SIO M. Van Swinden o?? the Invention of Pendulum-Clochs 
gens neither had nor could have the least knowledge of it. 
This, I. believe, will show Galileo to have accomplished even 
something more than what his most zealous defenders have 
^ . ’1 
brought forward to this day. 
Fourthly^ By proving the narrative respecting Trefler in 
Becker’s work to be greatly exaggerated, and that the most 
probable circumstances in it must, from their very nature, have 
been unknown to Huygens. 
And, lastly y By explaining the origin of those pretended 
pendulum-clocks employed, it is said, by Tycho Brahe, whose 
death had taken place more than thirty years before any thing 
respecting Galileo’s attempts were made known. 
1. With regard to the letters of Galileo to Beau grand, there 
is found but oiie in the quarto edition of his works in Italian of 
1718, dated November 1633, in which, speaking of the longi- 
tude, he mentions the necessity of having accurate clocks, 
(giusto or ologio^) wMith. I construct with so much facility, 
precision and simplicity, that they do not admit of an error of 
a single second, not only in an hour, but even in a day in a 
month.” Whether there be others in the Lettre medite dUommi 
illustrii by Fabroni, I have not been able to ascertain ; but 
they cannot possibly contain more information than those which 
we are next to examine, and which were v/ritten professedly on 
the subject hinted at in the above letter to Beaugrand. 
These are addressed to Beaal, formerly Governor of India, 
a man of great merit, knowledge, and authority in Holland. 
Hortensius, Professor of Mathematics at Amsterdam, the cele- 
brated Grotius, and the States-General, and relate all to the dis- 
covery which Galileo had made of the Satellites of J upiter, their 
eclipses, and his method of finding the longitude by means of 
them. After having applied in vain for the support and coun- 
tenance of the Court of Spain, he resolved, in 1635, to offer 
his discovery to the States-General of the United Provinces. 
This correspondence, which was carried on chiefly through the 
medium of Deodati, at Paris, and Grotius, is contained in his 
works, to which may be added the Epistol^e Grotii. In his 
first communication of March 1636 to the States, he enume- 
rates the requisites for making a good observation at sea, and men- 
tions as one an excellent clock “ {esquisUo orologloj) to count the 
