?68 



Marvels of the Universe 



some manitestation of an electric nature may be involved. To this it maj' be added thar some 

 recent Comets, especially Morehouse's of 190S, have exhibited transformations in their tails of a 

 kind not generalh" noticed or recognized in the past. These transformations have included a 

 development of swellings in the tail not unlike knots in a rope ; whilst in a somewhat larger 

 number of cases it has been noticed that a Comet has, as it were, shed portions of its tail, which 

 have fallen off and become distinct fragments. Even beyond this there are a few cases on record, 

 such as that of Biela's Comet, where Comets have broken up, have become disintegrated and 

 scattered throu.gh space to form the objects which we call lummous meteors. 



As regards their motions, some Comets are very regular and others verj' erratic. The Comets 

 which are regular in their movements are technicall}' termed " periodic Comets," and circulate 



Pholoi III'] [I'rof. E. E. llarnard. 



MOREHOUSE'S COMET OF 1908. 



These two photographs exhibit remarkable developments in the tail of this Comet which had not been generally noticed 

 previously. These changes have included the formation of swellings in the tail not unlike knots in a rope, as shown in the 

 second photo. 



round the sun in regular or closed orbits. The erratic Comets come up to the sun and become 

 visible to us, having tra\'elled from whence we know not. and pass on after they leave us, whither 

 we know not. 



The periodic Comets may be grouped in two classes. The first class includes those Comets which 

 visit us with great regularity at stated intervals of from three to a dozen years, or thereabouts ; 

 whilst there is also a small group which seem to belong to our system, and may be expected to 

 reappear about every seventy years. Of these the well-known Comet of Halley is a noteworthy 

 example. The second class, which we verily believe are really periodic, judging bv the calculated 

 form of their orbits, have periods supposed to amount to many hundreds of years. Therefore, they 

 have not proved to us yet their periodicity by paying us a second visit, though they may do so 

 perhaps some centuries hence, if the world lasts so long. 



Something should be said about the numbers of the Comets. The total number recorded from 



