the secrets of the movements of the heavens, of the stars, of 

 the planets and of the waters. "I have discovered," he wrote, 

 "why the earth floats in the air, why the waters make a 

 circle around the earth, and why all things except fire tend 

 towards the centre of the earth ; I have discovered the causes 

 of thunder, lightning, rain, wind and the tides." And he 

 offered to show the King proof of his discovery of "Primi 

 mobilis" in the shape of a ball that revolved every twenty- 

 four hours, and would continue to do so for a thousand years ; 

 and he referred to other instruments "made with weights, 

 springs, running waters, wind and fire that would move per- 

 petually, without expense, and furnish much power." It was 

 | a report of this letter that aroused the interest of Rudolph. 



Drebbel has also been credited with the invention of the 

 thermometer, but this is a mistake based upon faulty inter- 

 pretation of a simple experiment described by him 'in a treatise 

 on the "Elements," published in Dutch in 1608. This ex- 

 periment was the heating of an empty retort, the neck of 

 which was plunged under water, and observing the bubbles 

 rising due to the expansion of the air within the heated vessel ; 

 he did not even use the phenomenon as a thermoscope. Drebbel, 

 however, is said to have discovered the beautiful carmine- 

 lake formed by the action of tin-salts on cochineal. 



After Drebbel's arrival in Prague, Rudolph soon found 

 that the perpetuum mobile was useless, though he did not 

 believe it fallacious, and in one of his ill-tempered moods he 

 ordered the imprisonment of the unlucky inventor. From his 

 dungeon Drebbel wrote a pleading letter to the Emperor 

 begging for freedom and promising to show him a remark- 

 able musical instrument described in these words: 



"As soon as the sun shines the curtains hanging before 

 the Clavicymbal will be withdrawn automatically and the 

 sweetest of music will be heard ; when the sun sets or goes 



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