What appears to be a dark cloud or haze to our eyes is actually made of millions of tiny particles–in this case, not of water, but of burnt matter. There are two kinds of smoke detectors: ionization alarms and photoelectric alarms.
What is RSS? RSS makes it possible to subscribe to a website's updates instead of visiting it by delivering new posts to your RSS reader automatically. Choose to receive some or all of the updates from A Moment of Science: