According to "The Story of Gliding" by Ann Welch (chapter 10 - First
Thermals):

"However, the first real thermal soaring, without either hills or
thunderstorms, took place in the United States. An American, A.
Haller, and a German far from home, Wolf Hirth, were the first to
realise their opportunity."

That was the 5th of October, 1930 - almost just over years *after*
Robert Kronfeld's soaring flight from the Wasserkuppe. Also, according
to Simons, once Kronfeld had made the first thermal flight at the
August, 1928 meeting the secret was out and several other pilots made
thermal flights at the same meeting despite not having varios, such as
a 775 m height gain and a 35 km xc goal flight. They'd twigged that
the cumulus was the key.

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Good information. From this it appears that between 1928 and 1930, Kronfeld
and Hirth were the first to "discover" thermals as a useful means of
sustained flight, and experimented with the basic circling techniques we use
today.

In Martin Gregorie's post I noted the adaptation of a variometer originally
used in Zeppelins. Was this the first vario for gliders?

I'm assuming the original development of varios for ridged airships was to
give the crew rising and falling airmass readouts so that they could
correctly trim and shift ballast to keep the ship relatively stable.

I remember reading a story about either the U.S.S Shennandoah or the Macon
traversing the southwest U.S. one day. They had a bad time of it as dessert
thermals caused the airship to practically stand on its tale, causing mayhem
inside the gondola.

Thanks for the good answers to my posting.

Bob