Sir, As you had recommended to me the examination of the air at sea by the nitrous test, I followed your advice in my return to the Continent in the beginning of November last: and I embraced that opportunity with the more eagerness, as I knew that you had given credit to the account of several consumptive people having recovered their health by going on sea voyages, after the common means for curing that distemper had failed. I was in hopes likewise to find in this inquiry, a confirmation of what you conjectured in you Anniversary Discourse in the year 1773,
viz
. that great bodies of water, such as seas and lakes, are conducive to the health of animals, by purifying and cleansing the air contaminated by their breathing in it: so that the salutary gales, by which this infected air is conveyed to the waters, and by them returned again to the land, though they do rise now and then to storms and hurricanes, must nevertheless induce us to trace and to reverse in them the ways of a beneficent Being, who, not fortuitously, but with design, not in wrath, but in mercy, thus shakes the waters and the air together, to bury in the deep those pestilential effluvia which the vegetables upon the face of the earth are insufficient to consume.
XXIII. On the degree of salubrity of the common air at sea, compared with that of the sea-shore, and that of places far removed from the sea