Assertion: telescope's observation | /r/MadeOf | same instrument
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Source sentences:
text: With one of these: an objective diameter of 2.24 inches (57 mm) and a 12 ft (3.7 m) focal length, he discovered the brightest of Saturn's satellites (Titan) in 1655; in 1659, he published his "Systema Saturnium" which, for the first time, gave a true explanation of Saturn's ring—founded on observations made with the same instrument.