BUT, to conclude what relates to the _Air_, since the ill Qualities of it in these _Northern_ Countries are not alone sufficient to excite the _Plague_, without imported _Contagion_, this shews the Error of a common Opinion, countenanc'd by Authors of great Name[60], that we are necessarily _visited_ with the _Plague_ once in thirty or forty Years: which is a mere Fancy, without Foundation either in Reason or Experience; and therefore People ought to be delivered from such vain Fears. Since the _Pestilence_ is never originally bred with us, but always brought accidentally from abroad, its coming can have no relation to any certain Period of Time. And although our three or four last _Plagues_ have fallen out nearly at such Intervals, yet that is much too short a Compass of Years to be a Foundation for a general Rule. Accordingly we see that almost fourscore Years have passed over without any Calamity of this kind. THE _Air_ of our Climate is so far from being ever the Original of the true _Plague_, that most probably it never produces those milder infectious Distempers, the _Small-Pox_ and _Measles_. For these Diseases were not heard of in _Europe_ before the _Moors_ had entered _Spain_: and (as I have observed in the _Preface_) they were afterwards propagated and spread through all Nations, chiefly by means of the Wars with the _Saracens_. MOREOVER, we are so far from any Necessity of these periodical Returns of the _Plague_, that, on the contrary, though we have had several Strokes of this kind, yet there are Instances of bad _Contagions_ from abroad being brought over to us, which have proved less malignant here, when our _Northern Air_ has not been disposed to receive such Impressions. THE _Sweating Sickness_, before hinted at, called _Sudor Anglicus_ and _Febris Ephemera Britannica_, because it was commonly thought to have taken its Rise here, was most probably of a foreign Original: and though not the common _Plague_ with _Glandular Tumors_, and _Carbuncles_, yet a real _Pestilence_ from the same Cause, only altered in its Appearance, and abated in its Violence, by the salutary Influence of our Climate. For it preserved an Agreement with the common _Plague_ in many of its _Symptoms_, as _excessive Faintness_ and _Inquietudes_, _inward Burnings_, &c. these _Symptoms_ being no where observed in so intense a Degree as here they are described to have been, except in the true _Plague_: And, what is much more, it was likewise a _contagious_ Disease.