INTEREST in the complex structure of the important lines in the arc spectrum of mercury has been revived by the suggestion of Nagaoka, Sugiura, and Mishima (NATURE, March 29, 1924) that the ...

To help locate where a place is in the world, people use imaginary lines called latitude and longitude. Find out more with this year 3/4 BBC Bitesize geography guide.

Used together, the lines served as a “frame of reference.” If pigeons, he reasoned, are sensitive to some factor connected with the lines of latitude, they have all they need to find their way ...