1854.] OF THE ROYAL INSTITUTION. 427 
saturated solution of muriate of soda seemed at first more suc- 
cessful, but in a short time the column became depressed, and this 
depression continuing to increase at a regular rate, the tube was 
emptied, when it was found that the salt having crystallized be- 
tween the mercury and the glass, had so allowed the air to enter. 
A solution of muriate of lime, not being crystallizable, was 
next tried; and this seems to stand best, as yet having sunk in 
21 years only ‘03 of an inch, the greater part of this depression 
having occurred in the first few months, giving rise to the surmise 
that the air which has caused it was left in at the time of filling, 
and has not crept in since. ‘The addition of the salt to the water, 
besides removing to a great extent the air, has the effect of 
diminishing the correction required for the force of vapour; the 
last named solution has its boiling-point at 234° F., and, as has 
been shown by experiments, the tension of vapour from water 
and watery solutions of salts is the same at an equal number of 
degrees below their boiling-points, the correction to be applied is 
lessened to that of pure water 22° lower than the observed tem- 
perature. This correction, which is to be added, and that for the 
expansion of the fluids, which is to be subtracted, thus nearly 
neutralizing each other at low temperatures, I have applied by 
means of a moveable scale, in the same way as is used in the 
sympiesometer. Among the slighter variations shown by this 
barometer may be mentioned the oscillations during a gale of wind ; 
these are quite as conspicuous in this barometer as they were 
observed by Professor Daniell in the water barometer, amounting 
frequently to 0°03, and once to 0°04 of an inch; they vary in 
duration from 5 to 7 seconds; they begin with a short, quick 
rise, followed by a slower and much greater descent, and then a 
return to the point of rest, which is much nearer the top than the 
bottom of the oscillation. Previously to a gale of wind, the 
column descends by jerks and with irregular rapidity ; but on one 
occasion, on which no wind followed for two days, the column 
fell without the slightest jerk more than half an inch ; there was, 
however, a heavy and long-continued fall of rain. During heavy 
and sudden showers the column rises, and falls again on the cessae 
tion of the shower ; on one occasion the rise was ‘02 of an inch. 
In a room with a fire, with a door and window shut, the column 
is lower than when the window is open; the difference is usually 
“005, but with a good fire ‘Ol of an inch. The last two causes 
are very likely to give rise to error, and the better the barometer 
the greater will be the error, 
[W. R.] 
