covers its face. This glass is easily moved around in its metal rim,
bringing the hole over any desired minute upon the face. One wire
of the battery is attached to a leg of the clock, the other goes to
a bell, and then the wire from the bell is poked through this hole.
When the minute hand reaches that point the electric current is closed
through the metal of the clock, and the bell rings warning that the
eggs, coffee or what not are done.
We each urged that our memories should share in the vacation, and
applied for one of these outfits. I took one of the clocks and cut back
the minute hand so as to make it shorter than the hour hand, and then
had the hole in the glass made so that the hour hand should close the
electric circuit. This was kept at my study table and reminded me of my
appointments. Some used these clocks to alarm themselves in the morning
when they slept overtime.
Another reminder is shown in Fig. 176. _C_ is a float which rises and
falls with the water in our house tank. A cord running over two pulleys
connects this with a weight, _d_, hanging in front of a scale upon the
wall of the kitchen. This indicates how much water there is at any time
in the tank, which is situated in the garret. The boys arranged a bell
and battery so that when the tank is nearly empty the weight _d_ will
pull upward a spring, _a_, and make it close the circuit through the
bell to warn that water must be pumped. When the tank is nearly full
the weight _d_ pushes down the spring _b_ and rings the bell again.
[Illustration: Fig. 176]
Harold said that yeast cakes were the heaviest tax upon our memories.
If some one started for the village store, before he got out of
hearing, a call would come after him, "I forgot the yeast cake. Please
put that on the list." When one returned from the village store
with numerous packages, he would generally hear, "My yeast cake was
forgotten." We tried all sorts of schemes to get rid of this yeast-cake
nuisance, and finally adopted Harold's "curled bread" project.
We had built a brick oven out back of the house for experimental
purposes. Harold proposed that the boys bake a month's supply of bread
at a time, and, when it was a day or two old, cut it all into thin
slices and let it dry. These slices curled up as they dried and were
known as "curled bread." A flour barrel was filled with it each month.
It kept perfectly any length of time. The family voted it to be better
than crackers and better than fresh breadstuff of any kind.
Harold's suggestion regarding yeast cakes worked so well and was such
a relief to our memories that I proposed he next attack the problem of
the often forgotten salt in cooking.
XX
THE ELECTRIC BRICK OVEN
We had no end of experiments with brick ovens. One of the most
interesting was that wherein we used the brick fireplace as an oven
and did the family baking in it. On a cold morning we would build up a
smart wood fire in the fireplace and enjoy it during breakfast time.
Then we shovelled out the coals and the ashes, and shut it up tight
with a sheet iron arrangement and utilized the heat stored in the
bricks for doing all sorts of cooking.
Our outdoor brick oven and our monthly baking day were such a success
that they led to the construction of another oven of smaller dimensions
for the kitchen. This one was heated by electric lamps--one in each
of the eight corners. It had double glass doors in front so that the
cooking process might be watched. The glass of the inner door would be
clouded with moisture for a while, when the cooking first began, but
this would soon clear up, and then the lamps enabled us to watch the
colour changes in baking, etc. The lamps in the upper part of the oven
were connected with a different switch from those in the lower part of
the oven, so that we were able to control the browning on top or bottom
at pleasure.
Harold introduced a device for automatically controlling the
temperature of this oven.
[Illustration: Fig. 177]
Strips of brass and iron, _B_ and _I_ (Fig. 177), were riveted
together. These were fastened in the socket _A_. They are shown
edgewise in the diagram. The upper end of this compound strip is free
to bend back and forth in the plane of the paper, as here represented.
They normally touch the screw _C_. One of the electric light wires runs
from the lamps in the oven to this screw _C_. One wire of the dynamo
circuit _G_ goes to the lamps, and the other connects with _A_. Thus
the compound strip acts as a switch to open and close the circuit upon
the lamps.
This thermostat, as it is called, was placed inside of the oven.
Heat causes brass to expand more than iron and therefore when the
temperature reaches a certain height the thermostat curves, so as to
break the contact with _C_, and the lamps go out. When the temperature
falls a little the thermostat straightens until contact is again made
with _C_. _C_ is a screw and can be made to advance or recede in its
socket _E_, so that the temperature of the oven may be maintained at
any point desired. The wire of the screw _C_ extends to the outside of
the oven, where it carries an index, _D_, over the face of a dial, as
shown in Fig. 178.
[Illustration: Fig. 178]
The cook may set this index at any desired degree, and the lamps will
indicate when that degree has been reached. The thing to be baked is
then put inside and the clock, illustrated in Fig. 175, is set so as to
warn when the time is up.
The electric spark which occurs when the thermostat breaks contact with
_C_ causes the metals to corrode at that point, and corroded metals
are poor conductors. This corrosion is due to the oxygen of the air.
There is one metal--the expensive platinum--which is not corroded by
the electric spark. We drilled small holes in the end of the screw _C_
and in the brass strip and pounded into these holes little pieces of
platinum wire. Harold said he felt like a dentist filling a tooth. This
furnished good, clean contact at all times.
It takes a long time to heat up the brick oven, but it holds its heat
a long time and makes an excellent fireless cooker after the lamps are
turned out. It does not allow heat to escape into the kitchen, which
makes it a comfort in our summer cottage. We are all becoming daft on
_slowly cooked_ food--a sort of ripening process which gives time for
the chemical changes to take place and develops the finest flavours of
the food.
XXI
ELECTRIC WAVES
Much has been said about bringing young people up to do what they don't
like to do so as to make them strong and virtuous. My own life has
always been guided by a different principle. It is: _Find something
worth while which you will enjoy doing, and do it with your might._ I
am bringing up my boy on the same principle. In September we have a
real desire to get back to our work in the city, and in June we have
an eager longing for the occupations of Millville. I am not aware that
there is any part of my work which I would like to be relieved from,
and Harold and his mother said that they were now ready to return to
the city apartment with real pleasure for a winter.
One evening we were seated about the dinner table when Harold asked me
how electricity could travel without wires. I replied, "It travels as
light does. But I am very much puzzled to know why it ever follows a
wire when light does not." This did not settle the question and left
us both unsatisfied, so I told him to invite two or three of his best
friends in to-morrow evening, and I would perform some experiments for
them that would at least help them to think further upon this subject.
When the evening came I showed the boys an automobile spark coil to
which I had attached two knobs, _a_ and _b_ (Fig. 179), and with which
I had connected two dry battery cells. When I touch the wire _c_ to
the binding post _d_ a spark passes between the knobs _a_ and _b_.
When this spark occurs at least four kinds of waves pass out in all
directions from the spark gap between the knobs.
[Illustration: Fig. 179]
First, sound waves go through the air. Our ears detect these. If the
air is removed from around the apparatus no sound wave can go forth. A
careful examination of the internal ear shows us that it is constructed
so as to respond to such air waves.
Second, light waves go forth. These affect our eyes. We are blind to
the first kind of waves and deaf to the second. The light waves travel
without air--somewhat better without air than with air. A microscopic
examination of the eye indicates that it is constructed so as to
respond to waves. We believe there are waves in the ether which fills
all space. Sound waves travel in air at the rate of one mile in five
seconds. We had this nicely illustrated at the sea shore one summer.
The steamer touched each morning at a wharf which we could plainly
see two miles distant. We could see the steam arise when she blew the
warning whistle, and with our watches we found that it always required
ten seconds for the sound to reach us after we saw the steam of the
whistle. This at least showed us that it takes five seconds longer for
sound waves to travel a mile than it does for light waves to travel
the same distance. For light had to travel the same distance before we
could see the steam arise from the whistle. Although the time it takes
for light to travel a mile is inconceivably small, we have a simple
method of finding out that it requires eight minutes for light waves to
come to us from the sun.
The satellites of the planet Jupiter, in revolving about that body,
disappear and reappear at regular intervals, acting as flash lights to
mark time.
[Illustration: Fig. 180]
The earth, being 92,000,000 miles distant from the sun, is 184,000,000
miles farther from Jupiter when at _B_ than it is when at _A_. (See
Fig. 180.) It is found by observation that sixteen minutes more are
required for the light waves from a reappearing satellite to reach us
at _B_ than when we are at _A_. Hence eight minutes would be required
for light waves to travel the distance from the sun to the earth.
Although light travels at the inconceivable velocity of 186,000 miles
per second, the nearest star is so far distant that it takes light
three and a half years to come from it to us. The North star requires
forty-two years to send its light to us, and Arcturus is so far away
that waves of light sent out from it one hundred and sixty years ago
are only just reaching us now, and if it should cease to send forth
light now men would continue to see it for five generations yet to
come.
A third kind of wave which goes forth in the ether from the spark gap
of our coil is a heat wave. This affects neither our eyes nor our ears,
but I will undertake to make you conscious of it by another method.
[Illustration: Fig. 181]
Before a mixture of gasolene vapour and air can be ignited its
temperature must be raised to about 2000 degrees Fahrenheit. I will
show that heat waves pass out from this spark gap by placing my watch
crystal filled with gasolene underneath the knobs of the spark coil,
(Fig. 181). When now I close the electric circuit at the battery the
mixture of gasolene vapour and air just above the watch crystal is
ignited. If I increase the distance between the knobs you still hear
the crackle of the sound waves and see the light waves, but the mixture
of gasolene vapour and air does not ignite, because there are not heat
waves enough. The automobilist expresses this fact by saying a "fat"
spark or a "warm" spark is needed. A battery which has ceased to give
a sufficiently hot spark to explode the mixture of gasolene and air in
the cylinder of a gasolene engine may serve all other purposes quite
as well as ever. It may ring bells almost as long as it ever would.
I proved that the temperature for igniting a mixture of gasolene vapour
and air was nearly as high as melting iron, by heating an iron rod to a
dull red heat and bringing it to the watch crystal containing gasolene.
It did not take fire. I showed that it could not be ignited by a
lighted cigar, nor even by a glowing coal taken from the fire.
It was necessary to heat the iron rod to a very bright red heat--nearly
white heat, or nearly to its melting point, before it would ignite the
mixture.
These heat waves are ether waves, differing from light only in having
greater wave length. They travel at the speed of light, they travel
better without air than with air. They come from the sun and all other
light-giving bodies. Indeed, an ordinary incandescent electric lamp
gives out about twenty-four times as much energy in heat as in light.
Heat waves are being thrown off from all bodies which are around us.
The steam radiators are placed in this room for the express purpose
of sending out heat waves through the ether in this room. This is
the chief method of distributing heat, and it is hindered rather
than helped by the presence of the air. The walls, ceiling, floor,
furniture, people--everything here is sending out heat waves.
The fourth kinds of waves, which go out from the spark gap of our coil,
are also waves in the ether. They are still longer than heat or light.
We have ears for sound, eyes for light, and temperature sensation
for heat, but as yet we have not evolved a delicate sense organ for
detecting electric waves. At least few of us claim to have such a
sense. I will, however, undertake to make you feel electricity. I then
adjusted the coil so that each boy might take a mild electric shock
from it by touching the two knobs. That is by placing himself in the
spark gap. They agreed that although they could not hear, see, taste,
or smell electricity they were a little more familiar with it now,
having felt it.
Sound waves in air, as given out by the piano, vary in length from,
say, four inches to forty feet, those having the shorter wave length
being the higher pitched tones.
Light waves in the ether, as given out by the sun, vary in length
from, say, 1/60000 to 1/80000 of an inch, those having the shorter
wave length being the violet-coloured light, which may be seen in the
rainbow, and those having the longer wave length being the red-coloured
light of the rainbow or the sunset.
Heat waves, which are also waves in the ether, vary in length from
above 1/80000 to, say, 1/5000 of an inch. Roentgen or X waves are ether
waves, shorter than light; while Hertzian, or wireless telegraph waves
are very long ether waves, varying from a few feet to many rods in
length. Those used by Marconi in sending despatches across the Atlantic
Ocean are as long as 1000 feet, four or five of them cover a mile, and
12,000 of them cover the whole distance from Cape Cod to Poldhu.
Electric waves are easily broken up into the shorter heat waves, or the
still shorter light waves. On the other hand Roentgen waves are readily
transformed into the longer light waves, and are thus brought within
our powers of vision.
Sound waves of various lengths (of high and low pitch) all travel at
the same speed (one mile in five seconds), else how would the piccolo
and the bass horn of the distant band sound together. So ether waves of
various lengths (light, heat, electricity, etc.) all travel at the same
speed, _i. e._, 186,000 miles per second.
For detecting the electric waves which may be sent out from the spark
gap of our automobile spark coil I shall ask you to help me prepare
a special piece of apparatus. One boy may file this silver ten-cent
piece and another may file this nickel five-cent piece, each gathering
the filings upon a piece of paper. A third boy may select a piece of
glass tubing about one eighth of an inch in the inside diameter, and
with a three-cornered file cut off a short piece, about one and a half
inches long, and smooth the ends with a wet file. A fourth boy may
select a piece of stout copper wire nearly as large as the bore of the
glass tubing, and cut from it two pieces, each about two inches long.
Wind one end of each of these with thread to make them fit snugly in
the glass tubing.
[Illustration: Fig. 182 Coherer]
We thrust one of the wires into the tube, then mixed equal parts of the
silver and nickel filings and put as much of the mixture into the tube
as we could hold upon the tip of a penknife blade, and then thrust in
the other copper wire. (See Fig. 182.) The ends of the wire were about
one eighth of an inch apart and the gap was loosely filled with the
metal filings. This was connected by short pieces of copper wire, as
shown in Fig. 183, to a dry battery cell, _B_, and a sensitive ammeter.
When all connections were made the needle of the ammeter remained at
zero, showing that no electric current was passing, that is, the
battery cell was unable to send any electricity through the metal
filings.
This is the apparatus which is to help us detect electric waves when
they pass about us. Electricity has been called invisible light, that
is, invisible to our eyes, and this apparatus has been called an
"electric eye" because it will detect electric waves in the ether, just
as our eyes may detect light waves passing through the ether.
[Illustration: Fig. 183]
We placed the automobile spark coil upon the table near to the tube
containing the filings of silver and nickel, and as soon as we made a
spark pass between the knobs the ammeter needle moved half way across
the scale, indicating that the spark had somehow influenced the metal
filings in the tube so that now they permitted the battery cell to send
some electric current through them and through the ammeter. I asked one
of the boys to tap the tube slightly with a lead pencil so as to jar
the metal filings, and as soon as he did so the needle of the ammeter
went back to zero.
[Illustration: Fig. 184]
The spark coil sent electric waves out in every direction, and those
which hit the metal filings made them cohere together. In that
condition they allowed the dry cell to send through them enough current
to move the needle of the ammeter. Tapping the tube made the metal
filings break apart again, in which condition they do not allow the
current of the cell to pass in sufficient quantity to move the needle.
This tube is called a _coherer_, because the filings in it cohere
together. The apparatus then serves to indicate when electric waves
are passing. As yet, however, it would not respond when the spark coil
was more than one foot away. Our next step was to attach extra pieces
of wire, each ten or twelve feet long, at either end of the coherer,
as indicated in Fig. 184. One of these wires was stretched out upon
the floor while the other one was connected with the wire of a picture
hanging upon the wall.
We now found that the coherer would respond when the spark coil was
operated several feet away. The extra wires which we had attached to
the coherer are called antennæ, because they suggest the long "feelers"
or antennæ of some insects.
[Illustration: Fig. 185]
Our next step was to put antennæ upon the spark coil also, as shown
in Fig. 185. One of these wires was stretched out upon the floor,
while the other one was connected with the wire of a picture hanging
upon the wall on the opposite side of the room from where the coherer
was. We now found that the coherer would respond when the spark coil
was operated in the farthest part of the room. With the wires which
were lying upon the floor extending toward each other, but lacking
several feet of touching, the coherer responded when the spark coil
was operated in various other rooms of the house, although the doors
between were shut. When the floor wires were connected to the water
pipes the coherer would respond when the spark coil was operated in
a neighbouring house. We tried a similar experiment, substituting an
ordinary electric bell for the spark coil. The coherer or electric eye
detected that ether waves were sent forth from an electric bell every
time a spark was produced in the bell. For this purpose connections
were made, as shown in Fig. 186. One dry battery cell was used to ring
the bell. The floor wire _a_, or, as it is usually called, the ground
wire, was connected to the binding post 1, and the other antenna was
connected to the screw 3, and then supported aloft on a picture hung
upon the wall. With this transmitter we sent waves across the room
which were detected by the coherer.
[Illustration: Fig. 186]
We constructed a simple spark coil as follows: We bought a pound of
No. 24 single cotton covered copper wire, such as is used in the
electro-magnets of bells. It was, when we bought it, wound upon a
wooden spool. We filled the hole in the centre of this spool with wire
nails. One dry cell was connected with this (Fig. 187). When the wires
at _d_ were touched together, and then separated, a spark was produced
at that point. A ground wire was connected at _b_, and an antenna at
_c_, as before. Using this apparatus now as a transmitter of ether
waves, we found that the coherer detected them.
[Illustration: Fig. 187]
We next gave our attention to making changes in the receiving
apparatus, not to change the coherer, but to provide substitutes for
the ammeter. A sensitive _relay_ was procured, which is essentially
like a bell or buzzer except that it does not clatter. It will be
readily understood, by referring to the accompanying Fig. 188, that
_R_ is a coil of insulated wire around an iron core exactly like what
we see in the electric bell. (In practice there will be a pair instead
of one of them.) Such coils are called electro-magnets, because when
electricity flows in the wires they become magnets, and will attract
iron. _A_ is an iron spring, _B_ is a dry battery cell and _C_ is the
coherer. Whenever an ether wave passes the coherer permits the battery
cell to send a current around the magnet of the relay, and it attracts
the iron spring _a_, so that it hits against the metal post _d_ with
a click. Whenever we used this to respond to ether waves the click of
the relay suggested the telegraph sounder. How it served in wireless
telegraphy will appear in the following pages.
[Illustration: Fig. 188]
XXII
RINGING BELLS AND LIGHTING LAMPS BY ELECTRIC WAVES
[Illustration: Fig. 189]