f 212 ] 
fuch obliquity, that the rays from the light fhould 
fall on its furface at an angle of 45 degrees. I then 
fixed a white piper fcreen, at the fame diftance from 
the plate, and under the fame angle with the lan- 
tern, fo that the reflected rays might fall upon it alfo. 
This being done, I obferved, that the reflection from 
the plate diftinCtly was but 17' 30" with an un- 
ventilated hold ; it being turned the colour of tar- 
niflied lead; whereas, when the air was replaced by 
4 hours ventilation, it continued to refleCt light, and 
retain its brightnefs 4 hours 47 minutes. 
3. The fhip’s bell, whofe diameter is 14 inches, 
I had brought into the hold, when ventilation had 
been omitted 12 hours. Having hung it under the 
lower deck, I took out the clapper j and having fuf- 
pended it alfo by thread, which, with its own length, 
made 44 inches ; the angle, which the rim of the 
bell made, with a line let fall perpendicular from the 
pin, on which the clapper hung, was equal to 
34' o". I then held the clapper at the fame angle, 
on the other fide of the line, in order that the flrokes 
at different times might be with the fame force ; 
when, letting it go, it ftruck the bell. In its return 
I catched it, and counting the vibrations, I heard 
them diftinCtly but three times ; wfliereas, when the 
hold was well ventilated, it vibrated five times, j but 
its vibrations were not fo quick in the latter, as in 
the former cafe. I took all poflible precautions, 
that thefe experiments might be fairly tried, to pre- 
vent deception ; but always found them to produce 
the fame effedts. 
We are at prefent very healthy, tho’ our number 
is 130, not one being lick aboard. Our hold, which 
in 
