110 A Calcidatiori of the Orbit of the Comet. 



except that of 75 yeafs, whose returns appear to have 

 been observed by astronomers, several times in succes- 

 sion ; yet admitting those of 1532 and 1661 to be one 

 and the same comet, it is evident, that its periodical 

 time must have varied from that of its preceding revo- 

 lution ; and if this be the case, it furnishes another fact 

 illustrative of the theory which I have advanced. 



Dr. Halley, in his cometography, prompted, undoubt- 

 edly, by that enthusiasm which he felt for scientific im- 

 provement, says, that " time will reveal to posterity all 

 the mysteries of comets," or in words to this eifect. But 

 when the causes, which retai'd the progress of this branch 

 of science, are duly considered, few will hesitate to adopt 

 the contrary opinion, that ages will pass away before 

 mankind can attain to much more knowledge of the co- 

 mets, and that the periods of many will ever remain a 

 problem, above human research nnd investigation. 



Cmchmati, Jan. 24, 1808. 



