multiple photo galleries in html/css - html

Question

I am trying to create multiple photo galleries on one page. I can get the first gallery to work but when I try to add a second gallery neither of the pictures work. Could someone help me out and see what I have wrong or am missing? Thank you!
HTML:
<div class="gallery" align="center" id="gal1" >
<div class="thumbnails" id="thumb1" >
<img onmouseover="preview1.src=img1.src" name="img1" src="flower.jpg" alt="" />
<img onmouseover="preview1.src=img2.src" name="img2" src="blue_light.jpg" alt="" />
<img onmouseover="preview1.src=img3.src" name="img3" src="paintwithlight/JPEG/yellow-blue.jpg" alt="" />
<img onmouseover="preview1.src=img4.src" name="img4" src="paintwithlight/JPEG/abstract.jpg" alt="" />
<img onmouseover="preview1.src=img5.src" name="img5" src="paintwithlight/JPEG/angelin.jpg" alt="" />
<img onmouseover="preview1.src=img6.src" name="img6" src="paintwithlight/JPEG/anna.jpg" alt="" />
<img onmouseover="preview1.src=img7.src" name="img7" src="paintwithlight/JPEG/butterfly.jpg" alt="" />
<img onmouseover="preview1.src=img8.src" name="img8" src="paintwithlight/JPEG/clash.jpg" alt="" />
<img onmouseover="preview1.src=img9.src" name="img9" src="paintwithlight/JPEG/craze.jpg" alt="" />
<img onmouseover="preview1.src=img10.src" name="img10" src="paintwithlight/JPEG/dolphin.jpg" alt="" />
<img onmouseover="preview1.src=img11.src" name="img11" src="paintwithlight/JPEG/greenswirl.jpg" alt="" />
<img onmouseover="preview1.src=img12.src" name="img12" src="paintwithlight/JPEG/halfcircle.jpg" alt="" />
<img onmouseover="preview1.src=img13.src" name="img13" src="paintwithlight/JPEG/mindblown.jpg" alt="" />
<img onmouseover="preview1.src=img14.src" name="img14" src="paintwithlight/JPEG/mystic.jpg" alt="" />
<img onmouseover="preview1.src=img15.src" name="img15" src="paintwithlight/JPEG/radiation.jpg" alt="" />
<img onmouseover="preview1.src=img16.src" name="img16" src="paintwithlight/JPEG/rainbow.jpg" alt="" />
<img onmouseover="preview1.src=img17.src" name="img17" src="paintwithlight/JPEG/stuckcircle.jpg" alt="" />
<img onmouseover="preview1.src=img18.src" name="img18" src="paintwithlight/JPEG/swirl.jpg" alt="" />
<img onmouseover="preview1.src=img19.src" name="img19" src="paintwithlight/JPEG/whitelight.jpg" alt="" />
<img onmouseover="preview1.src=img20.src" name="img20" src="paintwithlight/JPEG/zeus.jpg" alt="" />
</div>
<div class="preview1" align="center">
<img name="preview1" src="flower.jpg" alt=""/>
</div>
</div>
<div class="gallery" align="center" id="gal2" >
<div class="thumbnails" id="thumb2" >
<img onmouseover="preview2.src=img1.src" name="img1" src="nature/JPEG/apple.jpg" alt="" />
<img onmouseover="preview2.src=img2.src" name="img2" src="nature/JPEG/cig.jpg" alt="" />
<img onmouseover="preview2.src=img3.src" name="img3" src="nature/JPEG/deadflower.jpg" alt="" />
<img onmouseover="preview2.src=img4.src" name="img4" src="nature/JPEG/halfnhalf.jpg" alt="" />
<img onmouseover="preview2.src=img5.src" name="img5" src="nature/JPEG/leaf.jpg" alt="" />
<img onmouseover="preview2.src=img6.src" name="img6" src="nature/JPEG/liveflower.jpg" alt="" />
<img onmouseover="preview2.src=img7.src" name="img7" src="nature/JPEG/mush.jpg" alt="" />
<img onmouseover="preview2.src=img8.src" name="img8" src="nature/JPEG/mushroom.jpg" alt="" />
<img onmouseover="preview2.src=img9.src" name="img9" src="nature/JPEG/pumpkin.jpg" alt="" />
<img onmouseover="preview2.src=img10.src" name="img10" src="nature/JPEG/redflower.jpg" alt="" />
<img onmouseover="preview2.src=img11.src" name="img11" src="nature/JPEG/rocks.jpg" alt="" />
<img onmouseover="preview2.src=img12.src" name="img12" src="nature/JPEG/silo.jpg" alt="" />
<img onmouseover="preview2.src=img13.src" name="img13" src="nature/JPEG/tree.jpg" alt="" />
<img onmouseover="preview2.src=img14.src" name="img14" src="nature/JPEG/tree2.jpg" alt="" />
<img onmouseover="preview2.src=img15.src" name="img15" src="nature/JPEG/tree3.jpg" alt="" />
<img onmouseover="preview2.src=img16.src" name="img16" src="nature/JPEG/water.jpg" alt="" />
<img onmouseover="preview2.src=img17.src" name="img17" src="nature/JPEG/yellowflower.jpg" alt="" />
</div>
<div class="preview" align="center">
<img name="preview2" src="nature/JPEG/apple.jpg" alt=""/>
</div>
</div>
CSS:
.thumbnails img {
height: 80px;
border: 4px solid #555;
padding: 1px;
margin: 0 10px 10px 0;
}
.thumbnails img:hover {
border: 4px solid #00ccff;
cursor:pointer;
}
.preview1 img {
border: 4px solid #444;
padding: 1px;
width: 800px;
}
.thumbnails #thumb2 img {
height: 80px;
border: 4px solid #555;
padding: 1px;
margin: 0 10px 10px 0;
}
.thumbnails #thumb2 img:hover {
border: 4px solid #00ccff;
cursor:pointer;
}
.preview2 img {
border: 4px solid #444;
padding: 1px;
width: 800px;
}

Answer 1

The name attribute on an <img> tag is obsolete in HTML5 and should not be used in production.
→ Use data-* attribute instead.
align attribute is obsolete or nonstandard
→ Use style text-align:center; instead
Inline JavaScript makes developing hard and code maintenance a nightmare.
→ Place your JavaScript code into <script>, away from your HTML tags.
Here's an example how to easily create multiple hover-able galleries:
function hoverGal() {
var bigID = this.parentNode.dataset.targetid;
document.getElementById(bigID).src = this.dataset.big;
}
[].forEach.call(document.querySelectorAll("[data-big]"), function(thumb) {
thumb.addEventListener("mouseenter", hoverGal, false);
});
<div data-targetid="big1">
<img src="//placehold.it/100x60/0fb" data-big="//placehold.it/360x200/0fb" alt="">
<img src="//placehold.it/100x60/fb0" data-big="//placehold.it/360x200/fb0" alt="">
<img src="//placehold.it/100x60/b0f" data-big="//placehold.it/360x200/b0f" alt="">
</div>
<img id="big1" src="//placehold.it/360x200/0fb">
<div data-targetid="big2">
<img src="//placehold.it/100x60/bf0" data-big="//placehold.it/360x200/bf0" alt="">
<img src="//placehold.it/100x60/f0b" data-big="//placehold.it/360x200/f0b" alt="">
<img src="//placehold.it/100x60/0bf" data-big="//placehold.it/360x200/0bf" alt="">
</div>
<img id="big2" src="//placehold.it/360x200/bf0">
That way you won't get into collision having duplicate thumbnails names / IDs or having to invent tons of different names.