In answer to this we must in the first place observe, that the accounts of all plagues mentioned in profane history trace their progress from one place to another; whence the probability is, that at its origin the disease was confined to a few, perhaps to a single person. In very few cases, however, has it been possible to trace it to an individual; and, even when this has been done, the unfortunate individual is always said to come from some other place. The instance quoted from Dr. Moore is perhaps the only one upon record where the plague arose spontaneously in any person separated from society; and from a single instance little can be inferred. In those terrible examples we have given of people being burned to death without any accident from terrestrial fuel, the agent seems almost certainly to have been electricity. In the plague of Procopius, said not to have been infectious, the strokes complained of by many patients seem to indicate an action of the same fluid. The same in the plague at London, which was infectious, and likewise of others. But, in cases of plagues which are not infectious, another question arises--By what means do such diseases spread from place to place? for even this dreadful pestilence of Procopius did not overspread the earth at once, but is said to have begun at Pelusium in Egypt. To this no answer can be given. To suppose an omnipresent contagion in the atmosphere, proceeding either from contagion or any thing else, cannot be admitted; for upon this supposition the whole world must have been infected at once. The cause, whatever it was, plainly moved from one place to another, or was successively generated in different places. Recourse may be had to the precipitation of the contagious matter of former plagues from the atmosphere; but to account for this in succession will be found very difficult; and the same difficulty will attend every other solution which may be attempted. Mr. Gibbon indeed censures Procopius for supposing it not to have been infectious; and perhaps the spreading of the disease by infection is the only way by which we can account, in a satisfactory manner, for the way in which it diffused itself over the world, which was, by first infecting the maritime places, and afterwards those which were more inland; always visiting the second year those whom it had spared the first.