386 Mr. Harvey on the effects of the density of air 
where the average density is sensibly diminished. In a 
subsequent part of the paper it will also appear, that the 
uncertain fluctuations of the barometer at the level of the 
sea, produces in many cases minute, but sensible changes of 
rate. 
2. The effects recorded in the preceding section of the 
paper having been produced by a diminution of atmospheric 
pressure, it was conceived, that results entirely the reverse 
would arise from an increase thereof ; that is, if a chrono- 
meter gained by being placed in air of a less density than 
that afforded by the ordinary state of the atmosphere, it 
ought to lose, by being subjected to air of a greater. Accord- 
ingly, by introducing different time-keepers into a condensing 
engine, furnished with an appropriate mercurial guage, the 
opposite results here alluded to actually took place. 
Not knowing the effects likely to be produced on so deli- 
cate a machine as a chronometer, by placing it in air con- 
densed to any considerable degree, the time-keeper H, 
employed in the former investigations, was first placed in 
air of a density corresponding to 34 inches of mercury. The 5 
result was an alteration of the mean detached rate of the 
chronometer from + 6 ". 9 to -f- 5". 3. The chronometer was 
♦ 
necessarily removed from the condensing machine for a few 
minutes each day, for the purpose of comparison, and being 
wound up. 
On restoring the time-keeper to the ordinary pressure of 
the atmosphere, its rate returned to -f- 6". 5, agreeing within 
o".4 of its former detached rate. In a second experiment, it 
was subjected to air denoted in density by 38 inches of quick- 
silver, when its rate altered from -f 6." 5 to s". 3 ; and on 
