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rOPULAR SCIENCE REVIEW. 
the cotton-wool which holds hack the numberless organic germs and dust- 
particles floating in the atmosphere. The air thus cleansed passes into 
U-shaped vessel, where it is dried by the sulphuric acid. It then descends 
through the narrow tube to the bottom of the little flask, and escapes 
there through a small orifice into the liquid. Through this it bubbles, 
loading itself to some extent with nitrite of amyl vapour, and then the air 
and vapour enter the experimental tube together. We will now permit the 
electric beam to play upon this invisible vapour. The lens of the lamp is 
so situated as to render the beam convergent, the focus being formed 
about the middle of the tube. You will notice that the space remains dark 
for a moment after the turning on of the beam ; but the chemical action 
will be so rapid that attention is requisite to mark this interval of darkness. 
I ignite the lamp ; the tube for a moment seems empty ; but a luminous 
white cloud immediately fills the beam. It has in fact shaken asunder the 
molecules of the nitrite of amyl, and brought down upon itself a shower of 
particles, which cause it to flash forth in your presence like a solid luminous 
spear. This experiment, moreover, illustrates the fact that however intense 
a beam of light may be, it remains invisible unless it has something to shine 
upon. Space, though traversed by the rays from all suns and all stars, is 
itself unseen. Not even the ether, which fills space, and whose motions 
are the light of the universe, is itself visible.” 
We take the foregoing, as one of the most striking of the novelties in this 
admirable work, and also one of the most interesting of the recent facts re- 
corded by the author. But the whole work is full of such, and we cannot 
do better than recommend those of our readers who are already unfamiliar 
with it, to procure it for themselves at once. It is not only the best work 
on the subject in the English language, but it is in itself especially valuable 
as an eloquent and comprehensive treatise. 
BUILDING.* 
T HE author tells us of this work, that he has endeavoured to introduce 
the student of architecture to a general outline of scientific subjects 
connected with his profession, an acquaintance with which at present in- 
volves the reading of a large amount of works by various authorities. By 
so doing, he hopes to command the attention of the great mass of architects, 
f<»r the mathematical knowledge required to understand what he has got to 
disclose, does not extend beyond elementary geometry and algebra. The 
book is divided into seven chapters, dealing with the following subjects : 
mechanical principles, retaining walls, arches and cupolas; building stones, 
timber, iron, and lastly water contained in vessels and pipes. So far as we 
have examined, the book seems clear and intelligibly arranged ; but we 
must differ from the author, when he says, as he does say, that it is the 
only work of its kind. Unfortunately, too many books of all kinds are pub- 
• “The Science of Building. An Elementary Treatise on the Principles 
of Construction, especially adapted to the requirements of Architectural 
Students.” By E. Wyndham Tam, M.A., Lond. London : Lockwood, 1870. 
