i860.] 
AMERICAN AGRICULTURIST. 
933 
pressed, and even heaped up at that point, and, as 
■a consequence, it will press the column of mer¬ 
cury higher at that point, while the mercury 
■would sink down at those places where the 
•amount and pressure of the air are lessened by 
the amount drawn off by the wind. The reader 
will here see one reason why the barometer in¬ 
variably falls just before a heavy wind storm— 
the air is drawn away from us by the storm at a 
little distance ; the pressure is less and the ba¬ 
rometer falls. This is an important feature of the 
barometer. It foretells with no little accuracy 
what kind of weather may be looked for. 
The reasons for all the changes in the barom¬ 
eter are not fully understood ; but long continued 
observations have given us several general rules 
for judging of the kind of weather that may be ex¬ 
pected to follow certain indications of the barom¬ 
eter. Each country and district has usually some 
peculiar atmospherical conditions of its own, and 
every possessor of a barometei will soon learn to 
mote its variations, and after a time he will come 
to took to the indications of his instrument with 
-considerable confidence. We give here some 
(GENERAL RULES FOR OBSERVING THE BAROMETER. 
1. After a continuance of dry weather, if the barome¬ 
ter begins to fall slowly and steadily, rain will certainly 
ensue ; but if the fine weather has been of long duration, 
the mercury may fall for two or three days before any 
perceptible change takes place, and the longer the time 
that elapses before the rain comes, the longer the wet 
weather is likely to last. 
2. Conversely, if after a great deal of wet weather, with 
the barometer below its mean hi.ght, the mercury begins 
to rise steadily and slowly, fine weather will come, though 
two or three wet days may first elapse ; and the fine 
weather will be more permanent in proportion to the 
length of time that passes before the perceptible change 
takes place. 
3. On either of the two foregoing suppositions, if the 
change immediately ensues on the motion of the mercu¬ 
ry, the change will not be permanent. 
4. If the barometer rise slowly and steadily for two 
days together or more, fine weather will come, though 
for those two days it may rain incessantly, and the re¬ 
verse ; but if the barometer rise for two days or more 
■during rain, and then on the appearance of fine weath¬ 
er begins to fall again, that fine weather will be very- 
transient, and vice versa. 
5. A sudden fall of the barometer in the Spring or Au¬ 
tumn indicates wind ; in the Summer, during very hot 
weather, a thunder storm may be expected ; in Winter, 
a 6udden fall after frost of some continuance indicates a 
change of wind, with thaw and rain ; but in a continued 
frost, a rise of the mercury indicates approaching snow. 
6. No rapid fluctuations of the barometer are to be in¬ 
terpreted as indicating either dry or wet weather of any 
continuance ; it is only the slow, steady, and continued 
rise or fall that is to be attended to in this respect. 
7. A rise of the mercury late in the Autumn, after a 
long continuance of wet and windy weather, generally 
indicates a change of wind to the northern quarters, and 
the approach of frost. 
Let it be noted, that the above rules do not re¬ 
quire the barometer to stand at any particular 
point to indicate wind or rain ; it is the rising or 
falling of the mercury that is to govern the pre¬ 
dictions as to the weather. A rise or fall from 
29 inches, indicates the same thing as a similar 
rise or fall from 30 inches. Hence the fixed 
marks “rain,” “wind,” “ clear weather,” etc., 
found upon many of the barometers hitherto 
made, are worse than useless—they are decep¬ 
tive, and have done more than any thing else to 
discredit this useful instrument. 
The Boiling Point Barometer. —Thus far we 
have only spoken of the mercurial barometer 
which has been longest in use. There are two 
other modes of determining the pressure of the 
atmosphere. Water usually boils at a heat of 
212°,■ Fahrenheit’s thermometer. At the level 
of the sea the pressure of the air upon the sur¬ 
face prevents its boiling or sending up bubbles of 
steam at a lower temperature. But on mountains, 
there being less air pressing down from above, 
water will boil at a lower temperature. On very 
high mountains, water boils at so low a tempera¬ 
ture that it can not be made hot enough to cook 
potatoes or meats, and roasting or baking has to 
be resorted to. So also the changes in the pres¬ 
sure of the atmosphere are indicated by the tem¬ 
perature at which water boils. We have not 
space to describe the mode of making observa¬ 
tions of this kind, and it is not necessary, as the 
method has more of scientific than practical in¬ 
terest. We will now describe a third method 
which is of great practical utility. 
THE ANEROID BAROMETER.* 
Fig. 5. 
Take any tin box or canister and seal it up 
tightly, removing the air from the inside. At the 
ordinary pressure or weight of the air, the ends of 
the box will be pressed inward somewhat. Now 
let the pressure of the air be a little increased, 
and the ends will be pressed in still further, just 
as the mercury is forced up "in the tube (fig. 4), 
because there is no air inside to resist the exter¬ 
nal pressure. On the contrary, let the pressure 
of the air be lessened, and the ends of the box 
will spring out. Figs. 5 and 6, we have sketched 
to illustrate how such barometers operate. 
In fig. 5, suppose F to be a metallic air-tight 
box or case, with one 
end made of thin brass, 
and a spring inside to 
press it outward with a 
given amount of force. 
If the air be all exhaust¬ 
ed from the interior of F, 
the pressure of the air 
on the outside would 
tend to press the brass end inward against the 
internal spring. Fastened to the brass head is a 
little pivot from which a thread is coiled around 
the shaft, on the upper end of which is an index 
or pointer upon the dial plate. 
Suppose the instrument to be carried up a 
mountain, or from some other cause the atmos¬ 
pheric pressure be comparatively small ; the in¬ 
ternal spring will then throw the brass head out¬ 
ward which will loosen 
the string around the up¬ 
right shaft. The thread 
from the spiral spring S> 
will then turn the index 
back, say to the position 
shown in fig. 5 above. 
Now suppose the instru¬ 
ment be carried down 
to the level of the sea, or that the atmospheric 
pressure be increased from some other cause; 
we shall then have the brass head pressed in¬ 
ward, and the index will then be drawn round to 
a higher figure, say to the position shown in fig. 6. 
It will be seen, then, that the index will be 
moved forward and backward over the dial plate 
from 28 to 31, and thus indicate accurately the 
amount of atmospheric pressure upon the head of 
the box F. With proper adjustment of the box F, 
including the elasticity of the head and of the in¬ 
ternal spring, and also right arrangement of the 
spiral spring S, the strings and shaft, and the in¬ 
dex and dial plate—the index will show the vary¬ 
ing pressure of the atmosphere upon F, just as 
well as does the column of mercury in the upright 
glass tube (fig. 4). [Our engravings, figs. 5, 6, 
are not accurate representations of the internal 
arrangement of any barometer made, but are 
*The name is derived from three Greek words— a, not; 
neros, fluid; and eidos, a form, that is, a-neros-eidos, or 
aneroid., is a form of barometer not having a fluid. 
ideal sketches to illustrate the principle of them 
all Several other parts are usually inserted, 
such as multiplying levers, etc. The vacuum box 
is generally thin, and made of corrugated brass, 
requiring no internal spring to make it elastic. 
In some instruments there is a series of thin 
boxes. Nice adjustments are required to coun¬ 
teract changes of temperature, etc. Our engrav¬ 
ings are only to explain the general operation. 
For very minute scientific investigations prob¬ 
ably a costly mercurial 
barometer is best; but for 
ordinary use a good ane¬ 
roid is preferable, be¬ 
cause it is portable—can 
be carried from place to 
place without danger of 
derangement or spilling 
the mercury. It is also 
small and compact, and 
occupies but little more 
space than a pint cup. 
Kendall’s Aneroid Barometer, (Fig. 7).—At 
the New-Haven Agricultural Lectures last Win : 
ter, Prof. Silliman, of Yale College, called spec¬ 
ial attention to this instrument, and placed it on 
a par with those of European manufacture. We 
sent for one of them during the Spring, and fof 
three months past have frequently compared it 
with one of the best standard mercurial batorrtt?" 
ters kept by Mr. Blunt. It has proved to he ac¬ 
curate beyond expectation. We have recently 
procured several others for friends and sub¬ 
scribers, and they give good satisfaction. We 
present in fig. 7 a sketch of one hanging in out- 
office. The outside brass case is only 4£ inches 
in diameter, and If inches thick. Each one is fitted 
in a neat leather covered box, ahd may be readi¬ 
ly carried to any distance, and requires only to be 
hung up to be ready for use. Everything con¬ 
sidered, these are among the best barometers for 
general use. When required for localities more 
than 4000 feet above the sea level, instruments 
having special adjustments should be ordered, 
for which a small extra charge is made upon the 
usual price. The ordinary price is ten dollars 
Such an instrument is desirable for every fan. 
ily, not only on account of its practical utility L. 
assisting to judge of the weather, but also as 
help towards developing a habit of observation 
on the part of the younger members of the house¬ 
hold. We have placed them among our premi¬ 
ums, and until they are on sale in the country 
generally, we will endeavor to keep a few extra 
instruments on hand for those who can not get 
them conveniently from other sources. 
Night Air. —Many people are afraid of night 
air. Here is what Florence Nightingale says; 
An extraordinary fallacy is the dread of night 
air. What air can we breathe at night but night 
air 1 The choice is between pure night air from 
without and foul night air from within. Most 
people prefer the latter—an unaccountable choice. 
What will they say if it is proved to be true that 
fully one-half of all the diseases we suffer from, 
are occasioned by people sleeping with their 
windows shut ? An open window most nights 
in the year can never hurt any one. In great 
cities night air is often the best and purest air to 
be had in the twenty-four hours. I could better 
understand shutting the windows in towns, dur¬ 
ing the day, than during the night, for the sake of 
the sick. The absence of smoke, the quiet, all 
tend to make night the best time for airing the 
patient. A high medical authority has told mo 
that the air in London is never so 
after ten o’clock at night. 
