As I stated in our last lecture, much interest is being awakened, in this
country and in Europe, by recent investigations showing the enormous
numbers of untimely deaths that are caused throughout all classes of
society by foul air.
It would have been a startling announcement, ten years ago, to have
stated that impure air caused as many deaths, and as much sickness,
as all other causes combined, and yet the most diligent and accurate
investigations are rapidly approaching that conclusion.
Few really comprehend the immense pecuniary loss, to say nothing of the
amount of suffering, that we endure by this extra and easily preventible
amount of sickness.
I propose, this evening, to enter upon the consideration of one of the
most important parts of our subject--_the effect produced by_ HEAT _upon
the movements of air_.
I think it probable that many of us do not comprehend the actual reality
of the air.
We are apt to say of a room that has no carpet and furniture in it,
that it has nothing in it, while, if it is full of air, it has a great
deal in it.
A room between twenty-seven and twenty-eight feet square contains one
ton of air--a real ton, just as heavy as a ton of coal. Now, there is
not only twenty-seven feet, but more than twenty-seven miles of air
piled on top of us. The pressure of the atmosphere at the level of the
ocean is about fifteen pounds to the square inch. An ordinary sized
man sustains a pressure of about fifteen tons, and were it not that
this pressure is equal in all directions, we would be crushed thereby.
We must accustom our minds, therefore, to consider air a real substance,
and that it is as totally unable to move itself, or to be moved, without
_power_, as water or coal. It requires just as much power to move a ton
of _air_ from the cellar to the second story, as it does a ton of coal.
Heat is the great moving power of air. Those whose attention has not
been especially directed to the subject of the amount of power exerted by
the sun's rays upon the earth, have little conception of its magnitude.
The power of all the horses in the world, added to the power of all the
locomotives, and of all the immense steam engines in all the world,
express but a small fraction of the power exerted by the sun's rays
upon the earth. It is estimated to be sufficient to boil five cubic
miles of ice-cold water every minute.
His rays are the chosen power of the Creator for moving all matter
upon the globe. It is his rays that lie buried in the vast coal fields
beneath the earth. His rays cause every spear of grass to grow, rear
the mighty oak, form the rose, burst its beautiful buds, and send its
perfume through the air.
No bird warbles its sweet music in the air, no insect breathes, save by
his power, and all animals love to bask in the genial glow of his light
and heat. He rolls the scorching air of the tropics to frozen lands,
and wafts the ships across the seas. He forces the heated waters of the
equator to the poles, tempering all the earth. He lifts the water from
the sea to sprinkle all the land and cap the distant mountains with
eternal snow.
Now, let us examine a little more minutely how this influence is exerted
upon the _air_, which is the subject we are especially interested in
at present.
Does it commence at the top, and heat it, layer by layer, until it reaches
the bottom? Not at all; but it passes through the whole forty-five
miles of air, heating it very little, if any, and falls upon the solid
substances at the earth's surface, heating them, which, in turn, heat the
air by its individual particles coming into immediate contact with those
solid hotter substances.
We will endeavor to illustrate this in a crude way.
[Illustration: Fig. 7.]
Here we have a tin tube, _a_, fifteen feet long and ten inches in
diameter, open at both ends; two feet from one end we introduce this
ascending pipe, _b_, the upper end of which is merely inserted in a
small flue, extending to the top of the building. The height of this
flue is sufficient to make a current of air pass through this tube,
as you will see by holding this smoking taper at the far end. We will
now place a large heated ball, _c_, at this end, and outside of that we
will place this reflector, _d_, pressing it quite close to the end of
the tube, so that no air can enter here.
The rays of heat from this ball, or from any other warm body, are thrown
like rays of light, in every direction equally; there would, therefore,
be some of the rays thrown through this tube to the other end without
any reflector, but the proportion that would reach the other end would,
of course, be small.
We therefore collect those going the other way, and change their course,
and then send them straight through the tube to the far end.
We will place another reflector, _e_, at the far end, to receive and
concentrate those rays, in the focus of which we will place a candle,
F, with a little phosphorus on it, to show you that the rays of heat are
passing through.
There you see the candle is lighted, thus proving that there is a
strong current of radiant heat coming from the hot ball, through the
tube to this end. And you see by this smoke that there is a current of
air passing the other way.
Now, we want to know how much that air is heated in passing the whole
length of this tube against that shower of radiant heat, or whether air
absorbs radiant heat at all; but, before going to the other end, where
the hot ball is, we will take two thermometers that have been lying here,
side by side, both indicating a temperature of 69 deg.. One of them, _g_,
we will hang at this end, about opposite to the centre of our tube,
which, I think, will give us a fair average of the entering air, first
removing, however, the candle that has been lighted, and the reflector.
We will hang the other thermometer in the ascending tube, at the end
near the heated ball. We have had two glasses, H, inserted here, so
that we might observe what was going on within by the smoke from this
taper. You see there is a strong current of air passing up the tube,
all of which must come from the far end, flowing against the strong
current of radiant heat going in the opposite direction. Now, leaving
this thermometer to rise or fall according to the temperature of the
air flowing through, we will go to the other end and examine another
very interesting part of this experiment: it is the manner in which the
radiant heat is received and appropriated by different substances.
Radiant heat is thrown from a hot body in every direction equally, but
no two kinds of substances receive those rays of heat in the same manner,
nor do they make the same use of them after they have received them.
Every substance receiving heat, however, must give a strict account of
it. It must give out an equal amount of heat, or, what is taken as an
equivalent, some action or power.
I have a sheet of ordinary tin, and as I hold this polished side behind
this light, you see it throws a belt of light across the room; and as
I put it in front of the end of our tube, and turn it so that the rays
of heat will be reflected in your faces, I think some of you will be
able to feel the reflected heat. The rays of heat are turned from their
course, and thrown in a belt of light across the room, similar to the
rays of light.
But you cannot give away and keep the same thing. This bright polished
surface appropriates but a very small portion of the radiant heat. A
thermometer hanging for some minutes against the back has scarcely risen
one degree; but we have given the other side a coating of lamp black,
with a little varnish, and by turning that side towards the pipe, the
result will be quite different. By this coat of black varnish the whole
character of the sheet of tin is changed. The black, however, has but
little to do with it; if it were white, or red, or blue, the formation
of the surface being similar in every respect, the result would be the
same almost precisely.
Instead of acting merely as a guide-post, to _change_ the _direction
only_ of the rays of heat, as before, it now becomes a receiving depot,
absorbing nearly all the heat that comes to it. It must soon become
filled, however. The thermometer hanging at the back has risen six
degrees already, and is going up rapidly; it must soon begin to distribute
its extra stores. But mark the different manner of distributing the
heat. Instead of _reflecting_ the whole all in one direction, as when
received on the other side, it now _radiates_ them equally in every
direction.
Some solid substances allow the rays, both of heat and light, to pass
directly through them without either reflecting or absorbing them. Other
substances allow the rays of light to pass through them, but absorb much
of the radiant heat, like clear glass.
Rock salt is one of the best non-absorbents of radiant heat, allowing
nearly the whole of the rays of heat to pass through unobstructed.
We will now return to our experiment at the other end of the tube. I
find there is something wrong here--the mercury in the thermometer has
risen several degrees. I knew this was rather a crude arrangement for
illustrating this very beautiful and interesting part of our subject,
but I hoped it would assist me a little in conveying to you the idea I
desired to impress upon your minds. I find, however, that it is scarcely
delicate enough to illustrate perfectly what I wanted to show.
But this increased temperature is not owing to the effect of radiant
heat on the air coming from the far end, for I find by the heat at the
top of the pipe, between the heated ball and this ascending pipe, I, and
by the current of heated air on the side next the ball, that there is
a current of _circulating air_ that _has been heated_ by coming into
immediate _contact_ with the hot ball.
I designed this smaller tube, _k_, to carry off the air thus heated, but
it appears to be too small.
We ought to have had a piece of rock-salt to have closed the end of
this tube, so that the radiant heat would have passed through without
allowing any _circulation_ of _heated air_, but I was unable to find
such a piece. But Professor Tyndall, in his lectures before the Royal
Institute of Great Britain, gives the results of a large number of very
accurate and beautiful experiments tried for the purpose of determining
whether the forty-five miles of atmosphere surrounding the earth absorbed
_any_ of the sun's rays, and if so, how much?
These experiments prove, in the most conclusive manner, that dry pure
air is almost a perfect non-absorbent of radiant heat. Thus, were the
air entirely dry and pure, the whole forty-five miles through which the
sun's rays have to pass, would absorb a very small fraction thereof,
so that in the length of our tube it would be but an exceedingly small
fraction of one degree, that is, for pure dry air.
But is the air of this room pure and dry? Very far from it.
Professor Tyndall found that the moisture alone in the air of an ordinary
room, absorbed from fifty to seventy times as much of the radiant heat
as the air does. Air and the elementary gases--oxygen, hydrogen and
nitrogen--have no power of absorbing radiant heat, but the compound
gases have a very different effect; for instance, olifiant gas absorbs
7950 times as much as air; ammonia, 7260; sulphurous acid, 8800 times.
Perfumes, also, have a wonderful power of absorbing radiant heat.
The moisture in the air, however, is of the greatest practical importance
in various ways. It is the great governor or regulator or conservator
of heat; it absorbs it and carries it from point to point and into
places where the direct rays of the sun could not get; it is like a
soft invisible blanket constantly wrapped around us, which protects us
from too sudden heating or too sudden cooling.
Professor Tyndall, speaking of the moisture in the air, says: "Regarding
the earth as a source of heat, no doubt at least ten per cent. of its
heat is intercepted within ten feet of its surface." He also says:
"The removal for a single summer's night of the aqueous vapor from the
atmosphere which covers England, would be attended by the destruction
of every plant which a freezing temperature could kill.
"In Sahara, where the soil is fire and the wind is flame, the
refrigeration is painful to bear."
And in many of our furnace-heated houses, we have an atmosphere very
similar in point of dryness to that of Sahara, but more impure.
The foregoing remarks in regard to the impossibility of heating air,
apply especially to radiant heat. Air does become heated, but in
a different manner; it is heated by each individual particle or atom
coming in immediate contact with some hotter substance. See what a
wonderful provision for creating a constant circulation of the air.
The sun's rays pass through it without heating it, but they heat the
surface of the earth at the very bottom of the ocean of air; this, in its
turn, heats the air by each individual atom coming in immediate contact
with these hotter substances, expanding them so that they must rise,
thus enabling the colder and heavier particles to rush in and take their
places. With this great universal moving cause, in connection with the
innumerable minor causes resulting from the very different absorbing,
radiating and reflecting powers of various substances, it becomes
almost impossible for the air to be entirely and absolutely at rest,
even in the most minute crack or cranny, or bottle corked air-tight.
Now, to apply these principles to every-day life, to the heating and
ventilation of our houses, taking the _open fire_ first, we find that
it acts like the sun, heating exclusively by direct radiation. The rays
of heat fall upon the sides of the room, the floor and ceiling, and
the solid substances in the room, which thus become partially heated,
and in their turn become _secondary radiators_. This radiant heat from
the fire does not heat the air in the room at all, but the air becomes
partially warmed by coming in immediate contact with the sides of the
room, the furniture, &c.
One great reason, therefore, why an open fire is so much more wholesome
than any other means of artificial heating, is because it more nearly
imitates the action of the sun.
The rays of heat fall upon our bodies, heating them, while it leaves the
air cool, concentrated and invigorating for breathing. The bright glow
of an open fire has a very cheering and animating effect. It produces
a very agreeable and healthy excitement.
It is not improbable that future careful investigations may prove that
there is an important change takes place in the electric or ozonic
condition of air as it passes over, or in contact with, hot iron, which
does not occur to the air of a room heated by the open fire.
The air in a room heated by an open fire can scarcely become stagnant,
because that fire must necessarily be constantly drawing a considerable
amount of air from the room to support combustion, the place of which
will be supplied by other air, and here is where one of the greatest
inconveniences arises in the use of the open fire; if the air entering
to supply this exhaustion comes in at a crack of the door or window,
on the opposite side of the room, and that air is cold, say 10 deg. or 15 deg.
above zero, it flows across the floor to the fire, chilling the feet
and backs of those sitting in its track. It is quite possible to roast
a goose or round of beef in front of a fire, while the air flowing by
it into the fire is freezing cold. This should be remedied by having
the air flowing in partially warmed before it enters, say to a
temperature of 40 deg. to 50 deg., either by having the halls overflowed by
partially warmed air, and opening a door into it, or by admitting the air
to enter around the back of the fire-place, as Dr. Franklin arranged it.
Thus, while an open fire is the healthiest known means of heating a
small room, and should be in the family sitting-room of every house,
and in offices and other places where the occupants are at liberty to
move closer or further from the fire at pleasure, yet it is entirely
unsuitable for a large building, or for rooms where many persons are
assembled, and have fixed seats, similar to a school, lecture-room,
factory, &c.
A stove in a room heats both by direct radiation and by heating the air
that comes in immediate contact with it.
But our latest styles of elegant new patent gas-consuming air-tight
stoves, require so small an amount of air to support combustion, that
there is a strong probability of the occupants of a room thus heated
smothering to death for want of fresh air, sooner or later, and generally
the former.
But a stove, if properly used, creates a comfortable and wholesome
atmosphere, and is one of the most economical means of heating now
known. There should always be a separate pipe for introducing the fresh
air from the external atmosphere, which fresh and cold air should be
discharged on or near the top of the stove. And if this supply of fresh
air is abundant, with a constant evaporation of moisture sufficient to
compensate for the increased capacity therefor due to the additional
heat given it, and an opening into a heated flue near the ceiling, to be
opened in the evening when the gas-lights are burning, or when the room
is too hot, and kept shut at all other times, with another opening into
a heated flue on a level with the floor, which should be kept _always
open_ to carry off the cold, heavy foul air from the floor--a stove
thus arranged for many small isolated rooms, makes one of the most
economical as well as most comfortable and wholesome means of heating
at our command. It combines the three great essentials necessary for
comfort and health--_warmth_, partially by direct radiation, _fresh air_
and _moisture_. But neither the open fire nor the stove, as desirable as
they may be in many small rooms, are suitable for large rooms, especially
where many persons are assembled. Heating principally by circulating
warmed air, or in combination with direct radiation from exposed pipes
filled with steam or hot water, is in such cases more convenient.
It is in connection with this system of heating by circulating warm air,
that the erroneous views in relation to ventilation generally entertained
by the public, produce the most injurious effects.
The special points to be borne in mind in considering this subject are
that, when in motion, warmer air rises and colder air falls; but when at
rest, the stratums of air of different temperatures arrange themselves
horizontally.
One other thing: we must remember _temperature_ has nothing to do with the
purity or impurity of the air. The pure air entering a room is _sometimes_
colder than the average temperature of the room, and falls to the floor,
forcing the warmer, and, in that case, fouler air to the upper part of
the room.
But frequently, in winter, the fresh air enters _warmer_ than the average
temperature of the room, and _rises to the ceiling_, and flows across
the room above the colder and fouler air that has been longer in the
room. You must not forget the experiments in our first lecture, showing
that the breath in an ordinary room, of a temperature of 70 deg., fell to
the floor instead of rising to the ceiling. I propose illustrating this
part of our subject, by using a little glass room to show the movements
of air of different temperatures. We can either use air of different
temperatures, showing the motion of the various currents by a little
smoke; or, as the laws governing the circulation of liquids of different
densities are so similar, and by the use of a little coloring matter
will express to an audience of this kind more promptly and clearly the
ideas which we wish to convey, we therefore propose using the different
colored liquids this evening.
The colors, of course, have nothing to do with the densities, but are
merely used as a convenient method of designation; the red representing
heat or rarity, and blue, coldness or density.
The room is now filled with clear water, slightly blue, to represent
cold, and a little salt, which makes it a little more dense than fresh
water. Now, I will let in at the top a little fresh water, colored
red by cochineal, to represent heat, and by making a similar opening
on the opposite side for its escape, you will be able readily to see
in what direction it moves. There, see it entering--see how it flows
directly across the top of the room, and escapes at the opening on the
opposite side. You see it disturbs the lower and colder parts of the
room but very little. Thus a large flow of pure fresh warm air might be
going through a room all day, and be entirely wasted, neither warming
nor ventilating it. Fortunately, there are but few buildings arranged in
quite so absurd a manner as this. I believe it was tried in the House of
Lords, on the erection of the new Houses of Parliament, but, of course,
failed. I think they still adhere to it in some of the wards of some
Insane Asylums, where they depend, I suppose, upon the excitement of the
patients to keep themselves warm and the air stirred up. I also noticed
this arrangement in a new building just being finished, a few years
since, at Yale College. The architects of that building had probably been
impressed with the dreadful effects upon the health of students of the
air from our ordinary hot air furnaces, and thought they would avoid all
such danger. I think, however, it would have answered their purpose just
as well, and been much more economical, to have placed the furnaces at
the coal mines, and saved the trouble and expense of carrying the coal so
far. I expect they have made other arrangements, probably, by this time.
[Illustration: Fig. 1]
[Illustration: Fig. 2]
[Illustration: Fig. 3]
We will now close the opening at the top for the _inlet_ of the fresh
warmed air, and open a valve, so as to allow it to flow in at the bottom.
We will allow the opening at the top for the _outlet_ of the foul(?)
air to remain as before, (see Fig. 1, Lithograph plates.) This is quite
an improvement; it agitates the air much more than the other, and by
going and standing directly over the register, you can always get in the
current of fresh warm air. But you see to what a very small portion of
the room the heated air is confined, rising in one perpendicular column
directly to the ceiling, and then flowing horizontally along the ceiling
to the outlet. How little it disturbs the main portions of the room,
especially the lower and occupied part.
I hope you will notice that this illustrates the popular notions of
ventilation. I suppose three-fourths of all the buildings in this country,
or in Europe, where any attempts at artificial ventilation have been made,
are thus arranged. Dr. Franklin knew better, and made a much more perfect
arrangement than this. But we are probably mostly indebted to that very
able and enthusiastic advocate of ventilation, Dr. Reid, for this popular
opinion. The whole of the plan that he advocated is but little understood
by the public. He assumed that the natural warmth of the body created an
ascending current around us, and caused the breath to rise towards the
ceiling, and consequently, in all artificial arrangements, it was best
to endeavor to imitate this natural movement of the air. And to overcome
the great practical difficulty we see here exhibited, of the fresh warm
air flowing through the room, and disturbing so small a portion of it, he
proposed making the whole floor one register, and thus have an ascending
column over the entire room. For this purpose, the floors in the Houses
of Parliament were perforated by hundreds of thousands of gimlet holes,
and the whole cellar made a hot air chamber. This was a magnificent
idea, and, I believe, in some few instances, where fully carried out,
has given a good degree of satisfaction; but it is always difficult to
adjust the opening and the pressure so as to cause an even flow over
so large a surface, and at the same time to be so gentle as not to be
offensive to those with whom it comes in contact. But this thorough
diffusion cannot be conveniently applied in one case in a thousand. It
must necessarily be always very extravagant, as it will constantly require
a great amount of air to insure a thorough circulation through all parts
of the room. I wish, therefore, most emphatically, to condemn all systems
relying upon openings in the ceiling for the escape of the foul air,
while depending upon the circulation of warmed air for obtaining the
necessary additional warmth. In practice they are universally closed
in winter, for the purpose of keeping warm, and as such openings have
been so generally considered the _only_ ones necessary for the proper
ventilation of a room, and as they had to be shut in winter, just when
artificial ventilation was most necessary, it has created a very strong
prejudice in the popular mind against all ventilation.
The result of the advocacy of these impracticable theories by so many
able and learned men, (most physicians writing upon this subject have
adopted them,) has been the shutting up of many thousands and tens of
thousands, till they have smothered to death.
The ravages of consumption and the excessive infantile mortality, and the
many diseases resulting from foul air poisons, are in a great measure
due to the general advocacy of these false theories. As I have before
said, Dr. Franklin knew better than this, and had we been contented to
have followed his simple practical advice, instead of being dazzled by
the splendid theories of others, thousands of our friends would now be
with us who died long since for the want of fresh air.
Now, let us see how Dr. Franklin says a room ought to be ventilated.
He says, "the fresh air entering, becoming warmed and specifically
lighter, is forced out into the rooms, rises by the mantel-piece to the
ceiling, and spreads all over the top of the room, whence, being crowded
down gradually by the stream of newly warmed air that follows and rises
above it, the whole room becomes in a short time equally warmed." This is
the principle upon which his celebrated Franklin stove was arranged. Now,
let us see if we can arrange our little glass house so as to illustrate
this. We will first fill it with what we call our cold air, and will
close the outlet at the top, and take out the fire-board. Now, as I
let in the warm fresh air, it rises immediately to the top, as before,
and flows across the ceiling, but as it cannot escape there, it forces
the cold air down, and causes it to flow out at the fire-place. See how
quickly the whole room is filled with the fresh warmed air. Ah! I see
I am a little too fast--there appears to be a stratum of a foot or two,
lying on the floor, that is not disturbed yet. It flows out at the top
of the fire-place, and therefore does not reach to the floor. This is
frequently the cause of cold feet and much discomfort. We will make the
opening directly at the floor, (see Fig. 2, Lithograph plate,) and that
forces all the cold air out, warming and ventilating the whole room. Here
is the whole problem solved in the most beautiful and simple manner.
And you may exclaim, as you see the simplicity and perfect working of
this, how came any one ever to think of anything else.
Here, again, you see the value of that most excellent and valuable of
household arrangements, the open _fire-place_; even without the fire it
serves a most important purpose.
[Illustration: Fig. 4]
[Illustration: Fig. 5]
[Illustration: Fig. 6]
We must not forget, however, that there are other circumstances in
which it will not do to depend on the fire-place alone for ventilation.
Now, by leaving the fire-place open, just as it is, and the room full
of warm air, we will simply change the _condition_ of the air supplied,
and allow cold air to flow in at the bottom instead of the top. (See Fig.
3.) There, you see the fresh _cold_ air simply falls to the bottom and
flows across the floor, without disturbing the upper part of the room at
all. It acts just the reverse of the hot air let in and taken out at the
top of the room. When you are ventilating a room by _opening a window_,
therefore, it is often necessary to open it at the top; but remember
when you are ventilating by doors and windows, (which are the great
natural ventilators,) _they_ are an entire substitute for flues--flues
are then of no account. All _windows_, therefore, ought to be made to
_lower from the top_, and all ventilating _flues_ ought to be made to
_open at the bottom_ of the room.
I have noticed another very interesting feature in regard to the
circulation of liquids of different densities; for instance, suppose we
fill our little room half full with salt water, and the remainder with
fresh water, we will now apply a spirit lamp to the bottom of the room.
As the salt water becomes heated it rises rapidly, yet not to the top of
the room, but only half-way, or to the top of the denser liquid, and then
spreads across the room horizontally. Thus the salt water will keep up
a rapid circulation, and may be heated almost to a boiling temperature
_underneath_, and without heating or disturbing, the cold fresh water
_above_. I have tried some very beautiful experiments of this kind with
a number of liquids of different densities in the same vessel. Gases
of different densities are probably influenced in a similar manner by
the application of heat. And here we see the value of that beautiful
law of the diffusion of gases, by which each gas, no matter what its
density, is equally diffused in all directions through the other gases,
independent of temperature.
I desire to call your attention this evening to one other distinct
system of heating--I mean that very convenient, economical, cleanly and
FASHIONABLE system of heating by direct radiation from steam-pipes.
As steam has become such a common article in all large buildings, both
for power and as a convenient means of distributing heat, most large
buildings are thus heated; and as a perfectly air-tight building can be
very easily heated thus, and as most persons are too ignorant or too
careless to provide a separate and distinct supply of fresh air simply
for ventilation alone, the consequence is, that this system, thus
so shamefully abused, is probably drying up more talent and killing
more business men in our cities than any other system in existence.
This applies especially to the editorial rooms of nearly every one of our
leading newspapers and publishing houses. They use steam for driving their
beautiful printing presses, and the heating and ventilation, or rather,
the entire want of ventilation, in their offices, would indicate that
they think that the same power that drives their presses, to do the
printing so nicely, is entirely sufficient to drive them to write the
original articles for the printer, and that they have no more need of
_fresh air_ than their presses.
You may think that I am certainly mistaken that so intelligent a class
of the community, who are building such splendid fire-proof buildings,
such perfect palaces of iron and stone and marble, as our newspaper
establishments are building in New York, Philadelphia and other large
cities, would never make such a blunder as to omit providing the
most abundant supply of pure, fresh air to every employe in their
establishments, and at all times, both in summer and winter.
Should there be any one present thus doubtful, I wish he would undertake
to get any one of our enterprising newspaper establishments to publish
in their paper an accurate intelligible account of their system of
ventilation, illustrating clearly the known quantity of pure, fresh air
delivered within using distance of each one of the editors and employes.
I think he would soon come to the same conclusion I have, that the
advice of the minister to his congregation would be very applicable to
them--"Always do as I _say_, but never do as I _do_."