ON INSTRUMENTS FROM ITAL V. 133 



vibrations of which were perfectly equal. Signer Borelli and Signer 

 Ricci stood at the end, with the youth De' Galilei, who seemed to 

 behave well ; and I was placed in the middle, together with Monsu 

 Filippo d' Augusta, clockmaker to his Highness. When night had 

 come on Signer Borelli made the first sign to the bombardier with the 

 rocket, and then the firing began, but no shot was fired without a sign 

 being given from another rocket. Each one of us was consequently 

 previously warned on each occasion to watch the movement of the flame 

 of the maschio, and we immediately set to work to count the vibrations 

 of our pendulum ; and the others further off did likewise. As many as 

 fifteen shots were fired, and we always found, to my very great satis- 

 faction, the same number of vibrations from the appearance of the light 

 to the arrival of the sound, and ours were always less than eight, and 

 we settled among ourselves that it might be called seven and a half. 

 We finished the experiment at about two and a half o'clock in the 

 night ; and we, who were nearer Florence, remained waiting with the 

 greatest anxiety for the others with the carriage, in order to hear their 

 number of vibrations ; and finally, not to keep you- any longer in sus- 

 pense, they, without knowing what ours had been, told us that they had 

 always counted fifteen and a half ; which was exactly double our time, 

 just as one and one-fifth of a mile is double three-fifths of a mile ; and 

 so we all got into the carriage with the utmost satisfaction and entered 

 Florence about four o'clock at night, and we immediately informed his 

 Highness, who was awake, and expecting the news of the result of our 

 experiment ; and you can imagine with what pleasure he heard our 

 communications. The following evening we repeated the firing from 

 the Petraja, when there was a strong north wind blowing, and yet we 

 found the same result as the previous evenings, which had been 

 forty-one vibrations of the same pendulum. And to put a seal to this 

 story, I must add that I have made the following calculation : If 

 sound traverses 3600 braccia in fifteen-and-a-half vibrations, how 

 many braccia will it have traversed in forty-one vibrations the num- 

 ber between the Palace and the Petraja ? and the fourth number is 

 9522 braccia, which is about the figure given by the greater number of 

 instruments." 



When the Accademia del Cimento afterwards repeated these same 

 experiments, it was found that in five seconds sound traverses one 



