THE MOON, PLANETS, AND COMETS 263 



thus predicted its return and described the circumstances 

 of its appearance. Most people laughed at this ; but as the 

 time drew near, scientific men who knew the soundness of 

 the principles on which the prediction was based became im- 

 mensely interested hi the question of the return of the comet. 

 Halley's prediction was verified, for not only did the comet 

 return, but twice since it has passed near the sun and become 

 visible from the earth the last time in 1910. Its next 

 appearance will be in 1986. When it was near the earth, 

 its head appeared to be nearly as large as the moon and its 

 tail stretched one third the distance across the sky. In spite 

 of these great dimensions it was not very conspicuous. Other 

 comets have been seen which were so bright that they were 

 visible even in the daytime. 



The superstitions regarding the evil influences of comets 

 have been dissipated by the advance of science, but many 

 people still fear that if a comet should actually strike the 

 earth, all life on the earth might be destroyed. The result, 

 of course, depends primarily upon the mass of comets, about 

 which nothing is certainly known. If the earth should pass 

 through the tail of a comet as has happened a number of 

 times in the last century no harm would be done. Even 

 if the earth should collide with the head of a comet, it is 

 not probable that there would be serious injury to the earth 

 or the people who live upon it. 



