The hour whose temperature coincides with the mean of the day necessarily varies with the distribution of cloud and sunshine; it is usually about 7 a.m. and 7 p.m.; whereas in Calcutta the same coincidence occurs at a little before 10 a.m., and in England at about 8 a.m.
Next to the temperature of the air, observations on that of the earth are perhaps of the greatest value; both from their application to horticulture, and from the approximation they afford to the mean temperature of the week or month in which they are taken. These form the subject of a separate chapter.
Nocturnal and solar radiation, the one causing the formation of dew and h.o.a.r-frost when the air in the shade is above freezing, end killing plants by the rapid abstraction of heat from all their surfaces which are exposed to the clear sky, and the other scorching the skin and tender plants during the day, are now familiar phenomena, and particularly engaged my attention during my whole Indian journey. Two phenomena particularly obstruct radiation in Sikkim--the clouds and fog from the end of May till October, and the haze from February till May. Two months alone are usually clear; one before and one after the rains, when the air, though still humid, is transparent. The haze has never been fully explained, though a well-known phenomenon. On the plains of India, at the foot of the hills, it begins generally in the forenoon of the cold season, with the rise of the west wind; and, in February especially, obscures the sun"s disc by noon; frequently it lasts throughout the twenty-four hours, and is usually accompanied by great dryness of the atmosphere.
It gradually diminishes in ascending, and have never experienced it at 10,000 feet; at 7000, however, it very often, in April, obscures the snowy ranges 30 miles off, which are bright and defined at sunrise, and either pale away, or become of a lurid yellow-red, according to the density of this haze, till they disappear at 10 a.m.
I believe it always accompanies a south-west wind (which is a deflected current of the north-west) and dry atmosphere in Sikkim.
The observations for solar radiation were taken with a black-bulb thermometer, and also with actinometers, but the value of the data afforded by the latter not being fixed or comparative, I shall give the results in a separate section. (See Appendix K.) From a mult.i.tude of desultory observations, I conclude that at 7,400 feet, 125.7 degrees, or + 67 degrees above the temperature of the air, is the average maximum effect of the sun"s rays on a black-bulb thermometer*
[From the mean of very many observations, I find that 10 degrees is the average difference at the level of the sea, in India, between two similar thermometers, with spherical bulbs (half-inch diam.), the one of black, and the other of plain gla.s.s, and both being equally exposed to the sun"s rays.] throughout the year, amounting rarely to + 70 degrees and + 80 degrees in the summer months, but more frequently in the winter or spring. These results, though greatly above what are obtained at Calcutta, are not much, if at all, above what may be observed on the plains of India. This effect is much increased with the elevation. At 10,000 feet in December, at 9 a.m., I saw the mercury mount to 132 degrees with a difl: of + 94 degrees, whilst the temperature of shaded snow hard by was 22 degrees; at 13,100 feet, in January, at 9 a.m., it has stood at 98 degrees, diff.
+ 68.2 degrees; and at 10 a.m., at 114 degrees, diff. + 81.4 degrees, whilst the radiating thermometer on the snow had fallen at sunrise to 0.7 degree. In December, at 13,500 feet, I have seen it 110 degrees, diff. + 84 degrees; at 11 a.m., 11,500 feet; 122 degrees, diff: + 82 degrees. This is but a small selection from many instances of the extraordinary power of solar radiation in the coldest months, at great elevations.
Nocturnal and terrestrial radiation are even more difficult phenomena for the traveller to estimate than solar radiation, the danger of exposing instruments at night being always great in wild countries.
I most frequently used a thermometer graduated on the gla.s.s, and placed in the focus of a parabolic reflector, and a similar one laid upon white cotton,* [Snow radiates the most powerfully of any substance I have tried; in one instance, at 13,000 feet, in January, the thermometer on snow fell to 0.2 degree, which was 10.8 degrees below the temperature at the time, the gra.s.s showing 6.7 degrees; and on another occasion to l.2 degrees, when the air at the time (before sunrise) was 21.2 degrees; the difference therefore being 20 degrees.
I have frequently made this observation, and always with a similar result; it may account for the great injury plants sustain from a thin covering of ice on their foliage, even when the temperature is but little below the freezing-point.] and found no material difference in the mean of many observations of each, though often 1 degree to 2 degrees in individual ones. Avoiding radiation from surrounding objects is very difficult, especially in wooded countries. I have also tried the radiating power of gra.s.s and the earth; the temperature of the latter is generally less, and that of the former greater, than the thermometer exposed on cotton or in the reflector, but much depends on the surface of the herbage and soil.
The power of terrestrial, like that of solar radiation, increases with the elevation, but not in an equal proportion. At 7,400 feet, the mean of all my observations shows a temperature of 35.4 degrees.
During the rains, 3 degrees to 4 degrees is the mean maximum, but the nights being almost invariably cloudy, it is scarcely on one night out of six that there is any radiation. From October to December the amount is greater = 10 degrees to 12, and from January till May greater still, being as much as 15 degrees. During the winter months the effect of radiation is often felt throughout the clear days, dew forming abundantly at 4000 to 8000 feet in the shaded bottoms of narrow valleys, into which the sun does not penetrate till 10 a.m., and from which it disappears at 3 p.m. I have seen the thermometer in the reflector fall 12 degrees at 10 a.m. in a shaded valley.
This often produces an anomalous effect, causing the temperature in the shade to fall after sunrise; for the mists which condense in the bottom of the valleys after midnight disperse after sunrise, but long before reached by the sun, and powerful radiation ensues, lowering the surrounding temperature: a fall of 1 degree to 2 degrees after sunrise of air in the shade is hence common in valleys in November and December.* [Such is the explanation which I have offered of this phenomenon in the Hort. Soc. Journal. On thinking over the matter since, I have speculated upon the probability of this fall of temperature being due to the absorption of heat that must become latent on the dispersion of the dense ma.s.ses of white fog that choke the valleys at sunrise.] The excessive radiation of the winter months often gives rise to a curious phenomenon; it causes the formation of copious dew on the blanket of the traveller"s bed, which radiates heat to the tent roof, and this inside either an open or a closed tent. I have experienced this at various elevations, from 6000 to 16,000 feet. Whether the minimum temperature be as high as 50 degrees, or but little above zero, the effect is the same, except that h.o.a.r-frost or ice forms in the latter case. Another remarkable effect of nocturnal radiation is the curl of the alpine rhododendron leaves in November, which is probably due to the freezing and consequent expansion of the water in the upper strata of cells exposed to the sky. The first curl is generally repaired by the ensuing day"s sun, but after two or three nights the leaves become permanently curled, and remain so till they fall in the following spring.
I have said that the nocturnal radiation in the English spring months is the great obstacle to the cultivation of many Himalayan plants; but it is not therefore to be inferred that there is no similar amount of radiation in the Himalaya; for, on the contrary, in April its amount is much greater than in England, frequently equalling 13 degrees of difference; and I have seen 16 degrees at 7,500 feet; but the minimum temperature at the time is 51 degrees, and the absolute amount of cold therefore immaterial. The mean minimum of London is 38 degrees, and, when lowered 5.5 degrees by radiation, the consequent cold is very considerable. Mr. Daniell, in his admirable essay on the climate of London, mentions 17 degrees as the maximum effect of nocturnal radiation ever observed by him. I have registered 16 degrees in April at Dorjiling; nearly as much at 6000 feet in February; twice 13 degrees, and once 14.2 degrees in September at 15,500 feet; and 10 degrees in October at 16,800 feet; nearly 13 degrees in January at 7000 feet; 14.5 degrees in February at that elevation, and, on several occasions, 14.7 degrees at 10,000 feet in November.
The annual rain-fall at Dorjiling averages 120 inches (or 10 feet), but varies from 100 to 130 in different years; this is fully three times the amount of the average English fall,* [The general ideas on the subject of the English rain-fall are so very vague, that I may be pardoned for reminding my readers that in 1852, the year of extraordinary rain, the amounts varied from 28.5 inches in Ess.e.x, to 50 inches at Cirencester, and 67.5 (average of five years) at Plympton St. Mary"s, and 102.5 at Holme, on the Dart.] and yet not one-fourth of what is experienced on the Khasia hills in Eastern Bengal, where fifty feet of rain falls. The greater proportion descends between June and September, as much as thirty inches sometimes falling in one month. From November to February inclusive, the months are comparatively dry; March and October are characterised by violent storms at the equinoxes, with thunder, destructive lightning, and hail.
The rain-gauge takes no account of the enormous deposition from mists and fogs: these keep the atmosphere in a state of moisture, the amount of which I have estimated at 0.88 as the saturation-point at Dorjiling, 0.83 being that of London. In July, the dampest month, the saturation-point is 0.97; and in December, owing to the dryness of the air on the neighbouring plains of India, whence dry blasts pa.s.s over Sikkim, the mean saturation-point of the month sometimes falls as low as 0.69.
The dew-point is on the average of the year 49.3 degrees, or 3 degrees below the mean temperature of the air. In the dampest month (July) the mean dew-point is only eight-tenths of a degree below the temperature, whilst in December it sinks 10 degrees below it.
In London the dew-point is on the average 5.6 degrees below the temperature; none of the English months are so wet as those of Sikkim, but none are so dry as the Sikkim December sometimes is.
_On the weight of the atmosphere in Sikkim; and its effects on the human frame._
Of all the phenomena of climate, the weight of the atmosphere is the most remarkable for its elusion of direct observation, when unaided by instruments. At the level of the sea, a man of ordinary bulk and stature is pressed upon by a superinc.u.mbent weight of 30,000 pounds or 13.5 tons. An inch fall or rise in the barometer shows that this load is lightened or increased, sometimes in a few hours, by nearly 1,000 pounds; and no notice is taken of it, except by the meteorologist, or by the speculative physician, seeking the subtle causes of epidemic and endemic complaints. At Dorjiling (7,400 feet), this load is reduced to less than 2,500 pounds, with no appreciable result whatever on the frame, however suddenly it be transported to that elevation. And the observation of my own habits convinced me that I took the same amount of meat, drink, sleep, exercise and work, not only without inconvenience, but without the slightest perception of my altered circ.u.mstances. On ascending to 14,000 feet, owing to the diminished supply of oxygen, exercise brings on vertigo and headache; ascending higher still, la.s.situde and tension across the forehead ensue, with retching, and a sense of weight dragging down the stomach, probably due to dilatation of the air contained in that organ. Such are the all but invariable effects of high elevations; varying with most persons according to the suddenness and steepness of the ascent, the amount and duration of exertion, and the length of time previously pa.s.sed at great heights. After having lived for some weeks at 15,300 feet, I have thence ascended several times to 18,500, and once above 19,000 feet, without any sensations but la.s.situde and quickness of pulse;* [I have in a note to vol. ii. chapter xxiii, stated that I never experienced in my own person, nor saw in others, bleeding at the ears, nose, lips, or eyelids.] but in these instances it required great caution to avoid painful symptoms. Residing at 15,300 feet, however, my functions were wholly undisturbed; nor could I detect any quickness of pulse or of respiration when the body was at rest, below 17,000 feet. At that elevation, after resting a party of eight men for an hour, the average of their and my pulses was above 100 degrees, both before and after eating; in one case it was 120 degrees, in none below 80 degrees.
Not only is the frame of a transient visitor unaffected (when at rest) by the pressure being reduced from 30,000 to 13,000 pounds, but the Tibetan, born and constantly residing at upwards of 14,000 feet, differs in no respect that can be attributed to diminished pressure, from the native of the level of the sea. The averaged duration of life, and the amount of food and exercise is the same; eighty years are rarely reached by either. The Tibetan too, however inured to cold and great elevations, still suffers when he crosses pa.s.ses 18,000 or 19,000 feet high, and apparently neither more nor less than I did.
Liebig remarks (in his "Animal Chemistry") that in an equal number of respirations,* [For the following note I am indebted to my friend, C.
Muller, Esq., of Patna.--
According to Sir H. Davy, a man consumes 45,504 cubic inches of oxygen in twenty-four hours, necessitating the inspiration of 147,520 cubic inches of atmospheric air.--At pressure 23 inches, and temp. 60 degrees this volume of atmospheric air (dry) would weigh 35,138?75 grains.-At pressure 30 in., temp. 80, it would weigh 43,997.63 gr.
The amount of oxygen in atmospheric air is 23.32 per cent. by weight.
The oxygen, then, in 147,520 cubic inches of dry air, at pressure 23 in., temp. 80 degrees, weighs 8,194.35 gr.; and at pressure 30 in., temp. 80 degrees, it weighs 10,260.25 gr.
Hence the absolute quant.i.ty of oxygen in a given volume of atmospheric air, when the pressure is 23 in., and the temp. 60 degrees, is 20.14 per cent. less than when the pressure is 30 in. and the temp. 80 degrees.
When the air at pressure 23 in:, temp. 60 degrees, is saturated with moisture, the proportion of dry air and aqueous vapour in 100 cubic inches is as follows:-- Dry air 97.173 Vapour 2.827
At pressure 30 in., temp. 80 degrees, the proportions are:-- Dry air 96.133 Vapour 3.867
The effect of aqueous vapour in the air on the amount of oxygen available for consumption, is very trifling; and it must not be forgotten that aqueous vapour supplies oxygen to the system as well as atmospheric air.] we consume a larger amount of oxygen at the level of the sea than on a mountain; and it can be shown that under ordinary circ.u.mstances at Dorjiling, 20.14 per cent. less is inhaled than on the plains of India. Yet the chest cannot expand so as to inspire more at once, nor is the respiration appreciably quickened; by either of which means nature would be enabled to make up the deficiency. It is true that it is difficult to count one"s own respirations, but the average is considered in a healthy man to be eighteen in a minute; in my own case it is sixteen, an acceleration of which by three or four could not have been overlooked, in the repeated trials I made at Dorjiling, and still less the eight additional inhalations required at 15,000 feet to make up for the deficiency of oxygen in the air of that elevation.
It has long been surmised that an alpine vegetation may owe some of its peculiarities to the diminished atmospheric pressure; and that the latter being a condition which the gardener cannot supply, he can never successfully cultivate such plants in general. I know of no foundation for this hypothesis; many plants, natives of the level of the sea in other parts of the world, and some even of the hot plains of Bengal, ascend to 12,000 and even 15,000 feet on the Himalaya, unaffected by the diminished pressure. Any number of species from low countries may be cultivated, and some have been for ages, at 10,000 to 14,000 feet without change. It is the same with the lower animals; innumerable instances may with ease be adduced of pressure alone inducing no appreciable change, whilst there is absence of proof to the contrary. The phenomena that accompany diminished pressure are the real obstacles to the cultivation of alpine plants, of which cold and the excessive climate are perhaps the most formidable.
Plants that grow in localities marked by sudden extremes of heat and cold, are always very variable in stature, habit, and foliage. In a state of nature we say the plants "accommodate themselves" to these changes, and so they do within certain limits; but for one that survives of all the seeds that germinate in these inhospitable localities, thousands die. In our gardens we can neither imitate the conditions of an alpine climate, nor offer others suited to the plants of such climates.
The mean height of the barometer at Mr. Hodgson"s was 23.010, but varied 0.161 between July, when it was lowest, and October, when it was highest; following the monthly rise and fall of Calcutta as to period, but not as to amount (or amplitude); for the mercury at Calcutta stands in July upwards of half an inch (0.555 Prinsep) lower than it does in December.
The diurnal tide of atmosphere is as constant as to the time of its ebb and flow at Dorjiling as at Calcutta; and a number of very careful observations (made with special reference to this object) between the level of the plains of India, and 17,000 feet, would indicate that there is no very material deviation from this at any elevation in Sikkim. These times are very nearly 9.50 a.m. and about 10 p.m. for the maxima, the 9.50 a.m. very constantly, and the 10 p.m. with more uncertainty; and 4 a.m. and 4 p.m. for the minima, the afternoon ebb being most true to its time, except during the rains.
At 9.50 a.m. the barometer is at its highest, and falls till 4 p.m., when it stands on the average of the year 0.074 of an inch lower; during the same period the Calcutta fall is upwards of one-tenth of an inch (0.121 Prinsep).
It has been proved that at considerable elevations in Europe, the hours of periodic ebb and flow differ materially from those which prevail at the level of the sea; but this is certainly not the case in the Sikkim Himalaya.
The amplitude decreases in amount from 0.100 at the foot of the hills, to 0.074 at 7,000 feet; and the mean of 132 selected unexceptionable observations, taken at nine stations between 8000 and 15,500 feet, at 9.50 a.m. and 4 p.m., gives an average fall of 0.056 of an inch; a result which is confirmed by interpolation from numerous horary observations at these and many other elevations, where I could observe at the critical hours.
That the Calcutta amplitude is not exceptionally great, is shewn by the register kept at different places in the Gangetic valley and plains of India, between Saharunpore and the Bay of Bengal. I have seen apparently trustworthy records of seven* [Calcutta, Berampore, Benares, Nagpore, Moozufferpore, Delhi, and Saharunpore.] such, and find that in all it amounts to between 0.084 and 0.120 inch, the mean of the whole being 0.101 of an inch.
The amplitude is greatest (0.088) in the spring months (March, April, and May), both at Dorjiling and Calcutta: it is least at both in June and July, (0.027 at Dorjiling), and rises again in autumn (to .082 in September).
The horary oscillations also are as remarkably uniform at all elevations, as the period of ebb and flow: the mercury falls slowly from 9.50 a.m. (when it is at its highest) till noon, then rapidly till 3 p.m., and slowly again till 4 p.m.; after which there is little change until sunset; it rises rapidly between 7 and 9 p.m., and a little more till 10 p.m.; thence till 4 a.m. the fall is inconsiderable, and the great rise occurs between 7 and 9 a.m.
It is well known that these fluctuations of the barometer are due to the expansion and contraction by heat and moisture of the column of atmosphere that presses on the mercury, in the cistern of the instrument: were the air dry, the effect would be a single rise and fall;* [This law, for which we are indebted to Professor Dove, has been clearly explained by Colonel Sabine in the appendix to his translation of Humboldt"s "Cosmos," vol. i. p. 457.] the barometer would stand highest at the hottest of the twenty-four hours, and lowest at the coldest; and such is the case in arid continental regions which are perennially dry. That such would also be the case at Calcutta and throughout the Himalaya of Sikkim, is theoretically self-evident, and proved by my horary observations taken during the rainy months of 1848. An inspection of these at the end of this section (where a column contains the pressure of dry air) shows but one maximum of pressure, which occurs at the coldest time of the twenty-four hours (early in the morning), and one minimum in the afternoon. In the table of mean temperatures of the months, also appended to this section, will also be found a column allowing the pressure of dry air, whence it will be seen that there is but one maximum of the pressure of dry air, occurring at the coldest season in December, and one minimum, in July. The effect of the vapour is the same on the annual as upon the diurnal march of the pressure, producing a double maximum and minimum in the year in one case, and in the twenty-four hours in the other.
I append a meteorological register of the separate months, but at the same time must remind the reader that it does not pretend to strict accuracy. It is founded upon observations made at Dorjiling by Dr.
Chapman in the year 1837, for pressure temperature and wet-bulb only; the other data and some modifications of the above are supplied from observations of my own. Those for terrestrial and nocturnal radiation are accurate as far as they go, that is to say, they are absolute temperatures taken by myself, which may, I believe, be recorded in any year, but much higher are no doubt often to be obtained.
The dew-points and saturations are generally calculated from the mean of two day observations (10 a.m. and 4 p.m.) of the wet-bulb thermometer, together with the minimum, or are taken from observations of Daniell"s hygrometer; and as I find the mean of the temperature of 10 a.m., 4 p.m., and the minimum, to coincide within a few tenths with the mean temperature of the whole day, I a.s.sume that the mean of the wet-bulb observations of the same hours will give a near approach to that of the twenty-four hours. The climate of Dorjiling station has been in some degree altered by extensive clearances of forest, which render it more variable, more exposed to night frosts and strong sun-heat, and to drought, the drying up of small streams being one direct consequence. My own observations were taken at Mr. Hodgson"s house, elevated 7,430 feet, the position of which I have indicated at the commencement of this section, where the differences of climate due to local causes are sufficiently indicated to show that in no two spots could similar meteorological results be obtained. At Mr. Hodgson"s, for instance, the uniformity of temperature and humidity is infinitely more remarkable than at Dr.
Chapman"s, possibly from my guarding more effectually against radiation, and from the greater forests about Mr. Hodgson"s house.
I have not, however, ventured to interfere with the temperature columns on this account.
DORJILING METEOROLOGICAL REGISTER.
Jan. Feb. Mar. Apr. May June Pressure of Atmosphere* 23.307 .305 .307 .280 .259 .207 Range of Pressure .072 .061 .083 .085 .088 .067 Mean Shade 40.0 42.1 50.7 55.9 57.6 61.2 Max. Shade 56.0 57.0 66.5 68.5 69.0 71.0 Max. Sun 119.0 124.0 120.0 125.0 125.0 126.2 Greatest Diff. 72.0 78.0 60.0 66.0 65.0 62.2 Mean Max. Shade 47.2 50.0 58.4 63.7 65.3 66.7 Minim. Shade 29.0 25.5 37.0 38.0 38.0 51.5 Minim. Rad. 16.0 23.0 27.8 33.0 40.0 47.0 Greatest Diff. 12.7 15.3 8.7 16.0 10.0 4.8 Mean Minim. Shade 32.8 34.2 43.1 48.1 50.0 55.8 Mean Daily Range of Temp. 14.4 15.8 15.3 15.6 15.3 10.9 Sunk Therm. 46.0 48.0 50.0 58.0 61.0 62.0 Mean Dew-Point 34.3 37.2 45.8 49.8 54.4 59.5 Mean Dryness 5.1 3.9 5.8 6.6 2.7 2.0 Force of Vapour .216 .239 .323 .371 .434 .515 Pressure of Dry Air 23.091 .066 .084 22.909 .825 .692 Mean Saturation .84 .87 .82 .80 .91 .93 Rain in Inches 1.72 0.92 1.12 2.52 9.25 26.96
July Aug. Sep. Oct. Nov. Dec. Mean Pressure of Atmosphere* 23.203 .230 .300 .372 .330 .365 23.289 Range of Pressure .062 .070 .082 .075 .078 .062 .074 Mean Shade 61.4 61.7 59.9 58.0 50.0 43.0 53.5 Max. Shade 69.5 70.0 70.0 68.0 63.0 56.0 65.4 Max. Sun 130.0 133.0 142.0 133.0 123.0 108.0 125.7 Greatest Diff. 62.0 62.0 70.0 65.0 68.0 77.2 67.3 Mean Max. Shade 65.5 66.1 64.7 66.5 56.5 51.6 60.2 Minim. Shade 56.0 54.5 51.5 43.5 38.0 32.5 41.3 Minim. Rad. 52.0 50.0 47.5 32.0 30.0 26.0 35.4 Greatest Diff. 3.5 3.5 10.0 12.0 12.0 10.0 9.9 Mean Minim. Shade 57.3 57.4 55.2 49.5 43.5 34.9 46.8 Mean Daily Range of Temp. 8.2 8.7 9.5 17.0 13.0 16.7 13.4 Sunk Therm. 62.2 62.0 61.0 60.0 55.0 49.0 56.2 Mean Dew-Point 60.7 60.4 58.5 52.5 46.5 31.8 49.4 Mean Dryness 0.8 1.1 1.4 4.2 3.2 10.6 4.0 Force of Vapour .535 .530 .498 .407 .331 .198 .383 Pressure of Dry Air 22.668 .700 .802 .865 .999 23.165 22.906 Mean Saturation .97 .96 .95 .86 .90 .69 .88 Rain in Inches 25.34 29.45 15.76 8.66 0.11 0.45 Sum 122.26
*These are taken from Dr. Chapman"s Table; and present a greater annual range (=0.169) than my observations in 1848-9, taken at Mr.
Hodgson"s, which is higher than Dr. Chapman"s; or Mr. Muller"s, which is a little lower, and very near.
_Horary Observations at Jillapahar, Dorjiling, Alt. 7,430 feet._
JULY, 1848
No. of Observations 7 23 27 22 20 26 12 11 25 Hour 1 a.m. 8 9 10 11 Noon 1 p.m. 2 3 Barom.
corrected 22.877 .882 .884 +.899 .899 .884 .876 .866 .852 Temp. Air 59.6 62.1 62.6 63.5 64.1 65.0 64.1 64.4 64.8 D.P. 58.9 60.6 61.3 61.7 62.3 63.1 61.7 61.0 62.6 Diff. 0.7 1.5 1.3 1.8 1.8 1.9 2.4 3.4 2.2 Tens. of Vapour .504 .534 .546 .554 .565 .580 .566 .541 .571 Weight of Vapour 5.65 6.03 6.10 6.12 6.27 6.44 6.13 6.00 6.32 Humidity .988 .950 .960 .945 .945 .940 .923 .892 .930 Press. of Dry Air 22.373 .348 .338 .345 .334 .304 .310 .325 .281
No. of Observations 23 13 10 6 6 22 6 6 19 Hour 4 p.m. 5 6 7 8 9 10 11 M.n.
Barom.
corrected 22.846-.840 .845 .853 .867 .878 .885 +.887 .887 Temp. Air 64.1 64.7 63.7 62.7 61.0 60.7 60.5 60.2 59.8 D.P. 61.7 64.0 61.5 61.1 59.5 59.4 59.5 59.2 59.1 Diff. 2.4 0.7 2.2 1.6 1.5 1.3 1.0 1.0 0.7 Tens. of Vapour .554 .597 .549 .542 .515 .512 .514 .508 .507 Weight of Vapour 6.13 6.62 6.12 6.03 5.74 5.72 5.75 5.70 5.68 Humidity .924 .978 .928 .948 .952 .960 .968 .965 .975 Press. of Dry Air 22.292-.243 .296 .311 .352 .366 .371 .379 +.382