Chair back cushions are buffeted by every wind that blows, and periodic summer rains run from the top of the cushion down, creating a greater opportunity for taking on moisture through the seams, with the resulting risk of mold and mildew.
Numerous attempts have been made to find periodic variations in thunderstorm frequency.
His name is best known for the share he had in the periodic classification of the elements.
In its chemical relations, titanium is generally tetravalent, and occurs in the same sub-group of the periodic classification as zirconium, cerium and thorium.
"Time for our periodic chat, little brother," he said, and motioned to the other chair before the hearth.