57 
hy Christian Huygens. 
Horologii pendulo muniti, quod ipse excogitaverat, admodum 
luculenter ac diserte loquitur,” a clock furnished with a pendur- 
lum^ when the letter contains in reality the descr^tion (in Gali- 
leo’s own words) of a free pendulum, a vibrating sector. I 
shall only quote one passage more from the above mentioned 
letter to Bouillau, in which the Prince says, Having seen a 
model constructed by Galileo, differing somewhat from that of 
Huygens in the disposition of the wheels, (in parte deverso 
circa la constitutione della ruote)^'' {Leyden MSS.) ; because 
this (which probably regards Galileo’s son as much as himself^ 
who was blind after 1639,) agrees with what had been written 
to Huygens from Rome in 1660, about a rough sketch of a 
clock attempted by Galileo, and also with the account of the aca- 
demicians del Cimento^ and is besides confirmed in a striking 
manner by Prisi, in his Ehgio del Galilei^ Milan, 1775, where 
he mentions Leopold’s opinion, that Galileo had put nothing in- 
to practice equal to the invention of Huygens, “ as might be seen 
from the little that had been contrived or sketched out by his 
son.” And truly,” he adds himself, the machine of 1649, 
was nothing but slightly sketched {non era che un poco d'^ab^ 
hozzo)."^' He seems to think that the clock represented in the 
experiments of the academicians was made after this model: 
this is not probable, as they are of a much later date. 
After mentioning the concurring testimony of these writers, 
that something had been made or sketched by Galileo or his 
son, I have now the satisfaction of presenting to the class a fac 
simile of the drawing, representing the contrivance in question. 
(See Plate I. Fig. 5. and the Notice at the end of the article). 
It was found by me among the papers relating to Huygens, in 
the Leyden Library : There is written upon it, in Huygen’s 
own hand, Missa a Ser^, Principe Leopoldo ad BuUialdum 
ah illo ad me : R. 15. gan, 1660, cum descriptio mei Horo- 
logii edita fuissetf A"". 1658 ,• and in another hand, which 
I recognise for that of Bouillau, these words, Horloge com- 
mence par Galileo Galilei; and on the reverse by the same, 
d Monsieur Monsieur Christian Huygens de Zulichem d la 
Haye. Among the letters of Bouillau, there is a corresponding 
one of the 9th January 1660: I send you the figure of the 
pendulum-clock begim by Galileo, as it was sent to me from 
Florence; and another of the S9th February. You may keep 
