FREE BALLOON IN CLOSE PROX TO ACFT.

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CRUISING WBOUND FROM CMH TO CPS AT FL230; WAITING FOR CLRNC TO CLB TO CRUISING ALT. SAW BALLOON GO BY L SIDE AND SLIGHTLY BELOW US. BALLOON WAS YELLOWISH ORANGE IN COLOR WITH WHAT APPEARED TO BE A CABLE AND A SMALL PAYLOAD ATTACHED TO IT. ATC PROVIDED NO WARNING; AND ACKNOWLEDGED OUR RPT WITH A 'ROGER' AND A FREQ CHANGE. I WOULD GUESS THAT GIVEN OUR CRUISE TRUE AIRSPD OF OVER 450 KTS; THAT A COLLISION WITH SUCH A BALLOON COULD DEFINITELY INFLICT SOME DAMAGE TO SAY THE LEAST. IT IS MY UNDERSTANDING THAT ATC IS SUPPOSED TO BE AWARE OF THESE THINGS (FAR 101.37) AND PROVIDE ADVISORIES AS APPROPRIATE (ATC 9-8-1). IN MY 17 YRS AND NEARLY 10000 HRS OF FLYING; I DON'T THINK I'VE EVER HEARD A RPT OF THESE BALLOONS. IN FACT; I NEARLY HIT ANOTHER ONE AT FL450 OVER NORTHERN FLORIDA IN 1987. PERHAPS THIS COULD EXPLAIN SOME OF THE ACCIDENTS WHERE A PERFECTLY NORMAL FLT DISAPPEARS OFF THE RADAR SCOPE AND GOES STRAIGHT IN FOR NO APPARENT REASON. I DON'T KNOW; AND THESE THINGS SCARE ME BECAUSE AT HIGH SPDS AND EVEN IF YOU'RE REALLY LOOKING HARD; YOU WON'T SEE IT UNTIL IT'S TOO LATE TO DO MUCH ABOUT IT.