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Paul Parey, of Berlin, under the title of "Landwirtschaft in
England."

THE current number of Wundt's Philosophische Studien icon-
tains two experimental articles—both dealing with problems of
psychological optics. The first (A. Kirschmann, "Beitraege
zur Kenntniss der Farbenblindheit ") gives an account of a
number of interesting cases of colour-blindness, together with
criticisms of existing theories. A unique case is that of an
inherited, unilateral (left) blindness to the qualities violet, green
and yellow. In the second (E. B. Tutchener, Ueber
binoculare Wirkungen monocularer Reize ") an attempt is made
to show that stimulation of one retina is followed by an excita-
tion-process in the other. The psychophysical results are
supported by recent physiological discovery.

THE following are the arrangements at the Royal Institution
for the Friday evening meetings before Easter, 1893 :-Friday,
January 20, Prof.
Dewar, F.R.S., liquid atmospheric
air; Friday, January 27, Francis Galton, F.R.S., the just-
perceptible difference; Friday, February 3, Alexander Siemens
theory and practice in electrical science (with experimental
illustrations); Friday, February 10, Prof. Charles Stewart,
some associated organisms; Friday, February 17, Prof. A. H.
Church, F.R.S., turacin, a remarkable animal pigment con-
taining copper; Friday, February 24, Edward Hopkinson,
electrical railways; Friday, March 3, George Simonds, sculpture
considered apart from archæology; Friday, March 10, Sir
Herbert Maxwell, early myth and late romance; and Friday,
March 17, William James Russell, F.R.S., ancient Egyptian
pigments. On Friday, March 24, a discourse will be delivered
by Lord Rayleigh. On March 31 and April 7 (the Fridays in
Passion and Easter Weeks) there will be no evening meetings.

THE following are the arrangements for lectures at the Royal
Victoria Hall in January :-January 3, Mr. Charles E. Reade
on a trip through India, with anecdotes of the mutiny;
January 10, Mr. A. Hilliard Atteridge on some old Belgian
towns; January 17, Prof. Carlton Lambert on the romance of
the stars; January 24, Dr. Dallinger on spiders, their work
and their wisdom.

THE fermentative changes which the leaves of the tobacco plant are made to undergo before they are worked up and finally handed over to the public, are of the greatest importance in determining the quality of any particular tobacco. It was formerly supposed that the alteration in its condition thus brought about was due to purely chemical changes induced by the process of "sweating" which the leaf undergoes, but some interesting experiments made recently go to show that these important results are effected by special micro-organisms. In a paper read before the German Botanical Society, Suchsland gives an account of some investigations which he has been con. ducting on the bacteria found in different kinds of tobacco. He has examined fermented tobacco from all parts of the world, and found large numbers of micro-organisms, although but few varieties, mostly only two or three different species in any particular brand and but rarely micrococcus forms. But what is of especial interest is the discovery that pure cultures of bacteria obtained from one kind of tobacco and inoculated on to another kind, generated in the latter a taste and aroma recalling the taste and aroma of the original tobacco from which the pure cultures had been in the first instance procured. Thus it may be possible in the future to raise the quality of German tobacco, not, as heretofore, so much by careful culture and judicious selection of varieties, which has so far proved unsuccessful, but by inoculating pure cultures of bacteria found in some of the fine foreign tobaccos on to our own raw material, whereby similar fermentative changes may be induced

and the quality correspondingly improved. The furth
promised by Suchsland will be looked for with much
In connection with the above experiments on the "tra
tion," so to speak, of micro-organisms, it is interestin
some results obtained lately by Nathan (Die Beden x
Hefenreinzucht für die Obstweinbereitung). The a
alcohol present in such wines as cider, currant win el
generally from 3 to 4 per cent. This small proportion í 72
in part due to the necessarily large dilution of the
water, which considerably reduces the nitrogenous co
of the "mu-t," and also to the fact that the yeast,
to Hansen mostly present on sweet fruits is the Sacr
apiculatus, which only possesses a feeble fermenian te
Experiments were made to see whether, by incre
nitrogenous constituents of the “must,” and introduc
cultivation of a vigorous wine-yeast, the yield of aler
be greater. It was found that by adding a small
nitrogenous material, such as o'15 gram. ammonium
and 5 cubic centimetres of wine-yeast per litre to th
must" (which was the fruit selected) 2 per cent. mo
was obtained, and not only was this the case, but
possessed a finer and more vinous taste than that un
which had only received an additional supply of i s=
chloride without the wine-yeast. Kosutany in a pape 1-
in the Landw. Versuchsstationen, 1892, has reta
results of his invest gations on the behaviour of cer
of wine-yeast. He states that not only is the pe
alcohol yielded very different with particular yeas
also the taste, smell, and bouquet of the wine OCI
special cultures were distinctly different according :-
of yeast employed. It is hoped that, as in the case
so with wine, it may be possible to raise the ças.
judicious transplanting of bacteria obtained from in

THE additions to the Zoological Society's Gard
the past week include a Squirrel Sci
China, presented by Mr. Julius Neumann ; a Craw :
Eagle (Spizactus coronatus) from South An
Mr. T. H. Mills; a Macaque Monkey (May 1
from India, deposited; three Sulphury Tyres
Sulphuratus) from South America, six commen
(Mareca penelope, 38, 39), four common Pint
28, 29), two Pintailed Sand Grouse (Pirace &
European, purchased.

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1 8 50 IE MARKINGS ON MARS.-In No. 25 of the Publications e Astronomical Society of the Pacific, Mr. Schaeberle has a minary note on the question as to whether the darker and brighter areas on Mars are water and land or vice versa. ng observed the planet from June 11 up to the present time as been led to the conclusion opposite to that of SchiapaFlammarion, and other observers, and considers that after e dark portions should be considered as land and the bright ater. In raising such a question as this Mr. Schaeberle een very reserved, for should his opinion receive due attenas of course it should do, and be corroborated, the planet's ce will be looked upon in quite a different light than for In this note he sets forth a few of his reasons for coming ch a conclusion, and it may interest many of our readers if ate some of them briefly. If the dark marking- be taken ad, would not the irregular gradations of shade be more ally expected than if we consider them as fixed surface es? "Light reflected from a spherical surface of water ight state of agitation would vary uniformly in intensity. position, the centre of the planet would, for a water sur#ppear brightest. Observations show that within a certain ce from the edge of Mars there is a gradual increase in ady lustre of the brighter areas towards the centre of the Assuming these dark areas to be water, then they thus be least dark near the centre, which is somewhat y to observation. With reference to the "canals," he at they on this hypothesis "correspond to the ridges of ins which are almost wholly immersed in water," while gard to their observed doubling he remarks that they can ained as "representing parallel ridges of which our own nishes examples." As a concluding argument he takes ved terrestrial observation, the view of the lower end of ncisco Bay from Mount Hamilton, San Francisco being es away. At all hours of the day, he says, "the of San Francisco Bay (as seen from the top of Mount n) is much brighter than the neighbouring valley and s at the same distance." He further adds that the line makes an angle of more than 87° with the normal to the the bay, while the observer's po-ition "varies all the being nearly in a direct line between the bay and the e position in which the sun is nearly in the direction of

ICK

OBSERVATORY.-Miss Milicent W. Shinn is the a very interesting pamphlet on the history of the Lick ical Department of the University of California. In pages she brings together much with regard to the Es connected with the founding of the giant refractor -t generally known. For instance, it is curious to Mr. Lick wished to be immortalized by leaving er costly statues of himself and his family, and when such statues would be preserved for all time, was by Mr. Staples that "more likely we shall get into a Cussia or somebody, and they will come round here

the city." Mr. Lick was so struck by this, that he asked, "What shall I do with the money, then?" How this question was answered is now well known, and astronomical science was presented with the finest object-glass that was ever made.

Mr. Lick's deed prescribed that the Observatory should be "made useful in promoting science," and up to the present these words have been carried out to the letter. The big

telescope has not been preserved for one side of astronomical science, but has dived into all branches, as every astronomer is aware Not only have minute double stars been observed and measured, but the spectroscope has been employed, from which excellent results have been published, while lunar photographs, equalling, if not excelling, those that had been previously obtained have brought to light much to set us thinking about. Jupiter's fifth moon is perhaps the latest arrival of which we have heard, and this, following just 300 years after Galileo's discovery, would alone render the Observatory famous. That the Lick Astronomical Department, during the few years of its existence, has done an immense amount of good work, especially when one takes into account the comparatively small staff on hand, cannot be denied, and we hope the day will come when the number of such telescopes will be increased, for the everopening fields of research point out how necessary they are.

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WASHINGTON MAGNETIC OBSERVATIONS. The United States Naval Observatory has quite recently published their magnetic observations that were made during the past year, prepared on the same plan as that for 1889-90. The observations for 1891, as Mr. Hoogewerff (who was in charge for the greater part of the year) informs us, are better than those of former years, owing to the fact that the reductions took place at no very distant dates from the observations, the experience thus gained helping to correct and guard against conditions which might have tended to give rise to errors. The introduction contains a description of the buildings, methods of observing, together with the personnel during the year, concluding with a description of the tabular results. The tabular results, as usual, show the mean hourly readings for the elements for each month, Table I. containing the mean values for the four years 1888-91.

Simultaneous with this volume was also issued the meteorological observations and results for the year 1888.

GEOGRAPHICAL NOTES.

A SPECIAL num.ber of the Mouvement Géographique is devoted to a series of important despatches from M. Alexandre Delcommune, chief of the Lomami expedition of the Katanga Company. Entering the Lomami from the Congo, the party left the river on May 13, 1891, and explored the entirely untraversed territory between its upper valley river and that of the Sankuru as far as 8° S. Thence they turned eastward and reached Lake Kassali on the Lualaba, and struck south through Garenganze's country to Bunkeia. Making a circuit through Katanga and westward, they found the Lualaba near its source, and following it for 200 kilometres, discovered a grand gorge at Nzole, where the river flowed in a succession of wild cataracts between cliffs nearly a thousand feet high, and not more than forty yards apart. From the rapids they returned to Bunkeia, travelled north-eastward over the plateau, cro-sing the Luapula at its outflow from Lake Moero, and ultimately reached Lake Tanganyika. The difficulties overcome were very great, and the sufferings of the caravan have rarely been surpassed even in the grimmest records of African travel.

AMONGST the English travellers who have recently arrived in London are Mr. Selous, the famous South African hunter, and Mr. Conway, who has probably climbed higher than any other European in the Karakoram range. Both gentlemen will read papers to the Royal Geographical Society early next year

THE arrangements for the Royal Geographical Society's evening meetings after Christmas are unusually varied. Mr. Hose will describe his journey up the Burram river in Sarawak to Mount Dulit, at the first meeting in January. The second meeting will be devoted to the Island of Yezo, when Prof. Milne and Mr. Savage Landor will read papers. Papers by Captain Bower and the American traveller, Mr. Rockhill, on Tibet, will be given later; and Lieutenant Peary will personally describe

his experiences in the north of Greenland. In March Prof. Bonny will lecture on the action of ice in producing geogra phical forms, and there will be other papers dealing with the scientific basis of geography.

THE death of Cardinal Lavigerie on November 24 removed one of the most powerful personages who have recently influ enced the geography of Africa. It is very largely on account of his labours that the French Roman Catholic missions have played so conspicuous a part in combating the slave trade, and to him also is due the formation of a much-needed Belgian Anti slavery Society.

THE British Government having decided to relieve the East African Company from the responsibility of occupying Uganda, an Imperial commission, under the charge of Sir Gerald Portal, will set out from Mombasa as soon as it can be got ready to take over the administration of the country. Another fact of some interest is the revival by Mr. Cecil Rhodes of the idea of exploring Africa by telegraph. He proposes to lay down a line from the Cape to Uganda, and ultimately to extend it to Egypt. In a few months the South African Company's wires will have reached the mission station of Blantyre north of the Zambesi, and there are no serious physical difficulties in continuing the line to the head-waters of the Nile. The effect on the exploration of Africa will be enormous, not the least important result being the possibility of arriving at the true longitudes of places in the interior of the continent.

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The observations were begun with the object of verifying the commonly received theory of dew, and with a strong feeling that the results obtained by Col. Badgeley, described in the Proceedings of the Royal Meteorological Society for April, 1891, opposed as they were in some measure to the accepted teaching on the subject, would not be corroborated. When, after exposing inverted glass tumblers and pans on grass and bare earth in the summer of 1891, dew was often found in surprising amount in the interior, I attributed the deposit to vaporous air which might have entered under the rim and parted with its moisture in the calm of the inclosed space. But when it was found that a tumbler pressed down into dry earth, and other vessels admitting little air from outside, were considerably be. dewed in the interior ; and when, further, similar vessels inverted on earthenware or metal plates were found to be very slightly or not at all bedewed inside, it became more probable that the vapour condensed in the interior of vessels over grass and garden earth had proceeded from the earth beneath. Next, it was found that china plates, admitting a flow of air between their lower surfaces and the ground, were more heavily bedew ed on their lower than on their upper surfaces, and that a cylinder of glass was most bédewed on the lower outer and upper inner surfaces. These observations confirmed the suspicion that the dew on the inside of the hollow vessels was derived from the ground. It was for a long time a matter of doubt and difficulty that vessels inver ed over dry, dusty earth and dry turf were found copiously bedewed within on the morning following exposure. On many mornings the amount of dew in the interior increased in some proportion to the precautions taken to exclude free air, and it seemed highly improbable that moist air penetrated, without depositing on its way much of its moisture, either through the dusty earth banked round the edges of the vessel, and exposed to the sky, or else through the dusty covering of earth below the vessel from lower layers.

In December, 1891, during hard frost and very fine weather, with calm or very light airs, the ground being frozen hard, leaves of bushes, ferns, &c., were seen to be frosted both on their upper and lower sides, though much less on the lower sides facing the bare ground than on the upper sides facing the open sky. Where thick fern grew between the observed leaves and the ground, there was no rime on the lower sides of the overhanging ferns or leaves. This seemed to show that the rime on the lower sides of ferns was due to exhalation from the ground, for the interruption of radiant heat from the earth by dry litter would rather favour than reduce the frosting of the under sides. Live leaves on bushes, and dead leaves on the ground, were whitened with

frost on their upper sides, and had a thin film or coat of parent ice on their lower sides. Leaves and sticks on ground were less frosted on the sides facing the ground tha the top. Thick planks between a few inches and one foota the ground were about a third as much frosted on the lower on the upper sides. Considering that the upper side of a I inch thick would fall to a considerably lower temperat radiation than the lower side, it may be supposed that the position would have been largest on the lower side if they' ben at the same temperature. That much frost came fr air independently of the ground, was shown by the whiter 12 feet above the surface of the earth. On the other han grass was much more heavily frosted. Moreover, tumblers verted and pressed down on dry, hard, bare earth, on sa on hard turf, were moderately frosted inside, besides being th frosted outside. The indications, on the whole, seene resemble those of the previous June, but the vapour c ation attributable to exhalation from the earth bore smaller proportion to the total deposit than in the case of on interior surfaces observed in summer

Boards, tiles, and stones (sandstone) in heaps were is on the top, and especially in cracks and indentations of the surface, but not in the interstices between the separate Stones on the ground were sometimes not frosted at all top, but much on the parts against the sandy earth, and bedded in the ground.

Further experiments in May and in the summer ne 1892 gave strong confirmation of the evidence that mat and frost are caused by exhalation of vapour from the eart in dry weather.

The facts that

(1) A large quantity of dew was invariably found nights in the interior of closed vessels over grass and sand (2) Very little or no dew was found in the interior of inverted over plates on the ground.

(3) More dew was found on the lower side of a square, 54 raised, china plate over grass or sand than on the lower similar plate placed upon the first.

(4) The lower sides of stones, slates, and paper on sand, were much more dewed than the upper sides I wooden back of the minimum thermometer on clear etc when lying on earth, sand, or grass was almost invariab before the upper surface.

(5) The lower side of plates of glass, I or 2 in. abor were as much or more bedewed than the upper sides. (6) Leaves of bushes, leaves lying on the ground, a of grass were about equally bedewed on both sides.

(7) The interior of closed vessels inverted on the g covered with two other inverted vessels of badly-on substance was thickly bedewed, and the grass in circular inclosures also thickly bedewed.

(8) The deposit of dew on the interior of closed vessels over dry garden earth was much less than over sa although the powdery condition of the earth in the showed that no deposit from the air had taken place face during the night.

(9) Usually a greater amount of dew was deposre interior of vessels when the earth was moist at a below the surface than when the earth was at its dries

(10) The temperature of the space under a glass other object suspended near the surface of the ground K. than that of the upper surface of the object, and, a cloudy film was produced first on the lower surface,to a proof that a large part of the dew formed is de vapour from the earth.

Moreover, the large difference often observed be quantity of dew deposited in the interior of a vesse plant, and the quantity of an empty vessel, proved dew may be derived from the earth through plants

Drinking glasses inverted over grassy turf, and over by, from which the grass was removed, showed a s of deposit on the glasses inclosing grass. Moe condensed on plates suspended over grass than over In these cases the conditions are somewhat artifer! grass, which was covered by a suspended plate or in glass, would be warmer than if the exposure to the say but the disturbance thus caused would tell as mec in favour of deposition on the interior surface. objected that the air in and above the grass wee'! owing to the radiating grass, than over the bared

1

refore more dew would be deposited from the air; but this jection would scarcely be valid where a small plant was insed on bare earth and the deposition on the interior of the ss compared with that on a glass not inclosing a plant. Recent investigations have proved the evaporation from plants be very large, and since evaporation proceeds by night as ll as by day, there can be no reason why a moderate protion of the dew deposited on the surface of blades of grass I on leaves of plants generally should not be derived from the our which they exhale. The fact that an equal quantity of v is deposited on glass, china, painted wood, &c., exposed to sky to that depo-ited on grass, may seem to minimize the dence of plant exhalation, but we must remember that the ole of the stratum of air near the ground is rendered more orous by these exhalations, and that therefore the dew point poner reached on the surface of any body exposed to the sky he midst of vegetation than on bare open ground. Moreover, thickness of the substance prevents earth heat from much cting the upper surface. The effect of grass in promoting formation is owing-(1) To its radiative power cooling its ace below the dew-point. (2) To the consequent cooling of stratum of air in and over the grass to a point much below of the air a few feet higher. (3) To the obstruction offered the grass to any light air or breeze on a nearly calm night, the consequent settling down, without much disturbance, of ld heavy stratum. (4) To the prevention by the grassy ering of the drying up process by sun and wind which takes e on bare ground, and to the moist earth which therefore ts under grass near the surface even in dry weather. (5) To exhalation of vapour from the grass.

he realization of these causes explained what was always, ious to these observations, a difficulty to me, the almost e absence of dew on heather and dry fern in the summer. 1 after heavy dews, heather was invariably found perfectly In fine, calm winter weather, with white frost, heather be a good deal whitened, and the frost is then derived ly from the open air. Wood, being a good radiator and conductor, is heavily bedewed and frosted. ones, whether of sandy composition and appearance, or of grain like flint, pebbles, and slate, are not often visibly wed or frosted on the top on clear nights. On their sur, touching or very close to the ground, they are heavily be:d and frosted. A moderate radiative power, their usual tion removed from grass and vegetation, and in the case of lose grained stones, a conductive power greater than that ives, grass, and wood, though less than that of metals, prethe deposition of much atmospheric moisture on their sed sides. But when air highly charged with vapour ims on them in a confined space, as on their lower sides, conition readily takes place, just as it will take place when any ance, even polished metal, is held above the spout of a of boiling water. It is apparent that since stones act as ensors to the vapour constantly arising from the earth, and the heat of the sun and temperature of the air by day only ly raise the temperature of the earth immediately beneath e stone, while the radiation of heat from the stone and low mperature of the night cause the lower side of the stone to y cold at night, a rather large amount of moisture must be ted on its lower surface in every twenty-four hours, and the I on which it rests must in our climate remain always very The space between the stone and the ground consebecomes the abode of many insects which live well in nd darkness.

Isional observation of the distribution of dew, without comparison with the state of the weather, gives an imn of capriciousness which only continuous records comvarious conditions can remove.

osition is generally favoured by a humid air, and therefore country by southwesterly and westerly winds, which bring e land the vapour derived from evaporation of the Atlantic

A smaller fall of temperature by radiation brings about ation, and there is less tendency in any deposit to te than in a drier air. Radiation may produce a greater mperature in dry air, but the distance from the dewcommonly too wide to compensate greater humidity ater cooling.

Is also very favourable to dew-formation. It allows of vapour in the air to remain sufficiently long in contact 1 radiating substances to become greatly cooled, and so e condensed upon them, and it prevents the dispersion

of the stratum of air near the ground, which is continually cooling by contact and radiation. Thus dew goes on forming while the air falls lower and lower beyond its original dew point, and while by a very gentle movement an interchange is kept up between the warmer air touching the ground beneath the grass, and the cold air on the surface of the grass, and between differently cooled layers and portions of air above it. If the air is very humid, a very slight air or breeze is favourable to heavy deposition. On ordinary clear nights, calm and light airs allow the reduction of the lowest stra'um of air to the dew-point, and there is no liability to evaporation of the minute deposited particles by portions of air above the dew-point being driven against them. When the air is rather dry, as often happens at night in dry summer weather, and in winter frosts, calm is frequently a necessary condition for the deposit and appearance of dew and white frost. The deposit may be observed to take place on the cessation of wind, and again, the change from calm to wind soon dries off the dew which has already formed. On other occasions, when there is a gentle air or breeze, dew and frost are deposited only in sheltered places, as on the most sheltered slopes of fields, on banks sloping to leeward, on leaves on the lee side of bushes and trees, on the lee side of mole-hills, posts, railings, and other objects. Hollows, depressions, and cracks, in paper, glass, stones, tiles, wood, and leaves, are more bedewed than flat surfaces from the same reason,-the reduction below the dewpoint of air less diluted than that which is more free by currents of higher temperature and greater dryness. With a fresh west wind in a clear night, the raised and ribbed parts of leaves, &c., may be thickly bedewed and frosted, but the hollows and folds scarcely if at all less, and the sides of buds, thorns, &c., are more frosted than the points. The wind is, in fact, often sufficiently removed from the dew-point to prevent deposition or continuance of moisture on all parts which are fully exposed to it. Not even free radiation to a clear sky then avails to plant frost-growths upon the object whose temperature is being perpetually supplied by the forcible impact of warmer air.

Free radiation or exposed situation is, on the whole, perhaps the most effectual cause of dew on very many nights in the year. In a level country those parts of a field which are least sheltered by trees and hedges gather most dew and frost on calm nights. Similarly, those parts of any flat substance, such as a sheet of glass or paper, which have the most uninterrupted exposure to the sky are most bedewed. The tops of bushes, posts, railings, inverted drinking glasses, pans, &c., are on calm nights, and sometimes breezy nights, more bedewed than the sides. Greater cold by greater radiation in these cases produces greater deposition from the cooled air which comes in contact with the freely radiating surfaces. It must be remarked, however, that radiation from fine points, such as the tips of sharp thorns, is often not sufficient to counteract in air which is not very humid the effect of the continual impact of air above the dew-point and higher in temperature. Close to the ground the case is different, for there the temperature of the low stratum of air is lower, and usually about the dew-point, there is little movement, and vapour from the ground increases humidity; but even in this situation the points of grasses, &c., are often less bedewed than the sides.

That free radiation is by no means necessary for the formation of heavy dew on grass is proved by the experiments detailed above, made during the summer of 1892. The grass was found heavily bedewed in dry weather within three enclosures of earthenware by which radiation was arrested.

Since grass covered by hollow vessels, and the interior of hollow vessels themselves, are thickly covered with dew, it would seem likely that the grass under overhanging trees would be as thickly bedewed as the exposed grass in a field, and that the under sides of the overhanging leaves would also be wetted. This is not the case. And there are differences in the two situations sufficient to account for the absence of dew under leafy trees. In the first place, on a calm night, the air under a tree is warmer than in the open owing to radiation from the ground being arrested. Secondly, whatever vapour escapes from the earth is unable to condense on the grass which covers it, the grass being but little colder than the air and vapour. Thirdly, and herein lies the chief difference, the air under the tree moves freely and is above the dew-point, since the earth and other objects which it touches are warmer than the grass and air outside. If the air were confined in a small space, the increments of vapour issuing from the earth, and the gradual cooling of the grass under the tree and of the tree itself, might cause deposition, but air which has parted with much of its moisture outside is

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constantly mixing with a considerable body of air already warmed under the sheltering canopy. Thus all objects under the tree remain above or not much below the dew-point of the air which touches them. Yet, on a calin night, long grass and other substances a little raised above the ground are sometimes heavily bedewed, though largely hindered by overhanging branches from losing their heat by radiation. They often remain nearly dry till the morning hours, and then reach a temperature below the dew-point. The absence of dew under trees and bushes is, within limits, roughly proportional to the area of ground covered. large surface of dry ground slowly parting with its heat during the night has a powerful effect in preventing condensation. Small bushes on a humid clear night are often much bedewed even on their lower leaves. On the night of October 5, 1892, both sides of the leaves of bushes in all sheltered situations were found thickly bedewed, but where leaves were either exposed to the slight breeze which was blowing, or near the wall of the house on which the sun had shone, they were dry. The warm, dry wall of a house acts a part similar to that of the earth under a tree in radiating warmth to neighbouring objects, and in warming the air by contact. The vapour emerging from earth sheltered by foliage several feet above it has time to mix well with air before coming in contact with solid objects. In the hollow vessels, and even in the space between a raised plate of glass and the earth, the vapour which rises from the earth has no time to become equally distributed in the air before meeting with substances colder than itself; in the closed vessels the initial amount of vapour is augmented so as to produce constant saturation. Objects, such as drinking glasses, raised several feet above the grass, were seldom much beaewed, and often quite dry.

The increase of pasture-land in England must have a considerable effect in increasing cold by radiation, and in diminishing the amount of vapour in the air at night by deposition on grass. The sensible moisture at night must be increased near the ground, the dew-point being quickly reached on a clear night over grass.

The large quantity of dew found on plates and other objects over sandy ground, dry to a depth of several inches, proves the possibility of a large emanation of noxious vapours from soil containing decaying organic matter below a covering of sand. The ague of parts of East Anglia and of sandy malarious districts may be thus accounted for.

Houses built on sandy ground over a damp subsoil may be considered as scarcely more wholesome than if built on the damp soil itself.

In late summer and early autumn the high temperature of the soil in comparison with the temperature of the surface and of the air near the ground at night, must have a powerful effect in the production of vaporous exhalations. The heavy rains which so often occur in October, the wettest month of the year, must cooperate with a falling air-temperature in driving out air from the pores of the earth.

In nearly all the conclusions of Wells, as stated in his admirable Essay on Dew," my observations lead me to concur. He found that calm is favourable to the precipitation of dew; that if, in the course of the night, the weather, from being calm and serene, became windy and cloudy, not only did dew cease to form, but that which had formed either di-appeared or diminished considerably; that if the clouds were high and the weather calm, dew sometimes formed to no very inconsiderable extent; that dew often forms on shaded grass even several hours before sunset, and continues to form after sunrise; that, if the weather be favourable, more dew forms a little before, and, in shaded places, a little after sunrise, than at any other time; that on substances elevated a few feet above the ground it forms much later in the evening, but continues to form as long after the rising of the sun as upon the ground; that dew is more abundant shortly after rain than during a long tract of dry weather; that dew is always very copious on those clear and calm nights which are followed by misty or foggy mornings, and also on clear mornings after cloudy nights, and generally after hot days; that more dew was formed between midnight and sunrise than between sunset and midnight, owing doubtless "to the cold of the atmosphere being greater in the latter than in the prior part of the night;" that whatever diminishes the view of the sky diminishes the quantity of dew; that a substance placed on a raised board of some extent acquired more dew on a very stili night than a similar substance lying on grass; that bright metals attract dew much less powerfully than other bodies, that a metal which has been purposely moistened will often become dry

though similarly exposed with bodies which are attracting and that wool laid upon a metal acquires much less dew the equal quantity laid upon grass in the immediate vicinity; the metal plate on grass always became moist on the lower during the night, though the upper side was often very dry, that if the plate was elevated several feet in the air, the co of both sides was always the same, whether dry or moist wool on a raised board was commonly colder than on the go! on very still nights, and that the leeward side of the board colder than the windward; that bare gravel and garden were very much warmer after sunset than neighbouring gu that on dewy nights the temperature of the earth half an ins an inch beneath its surface was much warmer than the grass it, and than the air; that metal covering grass was only sig colder than the grass covered, and this again colder than earth; that metal thus exposed was warmer than air 4 feet: it, and much warmer than neighbouring grass; that the in the quantities of dew, formed upon bodies of the same in different situations, was occasioned by the diversity of perature existing among them; and that on nights favour the production of dew, only a very small part of what occ owing to vapour rising from the earth.

The last of these conclusions Wells supported by the vation that the dew on the grass increased con-iderably sunset, the same time at wh ch dew began to show itself? raised board, and by the reflection that, "though boules on the ground after they have been made sufficiently c radiation to condense the vapour of the atmosphere will be to retain the moisture which they acquire by conde. vapour of the earth; yet, before this happens, the rising must have been greatly diminished by the surface of the ga having become much colder." He adduced the fact substances on the raised board attracted rather more throughout the night than substances lying on the grass admitted that all the dew on calm, cloudy nights might tributed to condensation of the earth's vapour, since nights the raised board was dry.

But if the grass was moist on these calm, cloudy nigh the moisture were owing to earth-vapour, it is only rea to infer that a very much larger quantity was owing to vapour on clear nights when radiation was comparative Moreover, the fact that substances on the raised board ber wetter than substances on the grass may be attributed t non-conducting wood intercepting the warmth radiated ground, and thus allowing a substance on the upper s the board to become colder than a substance on the grass, with regard to the "rising vapour " being greatly dia the surface of the ground having become colder, il e appear that such diminution actually occurs, owing pos the influence of the high temperature of the preceding day ing the moist earth at a little depth below the surface a same time. I have found the dep sition of earth-vapour ceed at a rapid rate after sunrise over grass.

Wells explains with much ingenuity the reason why trees often remain dry throughout the night, while these are covered with dew. But he does not, I think sufficient weight to the fact which he mentions amo that the air near the ground is near one of its sources of while the tops of trees are removed from that source is both damper and colder near the ground; a stratum air rests upon warm earth emitting vapour. The t are pervaded by air which is drier and warmer, and the do not allow air to rest long enough on their cooled s part with sufficient heat in order that condensation may

I have found that when the air is clear and not hum tion into space is often not sufficient to cause visible ces except in sheltered calm places, and in the same c air deposition takes place more on broad surfaces tha shoots, threads, and points, and more on the face, tha edges of leaves. It appears necessary that a certain sta temperature below that of the air, and a certain protec re-absorption by the drier portions of air which pass be attained in order that dew and frost may accumu on the other hand, the air is very moist, with a te mist or fog, a very large condensation takes place objects, and especially on those which are at some the ground, such as the branches and twigs of treethorns, spiders' webs, and other thin filaments are det bedewed. Mist or fog often follows.

When some mist has formed on such a night, the..

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