GALILEO. 
trochoid, though the properties of it were 
afterwards chiefly demonstrated by his pu- 
pil Torricelli. He invented the simple pen- 
dulum, and made use of it in his astronomi- 
cal experiments : he had also thoughts of 
applying it to clocks, but did not execute 
that design. The glory of that invention 
was reserved for his son Vincenzo, who 
made the experiment at Venice in 1649 ; 
and Huygens afterwards carried the inven- 
tion to perfection. Of Galileo’s invention 
also was the machine with which the Vene- 
tians render their laguna fluid and navi- 
gable. 
“ He also discovered the gravity of the air, 
and endeavoured to compare it with that of 
water ; and opened several other inqui- 
ries in natural philosophy. He was not es- 
teemed and followed by philosophers only ; 
but was honoured by persons of the greatest 
distinction of all nations. Galileo had scho- 
lars worthy of so great a master, by whom 
the gravitation of the atmosphere was fully 
established, and its varying pressure accu- 
rately and conveniently measured, by the 
column of quicksilver of equal weight sus- 
tained by it in the barometrical tube. The 
elasticity of the air, by which it perpetually 
endeavours to expand itself, and while it 
admits of condensation, resists in propor- 
tion to its density, was a phenomenon of 
a new kind, (the common fluids having 
no such property), and of the utmost impor- 
tance to philosophy. These principles 
opened a vast field of new and useful know- 
ledge, and explained a great variety of phe- 
nomena, which had been accounted for in 
an absurd manner before that time. It 
seemed as if the air, the fluid in which men 
lived from the beginning, had been then 
first discovered. Philosophers were every 
where busy, enquiring into the various pro- 
perties and their effects ; and valuable dis- 
coveries rewarded their industry. Of the 
great number who distinguished themselves 
on this occasion, we cannot but mention 
Torricelli and Viviani, in Italy ; Pascal, in 
France ; Otto Guricke, in Germany ; and 
Boyle, in England.” 
Galileo wrote a number of treatises, of 
which the principal published during his 
life-time : besides bis “ Mechanics,” “ Ba- 
lance,” and “ Dialogues,” already mention- 
ed, were, “ The Operations of the Com- 
pass, geometrical and military,” 1606 ; “ A 
Discourse, addressed to the Most Serene 
Cosmo II. Grand Duke of Tuscany, con- 
cerning the swimming of Bodies upon, and 
tlieir submersion in, Water,” 1612; “Nuncius 
Siderous,” 1610, of which a “Continuation” 
or “ An Essay on the History of Galileo’s 
last Observations on Saturn, Mars, Venus, 
and the Sun, &c.” was afterwards collected 
from letters between Galileo and his cor- 
respondents ; “ A Letter concerning the 
Trepidation of the Moon, lately discovered, 
inscribed to Alphonso Antonini, with Anto- 
nini’s Answer,” 1638 ; “A Discourse of the 
Solar Spots, &c. with Predictions and 
Eph^merides of the Medicean Planets,” 
1613 ; the famous Italian piece, entitled, 
“ II Saggiatore,” written in defence of Gui- 
ducci’s “ Discourse on Comets,” and con- 
taining a complete account of the physiology 
and astronomy of our author, printed in 
1623 ; “A Letter to Prince Leopold of 
Tuscany, examining the fiftieth chapter 
of Licetus’s Letheosphoros “ A Letter 
to Christopher Greinbergerus, concerning 
the Montuosity of the Moon,” 1611 ; “ Ma- 
thematical Discourses and Demonstrations 
concerning two new Sciences, relating to 
Mechanics and local Motions, together with 
an Appendix concerning the Centre of Gra- 
vity in some Solids,” 1638, &c. 
The preceding articles, together with 
some other treatises, written either by Ga- 
lileo, or by some of his disciples, in defence 
of his doctrines and observations, were 
collected and published by Menolessi, in 
1666, under the title of “ L’Opere de Ga- 
lileo Galilei Lynceo, nobile Fiorentino,’’ 
&c. in two volumes quarto. Several of 
these pieces were translated into English, 
and published by Thomas Salisbury, in his 
“ Mathematical Collections,” in two vols. 
folio. 
A volume also of his “ Letters” to seve- 
ral learned men, and solutions of a variety 
of problems, was published at Bologna, in 
quarto. His last disciple Vincenzo Viviani, 
who proved a very eminent mathematician, 
methodised a piece of his master’s, and 
published it under the title of “ Quinta 
Libro de gli Elementi d’ Euclid,” &c. 1674, 
quarto ; and he also published some other 
pieces of Galileo, including extracts from 
his “ Letters to a learned Frenchman,” in 
which the author gives an account of the 
works which he intended to have published, 
and an extract of a letter to John Camillo, 
a mathematician of Naples, concerning the 
angle of contact. Many other of Galileo’s 
writings were unfortunately lost to the 
world, owing to the superstition of one of 
his ignorant nephews ; who, considering 
that his uncle died a prisoner of the holy 
office, though permitted to reside in his 
