1 877.] 
Notices of Books. 
271 
to 15 metres of vertical height) in the reservoirs of the city. 
In London there are twenty-five pneumatic tubes representing a 
length of 18 miles. The tubes are 2^ inches diameter, and are 
worked by alternately compressing and exhausting air by means 
of three steam-engines, each of fifty horse-power. In New 
York passengers are conveyed by the same means. 
A curious misprint, twice repeated, occurs on p. 81 ; Hero’s 
Fountain is printed Nero's Fountain : the same error occurs 
twice on the following page. A chapter on ballooning concludes 
the first book. 
In the second book, on Acoustics, we have a useful sedlion on 
“ Acoustics applied to Architecture then a description of 
various musical instruments, ancient and modern, including a 
most capital account of the construction of the violin, “the most 
perfeCt of musical instruments. The back and ribs of the violin 
are made of a hard close-grained wood, usually beech ; the 
upper plate or belly is made of a light wood, such as deal or 
cedar. The old violin-makers preferred Swiss pine for the belly 
and maple for the back. An effective woodcut (fig. 96) shows 
the various parts of the instrument. Although, as is well known, 
violins improve considerably by age, our author very justly 
remarks — “ But it must not be forgotten that the beauty of the 
tone of an instrument of this kind depends, in great measure, on 
the talent of the artist in whose hands it may be. Nearly his 
whole skill, from this point of view, lies in regulating the 
pressure by which his right arm, or more properly speaking his 
right hand, direCts the bow, and the clearness and force with 
which the fingers of the left hand press the string.” The com- 
plex mechanism of the harp is well shown in fig. 109. An 
interesting account of the great organ at Primrose Hill, built by 
Bryceson Bros., is given in Chapter 5. This fine instrument 
embraces seven distindl organs, and the bellows and “ vacuum 
pressure ” are worked by an eleven horse-power steam-engine. 
There are seventeen compressed-air reservoirs, and two vacuum 
reservoirs. The echo organ — 100 feet distant from the keyboard 
— is worked both by electricity and by vacuum pressure, that is, 
the pressure produced by air striving to enter a vacuum. The 
32-feet pipes in the great organ in Notre Dame each require 
70 litres of air a second to sound them, while the whole mass of 
compressed air in the organ amounts to 25,000 litres. 
The third book treats of the applications of the laws of Light, 
and first of mirrors and refleCtors, and of instruments in which 
mirrors are used, such as the sextant and goniometer, the 
heliostat and siderostat. A good account of lighthouse appli- 
ances follows : figures are given of the azimuthal condensing 
prisms used in the Sound of Skye, and of the peculiar form of 
lens used in the Tochindall lighthouse. 
The chapter on the Microscope contains some beautiful coloured 
drawings, among which we may specially call attention to the 
