104 SECTION PHYSICS. 



ranean places, that in winter seem to our senses warmer than in 

 summer, are at all times at the same temperature. And we are, there- 

 fore, compelled to say that the apparent difference comes from the way 

 in which the air which circulates there affects our senses, and not from 

 any variation in the degree of heat or of cold in the place. 



Fra Paolo Sarpi, in a letter to Galileo Galilei, dated the nth of 

 September, 1602, says, that the same year Galileo had carefully ex- 

 amined the work of Guglielmo Gilberto, published in 1600 : " De 

 Magnete, &c.," and had repeated the experiments mentioned in it, and 

 also made many new ones. The principal result to which he came 

 was that of discovering the way to multiply the attractive power of 

 magnets by arming them in a special manner. From a letter of 

 Galileo himself, addressed to the Secretary of State, Curzio Pichena, 

 we learn that he (Galileo) considered it probable that the same piece 

 of loadstone did not preserve an equal power in all places on our 

 globe. He states, moreover, that he was engaged in making the 

 magnet bear three times its own weight ; and that by dividing it into- 

 pieces, he could render it capable of raising thirty or forty times its 

 own weight ; finally he observes that the longer a magnet sustains a 

 weight, the more it gains in strength. In another letter, to Marsili, 

 Galileo announces that he had succeeded in making a magnet six 

 ounces in weight bear 150 ounces. And the Abbot Castelli, in his 

 lecture on the magnet, says : " I have seen a loadstone, only six ounces 

 in weight, armed with iron by the untiring industry of Sig. Galileo 

 and presented to his Serene Highness the Grand Duke Ferdinand, 

 which lifts fifteen pounds of iron, worked into the shape of a sepulchre." 1 

 Here is this historical magnet. As to the form of a sepulchre, this 

 shape was probably given to illustrate the legend of Mahomet's tomb 

 remaining suspended in the air. 



And now, approaching the subject of Galileo's telescope, I cannot 

 pass over in silence the fact that the invention of spectacles is likewise 

 due to a Florentine. Ferdinando Leopoldo del Migliore, in his work 

 printed in 1684, and entitled " Firenze citta Nobilissima Illustrata," 

 writes as follows : " There was a memorial (in Santa Maria del Fiore) 

 which came to grief at the restoration of that church ; it was, however, 

 duly inscribed in our ancient register of burials, and is all the more 

 dear to us, as it is, thanks to it, that we are made acquainted with the 



