Duplex telegraphy consists in the simultaneous transmission of two messages, one in each direction, over the same wire.
If simultaneous, cause is effect and effect cause.
The simultaneous system of two quadratic forms ai, ay, say f and 0, consists of six forms, viz.
The only new problem introduced is the simultaneous transmission of two messages in the same direction; this is sometimes ruplex called " diplex transmission."
Ptolemy knew but of a few latitudes which had been determined by actual observation, while of three longitudes resulting from simultaneous observation of eclipses he unfortunately accepted the least satisfactory, namely, that which placed Arbela 45° to the east of Carthage, while the actual meridian distance only amounts to 34°.