De Magnetica [...] Plantarum p. 647

the sun's attraction will easily rotate along with it the face of the flower turned toward the face of the sun, since there would be no resistance from the stem which could distract it from that attraction. To achieve success the matter requires diligent and skilful craftsmanship; I myself have attempted the work with the greatest success; only the following difficulties prevented the perfection of the work; the machine would not tolerate a glass case, but in the open air it was easily displaced from its position by a small disturbance of the air; otherwise, when the sky was quiet, I found that it showed the hours correctly just like a sundial; though when the sun waned it too lagged a bit, as if shrivelled and tired and wanting a rest; added to this, a clock of this sort can hardly last a month, even if cared for with the greatest diligence - so nothing is perfect in every way. While therefore I was trying by assiduous investigation to meet such difficulties and struggling to to bring this sort of experiment to some kind of perfection and solidity, in the year 1633 in Marseille, guided by I know not what Providence, I came across an Arab merchant with whom I conversed a bit about various matters concerning Arabia and the Red Sea; when it came near time to go home and I talked of exploring the time with my hour-ring, he seemed to take a singular pleasure from the use of such a convenient and expeditious clock; so I asked him something about the timepieces customary in Arabia; he replied with considerable knowledge, saying that astronomers used various instruments to investigate the time, and that among others there was a famous Medic who could determine the time night or day with the help of a material which constantly turns toward the sun, and that he not only knew such a material but actually carried it with him among his aromatic merchandise, and was prepared to exchange some of that material for that ring. No sooner said than done; I took the material and gave him the ring; and first at Aix-en-Provence and then at Avignon I made repeated trial of the matter, and found it more true than I had expected.

For that heliotropic material, either in water or balanced magnetically over water, was observed to follow the sun inseparably even when enclosed by glass shutters, from which I gathered that this motion was not due to primary qualities but to a specific force, and that it turned to the sun through similarity of its whole substance, as if to its preserver. I later demonstrated this experiment in Rome by two methods in the presence of the most eminent men, then to others of our Society, then to the most learned outsiders, and not without admiration. The first method was on the surface of water, the second in the middle of the water, more or less in the way that