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POPULAR SCIENCE REVIEW. 
yet published. From his work — the latest, as it is unquestion- 
ably the fullest and most admirably illustrated volume on 
the subject — we perceive that his modification of the original 
aeroscope has been but very slight. It appears (A, fig. 1) to 
consist of three thin brass tubes, two of which slip over 
the third central one, and come into contact with the opposite 
sides of a projecting rim on its circumference. This rim 
is formed by the margin of a diaphragm which divides 
the central tube into two chambers. “It is of sufficient 
thickness to allow of a spindle passing up through it (fig. 1, B). 
The latter ends in a pointed extremity, which comes in contact 
with the upper end of the bearing, and provides for the free 
rotation of the system of tubes. Round the margin of the dia- 
phragm there is a set of perforations to allow of the passage 
of air through it, and in the centre of its anterior surface there 
is a square plate of brass, with a slightly projecting rim on its 
lower margin. The anterior of the two lateral tubes is pro- 
vided with an expanded orifice, and contains a small finely- 
pointed funnel in its interior ; the pointed extremity opening 
immediately in frqnt of the centre of the diaphragm plate. 
The posterior tube is quite simple, and has a good-sized fish- 
tail vane fitted into a slit in its extremity.” Such is the con- 
struction of the aeroscope, and when used, as it was most 
extensively by Dr. Cunningham in his late inquiries, it is placed 
at a height of about 4J ft. from the ground, and is allowed to 
revolve by means of a joint in such a manner that, owing to the 
vane, it is invariably exposed with its mouth to the wind. 
Hence if it is left, as it usually is, in one place for 24 hours, and the 
wind is blowing at even a rate of three or four miles an hour, the 
quantity of air that must traverse it is indeed most considerable. 
And now, how is the capture of the wind’s contents provided 
for? Very simply indeed. A microscopic covering-glass is 
carefully cleaned, and one of its surfaces smeared over with 
pure glycerine. A minute drop of the same is placed on the 
diaphragm-plate, and the dry surface of the cover-glass applied 
to it, leaving the smeared side exposed. (This did away with 
the necessity for springs.) Then the anterior tube being put 
on, it was ready for use. Now it is perfectly clear that with such 
an instrument it is easy to examine any amount of air, and its 
use has been often tried by Dr. Cunningham ; with what results 
we shall speak of presently. But in the first instance it will 
be as well to describe some of the consequences that have fol- 
lowed on attempts in the same direction by other workers, and 
to divide them into those who connect the contents of the atmo- 
sphere at certain seasons with certain infectious or contagious 
diseases, and those who take quite an opposite view of the 
matter. 
