DR. _Plot_[20] tells us, That about Twenty Years since, two Persons were employed to dig a Well in the Parish of _North-Leigh_ in _Oxfordshire_, but upon being taken ill, left off the Work: Whereupon it was undertaken by two others of _Woodstock_; who, before they could do any thing considerable in it, sunk down, and died irrecoverably in the Well: Which being perceived by a Miller hard by, and he coming to their Assistance, fell down dead upon them. Another also venturing to do the same, with a Rope tied about him, fell from the Ladder just in the same Manner; and though presently drawn up by the People above, yet he was scarcely recover’d in an Hour or more. And since then, upon a Bucket’s falling into a Well in another Part of the Town, a Woman perswaded a strong lusty Man to go down a Ladder to fetch it, who, by that Time he had got half way down, fell from the Ladder into the Well; upon which, the Woman called another of her Neighbours to his Assistance, who, much about the same Place, met with the same Fate, without giving the least Sign of Change; so fatal (says the Doctor) are the Damps of that Place. Dr. _Boot_[21] tells a Story that happened at _Dublin_ in _Ireland_, just of the same Nature. And in the _Philosophical Transactions_[22], there are the like Relations of Damps in the Coal-Mines belonging to the Lord _Sinclair_ in _Scotland_. THE most surprizing Effect of these subterraneous _Effluvia_ that I ever met with, is in a Relation of Dr. _Bernard Connor_, of certain Persons in _Paris_ digging deep in a Vault or Cellar, who were so suddenly transfixed by some subtile Vapour, that when a Servant-Maid came down to speak with them, she found them in Postures as if at Work; one with his Pick-Ax advanced, another with his Shovel full of Earth, half lifted up, and a Woman sitting by with her Arm upon her Knee, her Head leaning upon that Hand, with manifest Expectations in her Countenance of what they were in Search after. THE same Author, from his own Knowledge, gives a very exact Account of a _Grotta_ in _Italy_, much talked of, and commonly called _la Grotta de cani_, by this Author, _Crypta_ Κυνιχυς; But Dr. _Mead_ hath since, from his own Knowledge also, given a very particular and rational Account of this Place, and the Manner of its killing; to whom therefore the Reader may turn for further Satisfaction. ANOTHER, and more general Cause than any hitherto mentioned of these Maladies, is some bad and unwholsome Constitution of Air. Such Constitutions may arise from several Causes, which although they affect us in different Manners, yet as they are equally fatal, we call them all _Malignant_ or _Pestilential_: In Order therefore to understand the better how we are differently affected by those different Constitutions, it will be proper to consider them somewhat distinctly, under these general Heads, _viz._ _A dry hot Air_, _hot and moist_, _cold and moist_, _and cold and dry_; to which most Variations of Air may be reduced.