it connects the arm and and the base of the microscope. it also allows one to tilt the microscope so viewing is possible while seated​

I think it is the Body tube (head)

burning of wood and coal

explanation:

the panel also concluded there's a better than 95 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in earth's temperatures over the past 50 years.