November 16, 1882. ] JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 447 
are plunged should be renewed every autumn, but care should be 
exercised that the bottom heat does not exceed 70° ; therefore 
leaves only should be used, and these not in any great bulk. A 
minimum winter temperature of 60° is necessary to keep the plants 
in robust health.—W. L. H. 
THE FORMATION OF DEW. 
In his laudable endeavour to set me right in the matter of dew- 
formation “ W. Y.” has confused two distinct phases of the sub¬ 
ject. He rightly says that “ the cause of the deposit is an inter¬ 
esting one,” and when I tell him that my whole theory and 
practice of giving air, which is a somewhat elaborate one, is 
entirely based on what I have stated about dew-formation he will 
readily acknowledge that I am quite alive to its importance. If 
he succeeds in proving me wrong in this part of the subject my 
whole treatise stands condemned, but I hope I shall be able to 
show that what I have stated is tolerably correct. 
“W. Y.” says, correctly enough, “that hot air can hold more 
moisture invisible than cold air, and that as the cooling process 
goes on the air becomes saturated— i.e., can hold no more invisible 
moisture, but must deposit it or make it apparent in the form of 
fog, &c.” This agrees with a text-book I have by Professor 
Ansted, where minute particulars and calculations are given thus : 
“ It is found that when the temperature is 50° each cubic yard of 
dry air (about 168 gallons) can hold nearly 150 grains (one-third 
part of a fluid ounce) of water. At 32°, or the freezing point of 
water, only one-half this quantity is contained, and at 70° nearly 
double can be absorbed and retained in an invisible form. 
When a change of temperature occurs, and the alteration is in the 
direction of increased heat, the air continues to absorb ; but the 
moment that a diminution of heat takes place, owing to any 
cause, not only does the power to absorb cease, but the power to 
retain is lost, and visible vapour represents the difference.” 
So far, then, Professor Ansted, “ W. Y.,” and my humble self 
are in perfect accord ; but when “ W. Y.” comes to apply the 
theory to the dew-formation in my fiuit houses he is not on such 
safe ground. He says “ It is not the rise of temperature caused 
by the sun coming out which causes the dew to deposit on the 
Vines, slates, &c., because any rise of temperature must infallibly 
cause an increase in the moisture-carrying capacity of the air 
before it can cause much moisture to be evaporated from the 
ground in the house or anything in the house ; but it is the radi¬ 
ating power of the plants and other substances which have, so to 
speak, chilled themselves, and thus previously caused the air to 
deposit dew on them.” 
Now a dew-deposit in any way is one of the things we have to 
guard against, and we do not generally allow our fruit houses to 
fall rapidly to a sufficiently low temperature to cause dew-forma¬ 
tion in this way ; and practically in well-managed forcing houses, 
unless in the earlier stages of growth, before the fruit is far 
advanced, no dew-deposit takes place from a decreasing tempera¬ 
ture. Like the outside temperature, that of our houses keeps 
declining generally till sunrise, when it reaches the lowest point; 
but it does not decrease so rapidly as that outside, owing to the 
presence of a warming apparatus and the screen of woodwork, 
glass, and foliage, which checks radiation, so that what is generally 
called the dew point is not actually reached. In the earlier 
stages of the growth of some fruits we are not careful to prevent 
dew, and with such decorative plants as have not very soft f< diage 
we often find it to our advantage when no flowers are present to 
allow the dew to form on them. But all this is entirely at our 
command, and it is not a matter of haphazard work, as “ W. Y.” 
seems to imagine. A very little precaution will prevent its for¬ 
mation altogether, and on the other hand, the atmospheric con¬ 
ditions being favourable, dew can be created at will. 
For the purpose of my argument dew may be called distilled 
vapour. We have seen that when the temperature of what is 
called dry air is 50° there can be present in it as much as a third 
of a fluid ounce of water to the square yard, and that the tem¬ 
perature has only to rise 20° higher for the water-carrying capa¬ 
city to be doubled. Now I have repeatedly said that a moist 
atmosphere is not of itself inimical to the keeping of fruit, but 
that a dry air is so ; and in practice there is certainly no lack of 
moisture at any time in the houses under my charge, so that dew 
or no dew is merely a question of warming and ventilating. In 
distillation the vapour is condensed when it comes in contact 
with the cold surface of the refrigerator ; in our fruit houses, when 
badly managed as regards ventilation and warming, the fruit may 
too often be a refrigerator, and condensation take place on its 
surface. 
It matters not how warm the air may become, and its water¬ 
carrying capacity consequently increased, if a cold surface is 
presented to it there will certainly be condensation, just as there 
would be on a piece of cold metal held in the steam from the 
spout of a tea-kettle. 
There are, then, two distinct and separate conditions of the 
atmosphere during which dew is deposited. Firstly, when the air 
becomes suddenly cooled it can no longer hold all the moisture it 
contained in invisible suspension, and must deposit it in the form 
of dew, or it changes to fog, Ac. Secondly, when the temperature 
rises rapidly it takes up of necessity a greater quantity of mois¬ 
ture, and any surface with which it comes in contact that is suffi¬ 
ciently cold acts as a refrigerator, and vapour is condensed on it 
so long as the said surface remains cold as compared with the air 
surrounding it. Under the second conditions it will be found that 
the order of things is somewhat reversed ; for whereas under the 
first-mentioned conditions it is, as said in the book just referred 
to, the case that “ plates of metal (good conductors of heat) remain 
quite dry, while wood (a very bad conductor) becomes quite wet,” 
under the second conditions, or when the deposit takes place from 
a certain rise of temperature, the metal (the good conductor) is 
the first to become wet, and the wood, if not painted, is one of 
the last. 
Everybody must have noticed that when the weather suddenly 
changes from cold to warm that slates, stones, metal, and many 
other things become damp in proportion to the suddenness and 
extent of the change. These substances cannot be warmed so 
quickly as the surrounding air ; the moisture consequently is con¬ 
densed on them, and there it will remain till sufficient time has 
elapsed for the warm air to penetrate them. This is just what 
happens in our houses, if we allow it to happen, almost every day 
during summer and autumn, and is the cause of a great deal of 
decay in fruits of different kinds, the disfigurement known as 
rust on Grapes, the damping-off of flowers and plants, and many 
other evils. In the dwelling house it is the source of rusty fire- 
irons, damp clothing, spoiled pianos, and endless colds. 
The remedy for all is the same—to guard against sudden fluc¬ 
tuations of temperature. A little fuel to keep up the temperature 
of a dwelling house during cold weather saves many an aching 
heart and a heavy bill. I often hear people complain, “ Oh ! my 
house is so damp, it gives me the rheumatism ; yet I always keep 
a good fire during damp weather.” The mistake is a very general 
one, and as damp weather frequently comes after frost the saddle 
is put on the wrong horse. When a sudden change of weather 
comes after frost I take care not to remain long in any building, 
public or private, which I know has not been kept well warmed, 
and the younger members of my family have the benefit of an 
absence from school till the dew at least has taken its departure 
from the inside walls of that building.— Wit, Taylor. 
ASPARAGUS IN AUTUMN AND WINTER. 
As a vegetable of the highest class there is nothing in our gar¬ 
dens more generally esteemed than Asparagus. It is easily cul¬ 
tivated, and may be grown to give a supply over a period of 
almost eight months—namely, from early in November till June. 
This autumn being so exceptionally wet and sunless, we were 
rather doubtful whether our Asparagus crowns would be matured 
and submit to early forcing, but they have stood the test well and 
promise to be very satisfactory. On October 21st we cut the 
withered 6tems from three or four dozen plants. They were then 
lifted and at once transferred to the bed of a Cucumber pit. Here 
the bottom heat averages 65°and the surface temperature 10° less. 
Over the slates in the bed a thin layer of soil was spread, and on 
this the roots were placed together closely, lightly covered with soil. 
In a few days many young crowns could be seen pushing through 
the soil, and on the 4th of November the first dish was cut. The 
heads were good, and looked both tender and sweet. This is one 
of the best ways of forcing Asparagus we have ever practised, and 
if we continue to put two or three dozen roots in fortnightly we 
shall be able to cut two or three dishes weekly so long as needed. 
Respecting the roots it may be well to say a few words. Had 
the plants been grown on the old-fashioned system, and so close 
together that the ground could not be seen between them in sum¬ 
mer, we should not have expected them to produce useable heads 
at this season ; but our Asparagus is growing now on what is 
known as the trench system. When one year old they were 
planted 3 feet apart each way, and now when they are three and 
four years old we are lifting every alternate one for forcing. At 
this rate the permanent rows stand 6 feet apart. It is in this 
way that large crowns are developed and become thoroughly 
ripened in autumn. One large crown every 6 feet will give more 
produce, and that of a very superior character, to roots 1 or 
2 feet apart. Crowding vegetables is a mistake in every case. I 
have mentioned the permanent plants as standing 6 feet apart, 
