How to do a hygrometer?

1, material: two wooden boards (100mm×50mm× 10mm and 50mm×20mm× 10mm respectively), a bamboo chopstick, cotton thread, small nails, pins, some salt, and a small semicircular wooden board.

2, tools: scissors, small hammer.

3, production method: according to the figure, use glue or nails to make two wooden boards and semi-circular wooden boards into a column frame. Nail a bamboo chopstick horizontally at the upper end of the column (chopsticks can rotate around the central nail), and press a needle in the middle of the bamboo chopstick as an indicator. Hang a mass of old cotton at the right end (cotton should be soaked in strong brine first, dried before use), and a small piece of wood with the same weight as cotton at the left end. Adjust the binding distance so that the chopsticks are horizontal and the indicator is vertically centered. The words "sunny" and "cloudy" are written on the left and right sides of the semicircular plate respectively. A simple hygrometer was made.

4. Tips: On rainy days, the humidity in the air increases. Cotton soaked in salt water absorbed the moisture in the air, and its weight increased. The right end of chopsticks is inclined downward, and the pointer is inclined to the right, pointing to the word "Yin". On the contrary, when the weather is clear and the air is dry, the cotton ball becomes lighter and the pointer leans to the left, pointing to the word "sunny".