John Dalton used circles to represent atoms in his atomic theory. He used different sizes and colors of circles to differentiate between different elements.

Here's how his symbols worked:

* Color and Size: Each element had a unique color and size for its circle.

* Simple Circles: Dalton used simple circles, not the complex symbols we use today.

* Combinations: He showed compounds by combining the circles of different elements. For example, water would be represented by one small circle (hydrogen) and one larger circle (oxygen).

Example:

* Hydrogen: Small white circle

* Oxygen: Large black circle

* Water: One small white circle and one larger black circle

Dalton's symbols, though simple, were a groundbreaking step in understanding the basic building blocks of matter.