Notices of Books . 
fOCtober, 
54 6 
of speCtra. Maps are now drawn to twelve times the scale of 
Angstrom’s map, and of course the mapping has become much 
more minute. Thus in Angstrom’s map only three lines are 
shown between H and H 2 , while in the new maps no less than 
ninety-nine are inserted. 
Mr. H. C. Sorby followed with an account of “ SpeCtrum 
Microscopes and the Measuring Apparatus used with them.” 
Other papers were read — by M. Picket, on “ Ice-making Ma- 
chines on “ Compass Correction in Iron Ships,” by Sir Wm. 
Thomson; “The Radiometer,” by Prof. Wartmann, of Geneva; 
and “ The Anemometer,” by Mr. Fletcher. 
At the second meeting of the Conference Dr. Tyndall described 
some of his remarkable experiments on the reflection of sound 
by layers of air of different densities, and on sensitive flames. 
Dr. Stone read a paper on “Just Intonation ” in music, and on 
the limits of audible sound ; and Mr. Bosanquet gave an account 
of his instruments for the attainment of just intonation. Prof. 
W. G. Adams then read a paper on Sir Charles Wheatstone's 
acoustical discoveries. 
In a very able and detail article on the “ Instruments contri- 
buted by Italy,” Prof. Eccher discussed the various inventions 
and discoveries of Galileo, and the instruments of the Accademia 
del Cimento, so liberally contributed to the Loan Collection by 
the city of Florence. The position of Galileo in the history of 
the Sciences is too well known to need more than passing notice, 
but the work of men like Redi, Viviani, Marsili, Dati, and Borelli 
is often overlooked or forgotten. Let us glance at the labours of 
the last-mentioned of these men — the Neapolitan Borelli. “A 
mathematician, a physician, an astronomer, he occupied himself 
with all subjeds, and thus supplied himself with ample materials 
for future discoveries. He studied the reciprocal actions of 
floating bodies ( galleggianti ), and discovered its theory ; he was 
the first to observe the variations of the barometer with the 
changes in the atmosphere ; he considered the question of the 
freezing of water ; he planned the experiments which were 
decisive against the idea of the positive lightness ( leggerezza 
positiva) ; he measured the greatest expansion of air freed from 
surrounding pressure ; he determined the weight of air compared 
with water ; he suggested the famous experiment with the silver 
ball, to test the compressibility of water; and another experi- 
ment on the propagation of sound {in vacuo) ; he studied the 
contraction of various liquids in cooling ; and in the researches 
on the velocity of propagation of light he was the first to con- 
struct the heliostat ( eliostata ) ;” . . . he also made various as- 
tronomical discoveries ; he was the first to observe the vena 
contracta , and he devised new experiments to illustrate Galileo’s 
idea of the fall of bodies in a vacuum. 
On the occasion of the next Conference Mr. Dewar described 
his Charcoal Vacuum , which he produces by placing charcoal in 
