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few facts which will serve to show that the barometer is a very useful instrument. In the first place, it indicates the future state of the weather; for that reason alone, no family should be without one, particularly the farmer, for he would be enabled to follow his business in the field with greater success. barometer is also extremely useful in measuring heights. The cause which produces the result in this connection, is the effect, from the elasticity of the atmosphere, which diminishes as the aerial space enlarges. Thus, the suspension of the mercury in the tube is due to the atmospheric pressure; when it is carried to a place above the sea, its column becomes shorter. This is proven by the result of actual experiment, which led me to the arrangement of a very easy rule by which even the traveler on the cars can now, by means of the barometer, determine with great facility, and a considerable degree of accuracy, the height of any place whatever, above the sea.

Again the oscillations of the barometer have taught us that the mean pressure of the atmosphere at the level of the sea is equal to about 14 pounds on the square inch. This same pressure is also equal in weight to a column of mercury one inch square and thirty inches high. And again, by these means, we are enabled to ascertain the pressure of the whole mass of the atmospheric air with almost as much precision as if we actually weighed it.

By means of long-continued observations of the barometric changes which are due to the atmospheric conditions, I have been enabled to deduce the following general results, which will be found new and of great practical interest, for such will not only serve to remove frequent misconceptions in consulting the instrument, but the observer can with greater convenience form his opinion of the future state of the weather, and also determine the height of his locality from the level of the

ocean.

Before consulting a barometer, it should be remembered that the range of its mercurial column is greater in winter than in summer, and that, by the average pressure of the atmosphere at the surface of the ocean, there the mean height of the mercury, at a mean temperature of 32 degrees, stands at 30 inches. But when on the continent, where its mean be found one-tenth below 30 inches, indicates an elevation 86.85 feet above the sea.

From these facts it will be seen that the changes of weather are not indicated by the actual height of its mercury to the words "fair, change, etc." generally marked on the plate.

The indications can only be determined by its variation of height and the manner in which that variation takes place. Therefore the observer of a barometer is desired to devote his attention to the following notes:

1. Set the barometer in the morning, and when the mercury rises one-tenth

above its normal position, indicates

2. A depression of .05 inch from that point indicates

3 A depression of .08 indicates (in about twenty-four hours)

Fair. Change. Rain.

Stormy.

4. A sudden and considerable depression indicates

5. A very sudden and considerable depression, at the rate of one-tenth inch an hour, indicates

6. An indication of rain, the rain not falling, indicates

7. If no indication of rain, and rain should fall, indicates

Hurricane. Dry Weather.

Wet Weather.

8. A sudden and rapid rise of the mercury is an indication of a fresh and strong N. W. wind; and a clear sky will follow.

The annual mean of the barometer (with the thermometer attached) can be ascertained by registering their daily heights at noon; and then, after one year's observation, add up those daily heights, and divide the product by the number of observations. The quotient will express the annual mean.

THE ANEROID BAROMETER.

Experience has shown that the column falls before the approach of a storm, and rises before fair weather. Hence this instrument is of great value to the sailor upon the ocean; and few or no ships sail without being provided with one. It is also of exceeding value to the farmer, especially in haying and harvesting time. Some have objected to the mercurial barometer for farmers' use. One of these objections is its cost, growing out of the great care necessary in its manufacture, to render it perfect, in depriving the column of every particle of air, which is done by boiling the mercury in the tube, and by other means involving considerable labor and expense. These instruments are sold as low as seven to ten dollars, but reliable standard instruments sell for a much higher price. Other objections are its liability to break and to get out of order.

Recently another form of the instrument has been invented, which in many respects is much preferable, and is known as the "aneroid barometer." The name is significant of the formation of a vacuum without a fluid; and the form of this barometer is greatly in contrast with the Torricellian tube. The principle on which this instrument operates seems to have been first noticed by M. Conte, a French professor, but was finally reduced by M. Vidi. At the New Haven agricultural lectures, in February last, Prof. Silliman, Jr., devoted an hour or two to the subject of meteorology, in which he described the various forms of this instrument. Of the aneroid barometer, which he deemed the most important instrument that could be placed in the hands of the farmer, he said: "Unqualifiedly, it is the best for the farmers' use; and for the scientific man, its portability, and almost total unliability to accident, strongly recommend it. The old mercurial barometer, with its marks of 'cloudy,' rain,' fair weather,' etc., is utterly unreliable; for the pressure of the atmosphere at divers heights is different; and the pressure that near New York rises to fair weather,' would at a higher place, say the prairies, stand at foul' And then, again, if roughly handled, air will leak into the instrument, and its value be utterly destroyed. The aneroid barometer (or the 'without fluid' barometer) was first invented by M. Conte, a professor at the Erostatical School at Meudon, near Paris; but an American mechanic

has made it much cheaper, and as equally reliable as the expensive French Instrument." He sells it for the moderate price of $7 50-only one-third the cost of a Smithsonian barometer.

The aneroid consists of a flat and circular metallic box, the cover of which is very thin and corrugated, or in ridges and furrows, concentric with the walls. The air is exhausted from this box, which is then hermetically sealed. The result is that the elastic cover rises and falls with every change in atmospheric pressure. By means of a combination of levers and springs, these movements are communicated from the center of the cover, to a pointer which moves over the graduated face of the dial, on which inches and hundreths are inscribed, which correspond with the height of the column in the mercurial instrument. The whole apparatus is encased in a brass box, about four inches in diameter, and two inches deep, covered with a front glass, and resembling, in general appearance, a chro

nometer case.

Having tested the barometer to my own entire satisfaction, and knowing others who have also done so, and being repeatedly assured that they have often saved

their cost in a single haying season, I give it a hearty commendation, and take this method to introduce it more generally to the notice of farmers. None should, however, expect that as a weather prophet the barometer will be found of unerring accuracy and exactness, for no infallible means of predicting approaching changes have yet been discovered. The state of the weather depends upon various conditions, of which the weight or density of the atmosphere is but onethe amount of moisture contained in it is another; temperature is a third; electrical changes a fourth, and so on. Then again local causes have much to do with the weather in any given locality. But in connection with the ordinary appearances in nature, which all persons more or less observe, and which from time immemorial have been recognized as indicating changes, the barometer renders exceedingly valuable assistance in judging; and the more so that its testimony touches a point which we have no other means of ascertaining, i. e. the density of the atmosphere at the time.

As before remarked, the average height of the barometer at the sea level is about thirty inches. As we ascend from this level the mercury falls, for the simple reason that we leave a portion of the atmosphere beneath us, and of course there is less weight above. Every hundred feet we rise the column falls about a tenth of an inch, so that it is no particular height which indicates either fair or foul weath-r-but we judge only by the changes.

Prof. Silliman gives the following rules which embody the results of long and various experience in different places:

1. When the mercury is very low high winds and storms are likely to prevail. 2. Generally, the rising of the mercury indicates the approach of fair weather; and its falling shows the approach of foul weather.

3. In sultry weather the falling of the mercury indicates thunder. In winter its rise indicates frost. In frosty weather its fall indicates thaw, and its rise indi

cates snow.

4. Whatever change of the weather suddenly follows a change in the barometer may be expected to last but a short time.

5. When the barometer alters slowly a long succession of foul weather may be expected, if the column falls, or of fair weather if it rises.

6. A fluctuating and unsettled state of the barometer indicates changeable weather.

In the above rules the index hand of the aneroid answers to the mercury column of the old barometer. Mr. Kendall furnishes the following rules:

1. There is no point at which the barometer must stand to indicate rain or wind.

2. The judgment must be governed by the rising or falling of the barometer. 3. The falling of the barometer indicates the approach of a storm, the extent of which will be proportionate to the amount and rapidity of the fall.

4. Showers. The barometer falls previously from four to twelve-hundreths of an inch, varying in time from one to three hours. The greater and more rapid the fall, the more violent will be the shower-accompanied more or less with wind.

5. North-easterly storms. The barometer falls previously from four to eighttenths of an inch, varying in time from one to four hours; and continues falling until the storm arrives at its crisis, when the barometer begins to rise, and continues rising until that part of the storm which comes from the north-west passes off.

6. Southerly storms. The barometer falls previously from one to four-tenths of an inch, varying in time from six to twelve hours. These storms generally precede unsettled weather; at such times the barometer continues low, and very slight additional depression are followed by rain.

A southerly storm is perhaps the most difficult to judge of by appearances, as they change so frequently without any real change in the atmosphere. During this class of storms the utmost confidence should be placed in the barometer.After the first indication as above, and the barometer does not rise but remains stationary, it is strong indication that the storm has not all passed.

The foregoing rules are the result of long and careful observation. It must be remembered that storms occur under different circumstances in different parts of the globe; yet, taking the first three of the above rules as a basis of calculation, a short experience, with the exercise of the judgment, will enable one to determine very correctly concerning approaching changes in the weather.-Agriculture of Maine, by S. L. Goodale.

In order to show how to find the mean height of the barometer, there it is necessary to observe its various oscillations from September to September, and from that to the first January, this being a period of sixteen months observations, during which we will be enabled to obtain five annual means. Thus the monthly means, from September to September, will at this rate express the first annual Those from October to October, the second; from November to November, the third; from December to December, the fourth; from January to January, the fifth. Also, when these five annual means are added together, and their product divided by five, the quotient will be the result of the mean height of the mercurial column proper to the height of its locality from the ocean.

mean.

To determine the height of localities above the level of the sea, we have the following:

Supposing the mean height of the barometer at a certain place had been found to be 29.54 inches, and the mean temperatnre 52 degrees.

As the barometric mean be always subject to a correction for temperature. which is due to the expansion of the mercury in the cistern, we therefore reduce the mean temperature to the freezing point, as follows:

1. Subtract 32 degrees from the mean temperature and divide its difference by 5.

OPERATION.

52

32

Divide 20 by 5, quot. 4.