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rometriMeaements.

Log. 30,000
Log. 14.895

1.4771213
1.1730405

Constant multiplier

Difference= .3040808

= 60000

Approximate elevation = 18244.848

cal Measurements.

In illustration of these rules, we shall subjoin some rection to be applied to the upper column is .0015 Barometrireal examples. General Roy, in the month of August × 30.6.=.045. Wherefore, 1775, observed the barometer on Caernarvon Quay, Examples, at 30,091 inches, the attached centesimal thermometer indicating 15.7, and the detached 15.6; while, on the peak of Snowdon, the barometer fell to 26.409 inches, and the attached and detached thermometers marked respectively 10°,0 and 8°,8. Here twice the difference of the attached thermometers is 11°.4, and twice the sum of the detached thermometer is 48°.8, which becomes 50.8, when augmented by the fifth part of the mean temperature on that parallel. Now, omitting the lower decimals, the first correction is .00264 x 11.4.030, to be added to 26.409. Wherefore,

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Difference = .0561416
Constant multiplier = 60000
Approximate height 3368.496

And, for the true height, the correction is 3.37 X
50.8 171.2, which gives 3340 for the final result.
We shall take another example from the observa-
tions made by Sir George Shuckburgh Evelyn, at
the same period, among the mountains of Savoy.
This accurate philosopher found the barometer,
placed in a cabin near the base of the Mole, and

only 672 feet above the surface of the lake of Ge

neva, to stand at 28,152 inches, while the attached
and detached thermometers indicated 16°.3 and 170.4;
but, another barometer carried to the summit of that
lofty insulated mountain, the mercury sunk to 24,176
inches, the attached and detached thermometers mark
ing 140.4 and 13°.4. Wherefore, twice the difference
of the degrees on the attached was 3°.8, and twice the
sum of the degrees on the detached thermometer was
61.6. Consequently, the correction to be applied
to the higher column was .0024 × 3.8 = .009, which
makes it 4.185. Now,

Log. 28,152

Log. 24,185

1.4495092
1.3835461
Difference = .0659631
Constant multiplier = 60000
Approximate elevation 3957-786

To correct this approximate elevation, remove the
decimal point three places back, and multiply it by
61.6, increased by 2°.9, the fifth part of the mean
temperature, corresponding to the latitude; but
3.96 × 64.5=255.4, and 3957.8 +255.44213.
Hence the summit of the Mole is 4885 feet above
the lake of Geneva, or 6083 feet above the level of
the Mediterranean Sea.

The last example we shall give is drawn from the
observation which Baron Humboldt made among the
Andes, near the summit of Chimboraço, the highest
spot ever approached by man. This celebrated tra-
veller found there, that the barometer fell to 14,850
English inches; the attached thermometer in the
tent being at 10°, and the detached in open air be-
ing 1.6o under zero. But the same barometer, carried
down to the shore of the Pacific Ocean, rose exactly
to 30 inches, while both the attached and detached
thermometers stood at 25°.3. Consequently the cor-

Now, the difference of the detached thermometers
or 26.9° being doubled and farther increased by
5.8°, the fifth part of the mean temperature at the
equator, makes 59°.6; the final correction to be ap-
plied is therefore 18.24 × 59°.6 = 1087, which
gives 19,332 feet for the true elevation observed, or
2140 feet below the summit of Chimboraço.

These calculations are performed by the help of Calculation
logarithms. It is desirable, however, to approxi- without Lo
mate at least to barometrical measurements with-garithms.
out such aid. A very simple rule for this ob-
ject has been given by Professor Leslie in his Ele-
ments of Geometry. Since Log. = 2 M

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a

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+

a-b
a+b+

where M denotes the modulus of the logarithmic system. When a approaches to b, the lower terms may be rejected without

a

sensible error, or Log. Z=2 M (2),

very near

a+b
ly. Wherefore, in reference to our atmosphere, the
modulus is expressed by the equiponderant column
26,058 feet, or only 26,000 in round numbers;
of homogeneous fluid, or 60,000 × .4342945 =
whence, as the sum of the mercurial columns is to
their difference, so is the constant number 52,000 feet
to the approximate height. Let General Roy's obser-
vation on Snowdon be resumed as an example: The
analogy is 30.091 + 26.439: 30.091-26.439, or
56.530: 3.652:: 52000: 3,359, the approximate ele-
vation, differing very little from the logarithmic result.

This mode of calculation may be deemed suffi-
ciently accurate for determining any altitude that
exceeds not 5000 feet. But it will extend to great-
er elevations, if the second term of the series be like-
wise taken; which is done by striking off three figures,
and cubing the half of this number. Thus, resum-
ing the mensuration of Chimboraço; 44.895:15.105
52,000:17,496, and (8.75)=670, making together
18,166 for a nearer approximation.

The calculation of barometrical measurements, in- Barometric cluding the corrections required, is rendered most Scale. easy and expeditious by means of a sliding rule made by Mr Cary, optician in London. This small instrument should always go along with mountain barometers, and it will be found a very agreeable companion to every geological traveller.

But portable barometers, in spite of every precaution, are yet so liable to be broken or deranged, that other auxiliary methods are desirable for ascertaining distant elevations. In this view, the variation of the boiling point of water was proposed by Fahrenheit, as far back as the year 1724, the idea having occurred to him, as it had done before to Amontons, while engaged with experiments to perfect his thermometer. Little regard, however, seems to have been paid to the sugges

cal Measurements.

Barometri- tion, till De Luc and Saussure made a series of observa tions on the heat of ebullition at different elevations above the surface. About thirty years since, Cavallo attempted to revive the scheme of Fahrenheit, but experienced much difficulty in preventing the irregular starts of the thermometer plunged in boiling water. The best and surest way of examining the heat of ebullition, is to suspend the bulb of the thermometer in the confined steam, as it rises from the water; and this mode, we understand, has very lately been resumed, with great prospect of success, by the Reverend Mr Wollaston.

Temperature of Boiling Water applied to the Mensuration of Heights.

The heat at which water boils, or passes into the form of steam, depends on the weight of the superincumbent atmosphere. By diminishing this pressure, the point of ebullition is always lowered. It appears that, while the boiling heat sinks by equal differences, the corresponding atmospheric pressure decreases exactly, or at least extremely nearly, in a geometrical progression; it being found that, every time such pressure is reduced to one half, the temperature of boiling water suffers a regular diminution of about eighteen centesimal degrees. This beautiful relation assimilates with the law which connects the density and elevation of the successive strata of the atmosphere. The interval noticed between the boiling points at two distinct stations must be proportional to their difference of altitude above the level of the sea. We have, therefore, only to determine the coefficient or constant multiplier; which may be discovered either from an experiment under the rarefied receiver of an air-pump, or from an actual observation performed at the bottom and on the top of some lofty mountain. We shall prefer at present the observation made by Saussure on the summit of Mont Blanc. This diligent philosopher found, by means of a very delicate thermometer constructed on purpose, that water which boiled at 101°.62 in the plain below when the barometer stood at 30.534 English inches, boiled at 86°.24 on the top of that mountain, while the barometer had sunk to 17.136. Wherefore the distance between the points of ebullition, or 15.38 centesimal degrees, must correspond to an approximate elevation of 15,050 feet; which gives 978 feet of ascent for each degree, supposing the mean temperature of the atmospheric column to be that of congelation. But it will be more convenient to assume 1000 for the constant multiplier, which corresponds to the temperature of 510.

To reduce this very simple result into practice, it would be requisite to have a thermometer with a fine capillary bore, and nicely constructed, the stem six or eight inches long, and bearing ten or a few more degrees from the boiling point; these degrees to be divided into twenty or perhaps fifty equal parts engraved on the tube, which should be rather thick, and terminating in a bulb of about half an inch diameter. This thermometer, being fitted with a brass ring two inches above the bulb, should screw into the narrow neck of a small copper flask, which holds some water, but has a hole perforated near the top for allowing the steam to escape. The water may be made to boil by the application of a lamp. The difference between the indications of the thermometers at the two stations being multiplied by a thousand feet, will give the elevation corresponding to a

temperature of 510. The correction for the actual Barometrimean temperature can easily be applied. If a more cal Meacorrect coefficient be afterwards determined, the surements. same thousand, retained as a multiplier, may easily be adapted to another temperature.

This method of measuring elevations on the sur-Mode of face of the globe is, therefore, capable of great im- tracing Ver. provement, and might be employed with advantage tical Secin a variety of cases where observations with the ba-tions. rometer are not easily obtained. Its application would be most important to physical geography, in ascertaining the capital points for tracing the outline of the profile or vertical section of any country. The common maps, which exhibit mere superficial extension, are quite insufficient to represent the great features of nature, since the climate and productions of any place depend as much on its elevation above the sea as its latitude. Scientific travellers have accordingly turned their attention of late years to the framing of vertical sections. As a specimen, we give in fig. 22, from Humboldt's Geography of Plants, a section across the American Continent, one of the best and most interesting that has yet appeared. It consists, in fact, of four combined sections, traversing through an extent of 425 miles. The line begins at Acapulco on the shore of the Pacific Ocean, and runs 195 miles, about a point of the compass towards the East of North, to the city of Mexico; then 80 miles, a point to the South of East, to La Puebla de los Angeles; again it holds a North-East direction of 70 miles, to the Cruz Blanca; and finally bends 80 miles East by South, to Vera Cruz, on the coast of the Atlantic. A scale of altitudes is annexed, which shows the vast elevation of the table-land of Mexico. An attempt is likewise made in this profile to give some idea of the geological structure of the external crust. Limestone is represented by straight lines slightly inclined from the horizontal position: Basalt, by straight lines slightly reclined from the perpendicular: Porphyry, by waved lines somewhat reclined: Granite, by confused hatches: Amygdaloid, by confused points.

the level of

By this mode of distant levelling, a very interest- The Casing discovery, in another quarter of our globe, has plan below been recently made by Engelhardt and Parrot, two the Ocean. Prussian travellers. They proceeded, on the 13th July 1814, from the mouth of the Kuban, at the island of Taman, on the Black Sea; and, examining carefully every day the state of the barometer, they advanced with fifty-one observations, the distance of 990 wersts, or 711 English miles, to the mouth of the Terek, on the margin of the Caspian Sea. Similar observations were repeated and multiplied on their return. From a diligent comparison of the whole, it follows that the Caspian is 334 English feet below the level of the Black Sea. That the Caspian really occupies a lower level than the Ocean, had been suspected before, from a comparison of some registers of barometers kept at St Petersburg, and on the borders of that inland sea; but the last observation places the question beyond all doubt. It farther appears, that within 250 wersts, or 189 miles, of the Caspian, the country is already depressed to the level of the Ocean, leaving, therefore, an immense bason, from which the waters are supposed to have retired by a subterranean percolation. (D.)

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Barracks.

Historical Notices.

ports respecting Barracks.

BARRACKS. Till the middle of the year 1792, when there was a prospect of a war with revolutionary France, and the British ministry were apprehensive of disturbances in this country, barracks were neither very numerous, nor were they under the control and management of a separate and peculiar Board. Till that time, they were built under the authority and directions of the Board of Ordnance, by whom they were supplied with bedding and the necessary utensils. Any extra articles that were requisite were supplied by the secretary at war. In 1792, orders were given by the ministry to build cavalry barracks with the utmost despatch, and the deputy-adjutant-general was directed to superintend the building and fitting them up. In January 1793, he was appointed superintendant-general of barracks; and, on the 1st of May that year, the King's warrant was issued for their regulation. Greater powers were given to the superintendant-general in the year 1794; but as these seemed to interfere with the duties and powers of the Board of Ordnance, a new warrant was issued in the year 1795, defining and limiting the respective duties and powers of the Board of Ordnance, and the superintendant-general, or barrack-master-general, as he was now called. In the year 1796, the barrack-office establishment consisted of a barrack-master-general, with two clerks; a deputy-barrack-master-general; an assist ant-barrack-master-general, with three clerks; an accountant, with five clerks; an assistant-barrack master-general for the general inspection of barracks, and six other assistant-barrack-masters-general for the particular inspection of barracks in different districts; five clerks for general business; one assistant-barrack-master-general for the building branch; one checking clerk, and seven other clerks; two architects and surveyors; one assistant-barrack. master-general in North Britain; with two assistants and clerks; one treasurer; and three other assistantbarrack-masters-general for general duties, and visiting barracks. The salaries and extra pay of these officers amounted, in 1796, to L. 9524, 178. 2d. The establishment was afterwards considerably increased, in proportion as the number of barracks throughout the kingdom increased, and by the creation of some new officers, among whom was a law clerk. In 1806, the salaries amounted to L. 19,329, 48. 10d.

Official Re. During this year, the commissioners of military inquiry began their duties; and their first reports were on the subject of the barrack establishment: In the arrangement of this establishment, and in the mode in which its duties were performed, particularly with respect to the supplies of coals, &c. to the different barracks, and the contracts for building them, they pointed out many things that were highly objectionable; and concluded their reports by recommending that the offices of barrack-master-general, and deputy-barrack-master-general, should be totally abolished, and that the superintendence of the barrack establishment should be vested in commissioners. This suggestion, and some others relative to the mode of transacting the business of the department, and preventing useless and extravagant expenditure, have been followed; and the barrack establishment is now angement. under the direction of four commissioners, one of

New Ar

VOL. II. PART I.

whom is generally a military man. The mode of Barracks writing letters in this public department is deserving of notice and imitation, as securing despatch and ac curacy. A sheet of paper being folded in the middle, officers of the department, who address the barrack-office, write their letters on the left side; and, along with the original letter, send a duplicate in the same form, and signed also. On the blank side of the duplicate is written the official answer from the barrack-office which is sent; and, on the original letter, which is preserved in the office, is copied the answer: each party has thus an exact copy of the whole correspondence.

the De

As it frequently happened, that it was absolutely Clanse in necessary to build barracks on an emergency, when fence Act there was no time to summon a jury to value the respecting land before the commencement of the building, and Barracks, as most persons were averse to have barracks near their dwelling-houses, or even on their property, Government was often obliged to pay an extravagant price for the land which they needed for their erection; in order to remedy this evil, it was provided by the act, usually called the defence act, 43d Geo. III. cap. 55, that Justices of the Peace might put any general officer into the possession of such ground as he might deem fit for the erection of barracks;-the value of it to be settled afterwards by a jury;-provided, however, the necessity for such ground was certified by the Lord-Lieutenant, or two Deputy-Lieutenants of the county.

Barracks throughout the country are more immediately under the management and care of the assistant-barrack-masters-general, and the resident barrack-masters; the former are attached to districts; the latter to particular barracks. The following are the districts in Great Britain :

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