Click here to go to the applet.
This java applet is a simulation that demonstrates
electromagnetic waves in two dimensions.
When the applet starts up you will see a
line (called the "source") emitting red and green plane
waves. The color indicates the magnetic field;
green areas are positive (towards you) and the red areas are
negative (away from you). (In this applet, the magnetic field is
always perpendicular to the plane of the screen.)
In addition to the red and green color, you will see arrows which
indicate the direction of the electric field (which is always in the
plane of the screen).
Conductors will show up as gray. They may also show yellow or white arrows,
indicating current, and a yellow or blue color,
indicating charge. (Yellow means positive charge, and blue means
negative charge.)
These are electromagnetic waves, so in real life they would
be moving at the speed of light.
This is the TE version of the applet. There is also a
TM version.
The Setup popup can be used to view some interesting
pre-defined experiments. Once an experiment is selected,
you may modify it all you want. The choices are:
- Plane Wave: this demonstrates a simple plane wave source.
- Intersecting Planes: this demonstrates two plane waves intersecting
at right angles.
- Reflection At Conductor: this shows wave packets being
reflected by a perfect conductor.
- Oscillating Dipole: this shows an oscillating electric dipole
radiator.
- Half Wave Antenna: this shows a linear antenna whose length is
equal to half the wavelength of the radiation it is emitting.
- Full Wave Antenna (End-Driven): this shows a linear antenna whose
length is
equal to the wavelength of the radiation it is emitting. It is driven at
one end (the yellow end).
- Full Wave Antenna (Center-Driven): this shows a linear antenna whose
length is
equal to the wavelength of the radiation it is emitting. It is driven in
the center.
- Current Loop: this shows a loop of wire with an oscillating
current.
- Big TE01 Mode: this creates a small perfectly conducting cavity
with a standing wave inside it. The electric field is 90 degrees out
of phase with the magnetic field. The field in the cavity is oscillating in
its TE01 mode.
- Big TE10 Mode: this creates a small cavity with a TE10 mode.
- Big TE10+TE01 Mode: this creates a small cavity with TE10
and TE01 modes superposed.
- Big TE10+TE01i Mode: this creates a small cavity with TE10 mode
and TE01 modes superposed out of phase.
- Big TE11 Mode: this creates a small cavity with a TE11 mode.
- TE10 Modes: this creates a set of small superconducting cavities
with TE10 standing waves inside them.
- TEn0 Modes: this creates a set of small superconducting cavities
with TE10, TE20, TE30, and TE40 standing waves inside them. (If the
resolution is set higher then more cavities are present with higher modes.)
- TEn1 Modes: this creates a set of small superconducting cavities
with TE11 and TE21 standing waves.
- TEnn Modes: this creates a set of small superconducting cavities
with various TE modes inside them.
- Waveguides:
This creates a series of waveguides of different widths.
- Capacitor: this shows a small cavity with a capacitor connecting
the two sides.
- Resonant Cavities 1:
This creates a series of rectangular cavities being driven by
a plane wave from above. As you change the frequency you will
see the response of each cavity change. Each cavity has a different
resonant frequency so it will respond differently. After changing
the frequency you may want to wait a bit for things to settle down
(or turn the simulation speed way up).
- Single Slit: this demonstrates diffraction of waves
travelling through a slit.
- Double Slit: this demonstrates diffraction of waves
travelling through a double slit.
- Triple Slit.
- Obstacle: this demonstrates diffraction of waves
travelling around an obstacle.
- Half Plane: this demonstrates diffraction of waves
around the edge of a plane.
- Lloyd's Mirror:
This shows an interferometer which consists of a point source
close to a mirror (at the bottom of the window).
The waves coming from the source interfere with the waves coming
from its mirror image.
The Source popup controls the wave sources (oscillating
currents). It has the
following settings:
-
No Sources: there will be no sources of wave motion.
- 1 Plane Src: there will be a single plane source of waves. The
source consists of an oscillating current that does not vary along the
length of the source. The
ends of the plane source can be dragged anywhere on the screen with the
mouse.
- 2 Plane Src: there will be two plane sources.
- 1 Plane Src (Packets): the plane source will emit wave packets
periodically.
- 1 Antenna Src: there will be a single antenna emitting waves.
The antenna is driven at the yellow end. The current at the white end
is zero.
- 2 Antenna Src: there will be two antennas emitting waves.
- 1 Loop Src: there will be a current loop emitting waves.
- 1 Loop Src (Packets): there will be a current loop emitting wave
packets periodically.
The Mouse popup controls what happens when the mouse is
clicked. The following settings are possible:
- Mouse = Add Perf. Conductor:
Clicking on a
point will create a perfect conductor there. Clicking on
an existing conductor will erase it.
- Mouse = Clear:
Clicking on a point will remove whatever is there.
The Show popup determines which fields or other quantities to
display, and how to display them.
- Show Electric Field (E): Show the electric field as arrows.
- Show E lines: Show the electric field as lines. The
color of the lines go from dark green to light green and
then to white as the field gets stronger. The density of the
lines is kept fairly constant, so in order to determine the
field strength you need to look at the color of the lines
rather than how far apart they are.
- Show Magnetic Field (B): Show the magnetic field
as green (positive, toward you) or red (negative, away from you).
- Show Current (rho): Show the charge density as
yellow (positive) or blue (negative).
- Show Current (j): Show the current density as arrows.
- Show E/B: Show both the electric field arrows and the
magnetic field.
- Show E lines/B: Show both electric field lines and the
magnetic field.
- Show E/B/rho/j: In space, show both the electric field arrows
and the magnetic field;
in conductors, show the current density and charge.
- Show E lines/B/rho/j: In space, show both the electric field lines
and the magnetic field;
in conductors, show the current density and charge.
- Show E/rho: Show the electric field and charge.
- Show E lines/rho: Show the electric field lines and charge.
- Show E/B/j: Show the electric field, magnetic field, and current.
- Show E lines/B/j: Show the electric field lines, magnetic field, and current.
- Show Poynting Vector: Show the Poynting vector, which
indicates the direction of energy transfer. For waves, it
is in the direction of wave motion.
- Show Energy Density: Show the energy density as
shades of yellow.
- Show Poynting/Energy: Show both the energy density and
the Poynting vector.
- Show Disp Current: Show the displacement current.
- Show Disp + j: Show the displacement and conduction
currents.
- Show Disp + j/B: Show the displacement and conduction
currents and magnetic field.
The Clear Fields button magically clears out any fields but does not
remove any currents, sources, or materials. The Clear All button
clears out everything.
The Stopped checkbox stops the applet, in case you want to
take a closer look at something, or if you want to work on something
with the mouse without worrying about it changing out from under you.
The Simulation Speed slider controls how far the waves move
between frames. If you slide this to the left, the applet will go
faster but the motion will be choppier.
The Resolution slider allows you to speed up or slow down the
applet by adjusting the resolution; a higher resolution is slower
but looks better.
The Brightness slider controls the brightness, just like on a
TV set. This can be used to view faint waves more easily.
The E Field Brightness slider controls the relative brightness of the
electric field.
Click here to go to the applet.
java@falstad.com
A far higher place must be assigned to Judaism among the competitors for the allegiance of Europe. The cosmopolitan importance at one time assumed by this religion has been considerably obscured, owing to the subsequent devolution of its part to Christianity. It is, however, by no means impossible that, but for the diversion created by the Gospel, and the disastrous consequences of their revolt against Rome, the Jews might have won the world to a purified form of their own monotheism. A few significant circumstances are recorded showing how much influence they had acquired, even in Rome, before the first preaching of Christianity. The first of these is to be found in Cicero’s defence of Flaccus. The latter was accused of appropriating part of the annual contributions sent to the temple at Jerusalem; and, in dealing with this charge, Cicero speaks of the Jews, who were naturally prejudiced against his client, as a powerful faction the hostility of which he is anxious not to provoke.330 Some twenty years later, a great advance has been made. Not only must the material interests of the Jews be respected, but a certain conformity to their religious prescriptions is considered a mark of good breeding, In one of his most amusing satires, Horace tells us how, being anxious to shake off a bore, he appeals for help to his friend Aristius Fuscus, and reminds him of217 some private business which they had to discuss together. Fuscus sees his object, and being mischievously determined to defeat it, answers: ‘Yes, I remember perfectly, but we must wait for some better opportunity; this is the thirtieth Sabbath, do you wish to insult the circumcised Jews?’ ‘I have no scruples on that point,‘ replies the impatient poet. ‘But I have,’ rejoins Fuscus,—‘a little weak-minded, one of the many, you know—excuse me, another time.‘331 Nor were the Jews content with the countenance thus freely accorded them. The same poet elsewhere intimates that whenever they found themselves in a majority, they took advantage of their superior strength to make proselytes by force.’332 And they pursued the good work to such purpose that a couple of generations later we find Seneca bitterly complaining that the vanquished had given laws to the victors, and that the customs of this abominable race were established over the whole earth.333 Evidence to the same effect is given by Philo Judaeus and Josephus, who inform us that the Jewish laws and customs were admired, imitated, and obeyed over the whole earth.334 Such assertions might be suspected of exaggeration, were they not, to a certain extent, confirmed by the references already quoted, to which others of the same kind may be added from later writers showing that it was a common practice among the Romans to abstain from work on the Sabbath, and even to celebrate it by praying, fasting, and lighting lamps, to visit the synagogues, to study the law of Moses, and to pay the yearly contribution of two drachmas to the temple at Jerusalem.335 Jeff’s hand was quietly coming down. “What happened to you?” begged Sandy. “Something new has come up, sir. I was waiting there by my ship a good while back, and I heard another one cruising and spiraling, shooting the field, I guess, because he came in and set down. My crate, just the way you ordered, was down by the grove, not in plain sight in the middle of the course. But Jeff set his ship down, left the engine running, and went off. I stayed hid to see what would happen, but when he didn’t come back, I thought I’d better go and find you—and see if it meant anything to you.” She stood alone, with the sticky, wet knife in her hand, catching her breath, coming out of the madness. Then she stooped, and pushing the branches aside felt about for her pistol. It lay at the root of a tree, and[Pg 80] when she had picked it up and put it back in the holster, there occurred to her for the first time the thought that the shot in the dead stillness must have roused the camp. And now she was sincerely frightened. If she were found here, it would be more than disagreeable for Landor. They must not find her. She started at a swift, long-limbed run, making a wide detour, to avoid the sentries, bending low, and flying silently among the bushes and across the shadowy sands. The year 1756 opened with menaces to England of the most serious nature. The imbecility of the Ministry was beginning to tell in the neglect of its colonies and its defences. France threatened to invade us, and a navy of fifty thousand men was suddenly voted, and an army of thirty-four thousand two hundred and sixty-three of native troops; but as these were not ready, it was agreed to bring over eight thousand Hessians and Hanoverians. To pay for all this it was necessary to grant excessive supplies, and lay on new duties and taxes. In presenting the money bills in the month of May, Speaker Onslow could not avoid remarking that there were two circumstances which tended to create alarm—foreign subsidies and foreign troops introduced, and nothing but their confidence in his Majesty could allay their fears, or give them confidence that their burdens would be soon reduced. There was, in fact, no chance for any such reduction, for wars, troubles, and disgraces were gathering around from various quarters. The first reverse came from the Mediterranean. MUCH to their amazement, the boys waked up the next morning in Nashville, and found that they had passed through the "dark and bloody ground" of Kentucky absolutely without adventure. After drawing and dividing the rations and cartridges. Si gave the boys the necessary instruction about having their things ready so that they could get them in the dark the next morning, and ordered them to disregard the bonfires and mirth-making, and lie down to get all the sleep they could, in preparation for the hard work of the next day. Then, like the rest of the experienced men, who saw that the campaign was at length really on, and this would be the last opportunity for an indefinite while to write, he sat down to write short letters to his mother and to Annabel. "Bully for the Wild Wanderers of the Wabash," Shorty joined in. "They're the boss regiment in the army o' the Cumberland, and the Army o' the Cumberland's the boss army on earth. Hooray for US Co. Le's have a speech. Where's Monty Scruggs?" "Bring a light, do—I can't abide this dark." Albert suddenly began to look uneasy. After all he was not really drunk, only a little fuddled. He walked straight, and his roll was natural to him, while though he was exceedingly cheerful, and often burst into song, his words were not jumbled, and he generally seemed to have a fair idea of what he was saying. "But I heard what the doctor said to you." "A purty accident—wud them stacks no more dry than a ditch. 'Twas a clear case of 'bustion—fireman said so to me; as wicked and tedious a bit o' wark as ever I met in my life." Calverley stept from the shadow of the cliff, and beheld a meteor in the sky, brightening and expanding, as the clouds opened, until it assumed the appearance of a brilliant star, of astonishing magnitude, encircled by dazzling rays, which, in a singular manner, were all inclined in one direction, and pointing to that part of the horizon where lay the rival of England—France. The foreman's face assumed a deeper hue than usual: he looked fiercely at the galleyman, but there was a determination in the weather-beaten face that made him pause ere he spoke. "Galleyman," he at length said, "you knew the business before you came: if you be so fond of saving old witches' lives, why didn't you say so, that I might not now be in this dilemma?" "No, no, not the boy," replied Merritt, rather impatiently.