« ElőzőTovább »
Meteot Reaumur at the same time sinking only 10:6. The se- watery store, the moisture precipitated would cover the
ology. okupio cond observation, it should be remarked, was made in the surface of the earth only to the small depth of 7} midst of the glacier of Hautema, and it is therefore pro- inches, and in the mean parallel of 45° only about 3}
Depth of bable the ice and snow with which it was covered sup- inches. Supposing the whole atmosphere, from a water if si by sure" plied this extraordinary humidity. And this opinion is state of absolute dampness, were to discharge its entire atmosphere confirmed by another observation which he made on a watery store, it would only form an uniform sheet of were to dis
charge its projecting rock seven toises less elevated, and where about 44 inches in depth. To furnish a sufficient supply he found the humidity 14°7 less than at the lowest of rain therefore, as Leslie remarks, it was necessary the
watery station, agreeing, therefore, with the general principle air should undergo very frequent changes from dryness store. before advanced. In another observation, however, to humidity in the course of the year. Supposing the Saussure is not disposed to attribute all this difference mean quantity of water existing in a state of vapour in to the ice. Another example is also given by the same an atmospheric column, having a square inch for its indefatigable and accurate observer. In the middle of base, to amount to about 4 cubic inches, we may infer, the glacier of Miage, his hygrometer indicated a hu- that the quantity actually existing in the whole atmomidity of 81o.1, but on the Col de la Seigne, 186 toises sphere amounts to about 12,500 cubic miles. above the glacier, it indicated 100°, though the decre- (455.) Such results, however, must be truly regarded Such con
ment of temperature 30.3 according to Saussure's table, as approximations, and adopted only to enable us to clusions, Tiger ought to have indicated only a humidity of 89°.9. It catch a glimpse of the mysterious phenomena of Na- however, set.bas sometimes happens, therefore, that vapour is more ture. We know too little of the humidity of the lower
truly remert abu-abundant on the summit of a hill than in the valleys at regions of the atmosphere, to speak with certainty of garded as act on the
its base; but as the exceptions are not numerous, and any of the phenomena connected with the higher. We approximen in the may be explained by the influence of peculiar loca- know too little of the phenomena which may be said to mations. zig ben lities, we may in general conclude, that the absolute be continually within our grasp, to permit us, without
quantity of vapour in the air diminishes as we ascend. the exercise of the greatest caution, to apply them even It should be borne in mind in considering this part of as humble approximations to those lofty regions of the the subject, that the anomalies we have before proved to air, which as yet have defied the aspiring
ambition of exist in the temperature of the air at different elevations, Of this, however, we are certain, that the higher must necessarily impart a like irregularity to its humi- regions of the atmosphere are comparatively drier than dity.
those below. Colonel Beaufoy, in his interesting ascent (454.) It would be possible to compute approxima- of Mont Blanc, remarks, “ that the air itself was thirsty, a tiem tively the actual weight of vapour contained in any of its extreme dryness," said he,“ had robbed my body of
the atmospheric columns, and if necessary the whole its moisture." und quantity of moisture contained in the atmosphere. The (456.) The vapour actually existing at any time in Moisture stre com experiments of Biot and Arago have determined that the air is far however from being equally distributed in not equally 23, and the weights of equal volumes of vapour and air at the those volumes of it which possess the same degree of
in volumes temperature of the boiling point, and when both are temperature. A given volume of it, at the temperature of same subject to the same pressure of .76 metres, are as of 50°, in a portion of the atmospheric column reared
tempera-589481 to .9454476, or as 5 to 8 nearly; and since above Plymouth, may possess a very different degree of ture. both are affected in their bulk in the same manner, by humidity from a volume of a like temperature above Case of every alteration of temperature and pressure, the same Prague. The former, from its peculiar locality, may be Plymouth invariable relation may be supposed to be preserved, in a state of high saturation, whereas the other, in the and Prague. so long as the vapour retains its elastic form. In heart of a great continent, and governed by a wind from some inquiries of this sort it has been assumed, that a different quarter, may be comparatively dry. It is the mean point of deposition for the globe in general, not equality of temperature alone that we must seek for, is about 6° below the average temperature, -though in applying practically the elements of the problem now this assumption, from the limited nature of the obser- under review, but the quantity of moisture coexisting vations from which it is deduced, cannot be received with it. To-day, the air of Moscow may afford a greater Moscow without caution; and if we adopt in addition another proportion of moisture than the warmer atmosphere of and Ispahypothesis, by supposing the same invariable difference Ispahan, and to-morrow the relation may be entirely han. of temperature to be maintained, throughout all the reversed. Contending winds not only influence the atmospheric strata, we may make an approximation to temperature and pressure of the air, but its humidity the whole quantity of moisture contained in the atmo- also; and the peasant of our own country is familiarized spheric columns, by means of the formula
with their different effects, One breeze may bring to
him gentle and fertilizing showers, and another may
burn up the produce of his farm.
(457.) But we need not go to the atmospheric Different wherein f denotes the elastic force of vapour at a tem. columns of different countries to seek for diversities of quantities perature six degrees below the mean temperature of the moisture, since like anomalies are sometimes to be found of moisture place of observation, and the numerator 407.4 the
in same at in different strata of the same column. Saussure reheight in inches of a column of water equivalent in
mospheric marked that his hygrometer, near the surface of the
column. weight to the mean condition of a corresponding earth, often proved the air to be removed 30 or 40 column of the air, and the numerical value of which degrees from extreme saturation, when the presence of formula, will give the mean height in inches of a column clouds in the upper sky demonstrated the entire humiof water, equal to the whole moisture contained in a dity of that region. That eminent observer often re- Effects of column of the atmosphere, standing on the same base. marked this phenomenon when he ascended a mountain clouds. In this way we may compute, that if the atmospheric whose summit was enveloped in a cloud. On the other Of mists. columns at the Equator were to discharge their whole hand he as frequently observed, that when mists covered
Meteor- the plains, and a bright sun gilded the summits of his perhaps from the mean results lines of equal humi- Meteor. ology. noble mountains, the limit of extreme humidity was to dity.
be found below, and air far removed from saturation (460.) It is a great practical problem therefore now
respecting swim between masses of air necessarily less humid than discover, if possible—and what will not united labour Actual the clouds themselves, Of the effects of clouds in and Philosophical enterprise effect,—some accurate rela- dity of the example of humidity of
augmenting the humidity of the atmosphere, he has tions respecting the distribution of moisture; to trace atmosphere a cloud.
one conclusive observation. When on the summit of some of the varying conditions of humidity, which, for
enveloped in a cloud, the humidity increased to 949.6. but with all the important processes of agriculture. At What we Elastic (458.) Mr. Daniell has also deduced, both from the present moment we can do little more than say, present force of theory and the actual experiments of Captain Sabine, that of this wide-spreading ocean of vapour, we can vapour that the elasticity of vapour does not diminish in an merely estimate its elastic force and quantity at a given humidity
specting the dues not diminish
uniform manner, according to the decrease of tempera- time, and in a general way trace an analogy between of the atuniformly ture and density of the air, but the dew.point re- the course of its changes, and the progress of the mean mosphere.
mains stationary to a great height, and then suddenly temperature of the year. We know not where to look for Not able ! ascend. falls to a large amount. At Sierra Leone, the dew- the data which will enable us to contrast Philosophically contrast t) point at the level of the sea was found to be 70', and at the humidity of different climates, to measure the influ- humidity
different the same hour upon the summit of the Sugar Loaf ence of mountains and valleys in modifying the condi.
climates. mountain, 2520 feet above, it was found exactly the tions of vapour, the sea which exercises its own peculiar Examples. same. At Jamaica also, by the sea-side, the tempera. laws, and the islands and continents which diversify in
ture of the air was 80°, and the point of deposition 73° ; so great a degree all the phenomena of humidity.
with land Mr. Green the aeronaut also found, when ascending may be divided generally into two classes: the land and sea from Portsea, that at an elevation of 9890 feet, the dew- winds blowing from off the great continent of Europe, winds. point was 64°, the same as at the surface of the earth; and which comprise the North-East, East, and Southbut at 11,060 feet it fell to 32°, making a difference of East ; and the sea winds passing over the waters which thirty-two degrees in a little more than 1100 feet; surround us on every side, the North, North-West, affording a decisive example, as Mr. Daniell observes, West, South-West and South. In the former we might of an immense bed of vapour rising in its circumambient expect to find the course of the mean temperature inedium, unaffected by decrease of density or tempera- exactly followed, because the sources which supply the ture, till checked by its point of precipitation; and also vapour must be comparatively shallow streams and re
of an incumbent bed of not much more than one-third servoirs of water, whose temperature readily adapts Proofs the density, regulated, no doubt, as the last, by its itself to that of the surrounding air; but in the unwhich they owu point of deposition in loftier regions. Such pheno. fathomable depths of the great ocean which affords afford of the mena afford strong experimental evidence of the mecha- humidity to the latter, the peculiar law by which the mechanical mixture of
nical mixture of the aqueous particles in the atmosphere, density of water is governed, must at particular periods vapour with and admit of no explanation by any law analogous to maintain a temperature above that of the declining seaair. that of chemical solution.
son, whilst at others, the increasing heat of the latter Want of (459.) We have before lamented the want of correct must outstrip the progress of the former. practical observations to assist us in our inquiries respecting tem- (462.) Here then is a single problem, the elements observa
perature; and with equal reason may we deplore the ab- of which must vary with every locality. Swisserland, tions.
sence of accurate and extended results to illustrate the surrounded on all sides by mountains, must present
isothermal lines, so, had this hygrometer existed a cen- March, and which is diminished to three degrees Lines of tury ago and been diligently applied, might we have in April and May. In June they again attain equal hus
traced some of the singular mutations of the great their former equality, because the temperature corremidity.
ocean of vapour which surrounds us, and have deduced sponding to the maximum density, caunot be lowered
N.E. E. S.E.
N. N.W.W. S.W. S.
Metedre till the whole mass of waters has passed this limit; and By attending to the results of this Table we may first Meteor clogy in the deep seas this must necessarily be a process of observe a constant difference of the temperature of the ology.
some duration. The shallow waters on the contrary, Dew point to prevail from September to December, in
cess of thawing, preventing that accession of tempera-
vapour rapidly regains its former relative degree of
force, imparting considerable increments to both classes Table XCVII.
of winds in June and July, until their maximum conOf the Difference of the Dew Point in the Land and ditions are obtained in August
, and are followed of Sea Winds.
course by a decline of both in September.
(464.) We must now take a hasty glance at the Mean reLand Winds. Sea Winds.
few imperfect results we are able to offer respecting the sults of dise Months.
distribution of aqueous vapour during the successive tribution of September
seasons of the year, still, of necessity, limiting our inquiries aqueous
vapour in to the locality of London.
successive November 41
: Beginning with January, the time at which the minimum seasons of December
temperature prevails, Mr Daniell found, from a mean of the year for January
three years' observations, and a triple observation each London. February
day, the mean elastic force of the vaporous atmosphere
to be also at its lowest point, and represented by, 0.234
inches of quicksilver, the mean temperature being at the
same time 36°.1. As the mean temperature advances
through the month of February to 38°, the force of
vapour increases feebly to 0.239 inches. With the
month of March, however, the mean temperature is Lesce CH (463.) The peculiar locality of Great Britain may augmented nearly six degrees, the elastic force of the w Polare also be supposed in another way to modify the vapour advancing at the same time to .272 inches. In
the kimidts of
production of vapour, by its having to the North, at April the mean temperature of the air rises to 490.9,
the advance of the mean temperature and humidity are
nearly uniform, the former being 58o.7, and the force of TABLE XCVIII.
vapour .410 inches. Through July, the moisture ang
ments with rather greater rapidity than the temperaOf the Effect of the Ice in the North Seas upon the
ture, the elastic force being .468 inches, and the mean
temperature 61°. In August, these phenomena continue
nearly the same, the force of vapour being .481 inches,
and the mean temperature 61°.6. During September, September
the reduction of temperature is first felt sensibly, its
mean sinking to 57°.8, the vapour at the same time
declining to .432 inches. In October, the mean tem-
perature falls to 48o.9, and the elastic force to .336.
During the dark and dreary month of November, the
atmosphere becomes nearly saturated with moisture,
the mean temperature falling to 42o.9, and the mean
elasticity of vapour to .286 inches. December ex-
hibits nearly the same characteristics, the mean tem-
perature being 390.3, and the elastic force of vapour
(465.) The preceding abstract forms, as
Meteor-' stated, the mean results for the respective months; but tity of vapour existing in the air ; and as through the Meteorology. what, it may be asked, are the aberrations exhibited changes of the year, the mean temperature rises and
ology. during each, by particular winds ? a cause which is for falls, in a general way it is found that the quantity of Aberrations
ever modifying all the phenomena of vapour. The fol- vapour in the air must rise and fall with it. In very from the mean re
lowing maximum and minimum temperatures of the short intervals, it is true that aberrations may present sul Dew point peculiar to each month, have been deduced by themselves apparently in opposition to the Principle Mr. Daniell.
which has been advanced, but on a great scale it may be
clearly and satisfactorily traced. TABLE XCIX.
(469.) It is also worthy of observation, that if the Changes of pressure of the aqueous vapour be separated from that of pressure of the aerial, it will in general be found to exhibit changes
air opposite directly opposed to the latter. This can be best disTemper. Temper
trate the two, it will be found that the undulations of
the curve representing the pressure of the whole atmo-
by a fall in the barometric curve, and vice versa.
54.0 S. 40.5 N. E.
62.0 S. 49.5 N. or N. E. (470.) Another method, however, of a very different
regarding the elastic force of vapour, its density, and the
law of its dilatation, as so many independent elements to November 48.0 S.
35.5 N. W. be found, and by an operation connected with some December. 45.5 S. 27.5
functions of the density and temperature, to discover
time or place, an attempt has been made to connect the Attempts to Monthly (466.) Mr. Daniell has graphically illustrated some indications of an instrument with the tensions of vapour connect the results. of his interesting results. In fig. 4, we have an exam at different temperatures, and thence to deduce all the indications
of an instruple of the monthly progress of the mean tempera- hygrometric conditions of the air. Saussure first endea
ment with ture and mean Dew point. The full line exhibits the voured to establish a relation of this kind, but it is to the quan. progress of the former, and the dotted line that of the the later labours of Gay Lussac that we would now tity of valatter, the degree of dryness belonging to each period especially refer. Of the two methods we certainly pre
in the air. being accurately represented by the interval between the fer the former, but we owe to our readers an explicit Relation of two curves. We may hence perceive how closely the account of the latter. vapour and constituent temperature of the vapour follows the mean (471.) To accomplish this object, the celebrated Che- Gay Lussac perature of temperature of the air, by the general resemblance of mist alluded to procured one of Saussures Hygro- employed
Saussure's the year. the two curves ; and also how clearly they exhibit the meters, as accurately and delicately made as the circum
hygrometer comparative dryness of the Spring and summer months, stances of its construction would permit; and placed it for this purand the dampness of the autumn and winter.
in a receiver containing some water, or a solution of a pose. Diurnal (467.) In fig. 5, which has also been derived from Salt of a known Specific Gravity, and then observed the results.
Mr. Daniell, this general accordance of the mean tem- degree which the instrument marked, under the circum-
him at the duced from observations made four times each day, the temperature of 10° of the Centigrade scale, the ten
temperatogether with the daily maxima and minima. An accu- sions of the liquids employed being expressed in parts of ture of ten rate inspection of this last figure most clearly demon- the tension of pure water, which was represented by centesimal strates that there is but little relation between the maxi 100.
degrees. mum temperature and the elastic force of the vapour, Relation of vapour and
and that the vapour appears to be governed principally minimum by the daily minima, thus practically confirming the tempera principle before advanced on the authority of Dr. Anture. derson.
(468.) That the quantity of vapour existing in the atmosphere near the level of the sea, must follow the course of the mean temperature during the successive seasons of the year, may also be inferred from the consideration, that the existence and quantity of vapour in the air, must be governed entirely by its temperature, and that the rate of evaporation is dependent on the same cause. Hence it follows, that whatever influences the temperature, must at the same time affect the quan
Specific Tension of the Gravity at Solution at 100 the Temper. of the Centesimal ature of 10° of Scale, that of the Cen
Water being tesimal represented by Scale.
y=1 – (r) +
x + y 1
1163 82.3 92.2 (474.) If we select, by way of application, the third Numerical
result given in the Table for the muriate of lime, and example, Muriate of Lime. 1274 66.0 82.0
the density of which is 1397, we shall have according to
the limitation before assigned to the abscissæ
x = 0.376,
y = 0.613,
and which being substituted in the last equation will
0.011 y' :
0.00777818; (472.) The relation of these results may, however, Graphic Lokation be more clearly explained by means of a graphic and this being so minute a quantity, the point in the dibesame illustration. For this purpose their author had re
curve to which it refers, may, without any sensible course to a curve whose coordinates u and y should
error, respectively denote the tensions and hygrometric de. But to avoid any unnecessary error, the origin of
be regarded as the vertex of the hyperbola. grees observed. At the origin of this curve, the values the abscissa x' may be assumed at that point of the axis, of r and y were to be severally zero, because that point where the latter is intersected by y'; and then the value of the hygrometric scale answered to extreme dryness ; of (x) may be found by adding 0.376 to the projection and at the other extremity of the scale, the same coordinates were to be respectively equivalent to 100, of y' on the axis of «, or in other words, to y cos x, or because 100 degrees of the hygrometer corresponded to
0.0054996, and which will hence give complete saturation. Between these limits, the experi
(r) = 0.3814996, misse cor- mental results obtained by Gay Lussac afforded many thus determining completely the relations of the two e regions intermediate points for the curve, and which upon in- systems of coordinates. Hence we shall obtain the two e'lypto- vestigation he found to be a hyperbola, having its con- equations zeic le cavity turned towards the line represented by r, and its
x' = (x -0.3815) ✓ 2 - y', axis inclined in an angle of 45°, forming the diagonal and wypadda,
of a square whose base was the abscissa x= 100, and altitude the ordinate 100 corresponding to x = 0; the
V 2 hyperbola being thus symmetrically disposed with re
When x and y are both given, we can readily obtain the spect to the two sides of the square. This result we may renture to say could have scarcely been anticipated tuted in the former of these last equations, will give the
value of y' as before illustrated; and this being substi-
Table has been computed.
0.000 0.000 +0.167384 -0.707107 and
0.122 0.253 +0.074953 -0.441942 y = (3) + 72 (34–).
0.376 0.613 0.000000 -0.007778 These equations, however, may be simplified, by representing by unity the abscissa x corresponding to the
(475.) These elements are sufficient to determine the Equation of tension 100, and which assumption will enable us to obtain the expression nature of the hyperbola. For since its axis coincides the hyper
bola. with the line on which the abscissæ & are reckoned, its y=1- x; and since the primitive ordinates' (x) and (y) are simi- equation must be necessarily of the form larly related, we shall in like manner obtain
y = a + 2 bx! + cx', (y)=1- (x).
the values of the constant coefficients being determined The general equations above given will thus assume the by the respective values of x' and y' in the Table. Thus forms of
we shall obtain
y' =*+y - 1