1 1 2 SECTION PHYSICS. 



made by Galileo for observing with greater ease the satellites of 

 Jupiter, and called by him the " Celatonc" or " Testiera" (for the 

 apparatus resembled a diving-helmet, having telescopes fixed in the 

 apertures for the eyes). It was intended for use on board ship. And 

 speaking of this same instrument, let me mention that towards the 

 end of his life he offered it to Spain at that time an important 

 maritime power, in order that it should be of use for observing the 

 eclipses of Jupiter's satellites, and hence, by knowing the ephemeris, 

 to determine the longitude of any place even in a rough sea. The 

 negotiations, however, with Spain having failed about the year 1636, 

 Galileo offered the same instrument to the States-General of Holland, 

 at the same time stating distinctly the four conditions on which the 

 value of his instrument depended namely, to know the theory and 

 the tables of the " Stelle Medicee," to have perfect telescopes, to 

 overcome the difficulties of the ship's motion, to have a perfect 

 instrument for the measurement of time : all of which conditions he 

 affirmed to be able completely to satisfy, for he had indeed invented 

 a perfect measurer of time ; and as to the motion of the ship, after 

 having devised several other ingenious methods to protect the observer, 

 the idea struck him of placing him in a boat floating in another boat 

 filled with water, a spring being placed between them so that the two 

 boats should not dash against one another. When the transaction 

 which had been delayed through the death of the appointed agents, 

 seemed, at last, to be coming to an agreement, Galileo himself died. 



Allow me, after having spoken of these instruments of Galileo, tho 

 only ones which remain to us, and which I have the good fortune to 

 be able to show you, to call to mind the principal discoveries which 

 he made and afterwards published. And first of all the observation 

 of the spots on the sun. Before he had given up his professorship at 

 Padua, he had occasion while at Venice to point them out to Fra 

 Paolo Sarpi, the celebrated Venetian theologian, and also to Fra 

 Fulgenzio, his disciple and successor. Here is what the latter writes 

 to Galileo, in a letter of the 27th of September, 1621, with reference 

 to the Jesuit, Father Scheiner, who gave himself out as the discoverer 

 of the solar spots : " It seems to me that that German Jesuit is a man 

 of good judgment and deserves high praise ; for as it is their 

 peculiarity to make themselves a name by evil speaking, he could 



