Convenient circulation is indeed one of the reasons, compared to gold coins, silver coins and copper coins are undoubtedly more suitable for use in daily life.

But this is not the main reason, the reason why the horse whistle needs more silver coins is mainly to realize an invention.

Armed with a thousand brand-new Browning revolvers, and guerrilla warfare mantras taught by the horse whistle, Chaves left Sleeping Bear City......

Ma Whistle took the silver coin, and first found a few bottles of nitric acid to purify the silver in the silver coin.

The silver content of these Spanish dollars is not high, only about 90 percent. Silver coins are generally not pure silver and often need to be added with some other metal, mainly to increase their hardness and make them more durable.

He then gave the purified silver to a blacksmith who instructed him to make silver thread and some small parts.

With these silver wires and parts, Ma Whistle can officially start his invention - the metal detector.

Strictly speaking, he has already invented a metal detector, after all, the principle of this thing is not complicated, it is mainly a eddy current effect, or the content of high school physics, of course he can make it.

But the problem was that the metal detector he had invented before was too poor. In the beginning, it was even necessary to put the metal on it to get a reaction.

It may be that the design is not good enough, or it may be that his craftsmanship is not good.

Of course, it is more likely that the pre-technology is a bit insufficient, the battery is an improved voltaic stack, the voltage is not stable enough, and the indicator device is a small fan, which is not very intuitive.

All in all, no matter how much he improved, the performance of the metal detector was never ideal. So in the end, he planned to change all the wires to silver wires and see if he could improve them again.

After all, silver is the most conductive metal, and although it is not much stronger than copper, it is still worth trying.

Soon after, he would go to California in search of gold, aided by a metal detector, which was much more efficient than the naked eye, even if it was the most rudimentary.

Ma Whistle replaced all the conductive parts of the metal detector with silver, and re-experimented.

The detector was so rudimentary and somewhat bulky, starting with a boxy wooden box containing a voltaic stack.

The wooden case has an opening through which a cowhide-wrapped silver wire protrudes and is attached to the handle, below which is the indicator fan and coil.

The coils and handles are of course mostly protected by a wooden shell, and a glass is fastened to the indicator fan to protect it from outside air movement.

For the average person, a wooden box with a battery may need to be carried on the back, but with the size of a horse whistle, it is enough to carry it in the hand.

In the Chief's Hall, there are some gold coins on the ground.

Carrying the battery box in one hand and the handle in the other, the horse whistle slowly approached the gold coins from a distance while observing the changes in the fan.

Under his careful tuning, the speed of the fan is relatively stable, at least by the standards of the naked eye.

As the metal detector and the gold coin approached, the induced magnetic field generated by the gold coin changed the current in it, and the rotation of the fan also changed, first slower, and then when the horse whistle retracted the detector slightly, the fan speed became faster.

When it is far away from the metal, the fan jumps sideways back and forth between fast and slow.

The accuracy is not bad, but the detection distance is still not far, and it can only detect the metal in front of you.

It seems that this can only be done so far.

At this time, when a rainy day came in from outside, he immediately saw something in the hand of the horse whistle and asked, "What is this?" ”

"Metal detectors." Ma Whistle said, placing the wooden box on the table, then passing the handle over, "Would you like to try it?" ”

Rainy day curiously took the handle: "How to use it?" ”

"Put this close to where you want to probe, and if there's metal there, the speed of the fan will tell you." The horse whistle points to the location of the detector's coil.

"Really?" Surprised by the rainy day, he couldn't wait to pick up the detector and approach the gold coin next to him.

Sure enough, as the whistle said, as soon as the detector approached the gold coin, the fan on it immediately began to slow down.

Around the coin, each change in distance brings about a change in fan speed, and once away from the coin, the fan returns to stability.

"This ...... It's incredible! "I couldn't help but open my eyes on a rainy day, and then I tried it with copper and iron, and found that copper and iron can be found by detectors like copper and iron.

"How?" He flipped the probe over and looked at the silver coil that wasn't wrapped in a wooden shell.

"As you can imagine, I talked a little bit about how it works in a mathematics and science seminar." Ma Whistle said with a smile.

There was a bit of a headache on a rainy day, and apparently he wasn't very good at math and physics: "It's Faraday's...... The Law of Electromagnetic Induction? ”

"Almost." Ma Whistle nodded, "Specifically, this detector applies an effect that I call 'eddy currents'. Of course, others may not be fully aware of this effect. ”

"Including Faraday." He added.

Faraday is still alive, a scientist of great repute.

"Sounds amazing." Rainy Sky touched his chin, "But this thing doesn't seem to have much practical significance, are you going to use it to detect something, iron ore?" ”

Ma Whistle: "It can't detect iron ore, in fact, it can't detect almost any mine." After all, it's a metal detector, not a metal mineral detector – except for the gold mine. ”

"Why?"

Ma Whistle went on to explain: "Because gold is often present in nature as a single substance. ”

Rainy day thought for a moment: "So you're going to use it to find gold mines?" ”

"Hmm...... Neither is it. Ma Whistle thought for a moment, "After all, gold mines are always scarce, and in a place as big as North America, when will this little probe be able to find gold mines?" ”

He was actually there to detect gold mines.

Although the performance of this detector is not very good, it is certain that it is stronger than the naked eye.

The area of detection is not too large, and it should be relatively easy to detect results in the vicinity of Sacramento.

But it is obviously not appropriate to say it directly now, after all, it is so early...... He said that there were gold mines near Sacramento, which inevitably gave people a sense of admiration.

And if you don't designate a relatively small area, it would be silly to use this thing to find gold mines across the continent.

"In that case, what's the use of this thing?" Asked again on a rainy day.

"......" Ma Whistle didn't know how to answer for a while, and finally had to use Faraday's famous quote, "What can a newborn baby do?" ”