An essay on comets [microform] : in two parts : part I, containing an attempt to explain the phænomena of the tails of comets, and to account for their perpetual opposition to the sun, upon philosophical principles : part II, pointing out some important ends for which these tails were probably designed : wherein it is shewn, that, in consequence of these curious appendages, comets may be inhabited worlds, and even comfortable habitations : notwithstanding the vast excentricities of their orbits : the whole interspersed with observations and reflections on the sun and primary planets / by Andrew Oliver