3^6 Dr. ingenhousz on the Salubrity 
find in it. I began my experiments at Gravefend, where 
I was obliged to wait two days for a favourable wind. I 
found the air of that place, on Nov. r, of a tolerable 
good quality, as one meafure of it with one of nitrous 
air occupied, in feveral trials', about 104, or one meafure 
and of a meafure ; fo that I took it to be nearly of the 
fame quality as the air of London. 
The fhip in which I went from London to Oftend 
happened to be becalmed about two or three miles from 
Ihore, in the mouth of the Thames, between Sheernefs 
and Margate. The weather was very agreeable, warm, 
and the fun fhone very bright, on the 3d of November. 
I was provided with a travelling apparatus, made on pur- 
pofe by Mr. martin, the whole of which was packed up 
an a box about ten inches long, five broad, and three and 
an half high. The glafs tube or great meafure, which was 
fixteen inches long, and divided in two feparate pieces, 
lay in a frnall compafs, and could be put together by 
brafs fcrews adapted to the divided extremities. Inftead 
of a water trough, fuch as is ufed commonly, I made ufe 
of a frnall round wooden tub, which I found on board 
the ihip, and which I filled with fea-water, fixing to the 
edge of this tub, by means of a fcrew, the brafs funnel, 
through which the air was to be let up into the glafs 
tube. 
After 
