there 

 were people, used to tropical climates on this planet, who could live on Venus. 



