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Page 38
Figures are characters without physiognomy, if we may so express
ourselves, while the spots on the dominoes take particular
arrangements according to the number represented, and differentiate
themselves more clearly from each other than figures do. They are at
the same time more easily read than figures or regularly spaced dots.
Now, it is very important to fix the attention upon the numbers, since
they are arranged at distances expressed in dioptries and indicated by
the number of the spots. On looking through the aperture, we see in
the first place one of the dominoes more distinctly than the rest.
Then, on endeavoring to see those that are nearer or farther off, we
succeed in accommodating the eye and in seeing the numbers that
express the extreme terms of the accommodation, and consequently the
amplitude.
[Illustration: FIG. 3.--DETAILS OF EYE PIECE.]
Let us now take some examples: If we wish to express in dioptries the
myopia of a person, we put the apparatus in his hand, and ask him to
place his eye very near the aperture and note the number of spots on
the most distant domino that he sees distinctly. This is the number
sought. If the observation be made through the upper lens, it will be
necessary to subtract five from the number obtained; if, on the
contrary, the other lens is used, it will be necessary to add six.
If it is a question of a presbyope, let him look with his spectacles,
and note the nearest domino seen distinctly. This will be the number
of dioptries expressing the nearest point at which he can read. This
number permits us to know whether it is necessary to add or subtract
dioptries in order to allow him to read nearer by or farther off. If,
for example, he sees the deuce and the ace distinctly, say 3 dioptries
or 0.33 meter, and we want to allow him to read at 0.25 meter,
corresponding to four dioptries, it will be necessary to increase the
power of his spectacles by one dioptrie.
Upon the whole, Dr. Bull's optometer permits of measuring the
amplitude of accommodation, and, consequently, of obtaining the
approximate age of people, of knowing the extreme distances of the
accommodation, and of quickly finding the number of the glass
necessary for each one. It reveals the defects in the accommodation,
and serves for the quick determination of refraction. So, in saying
that this little instrument is very ingenious and very practical, Dr.
Javal has used no exaggeration.--_La Nature._
* * * * *
THE SANITATION OF TOWNS.[1]
[Footnote 1: Abstract from the presidential address delivered
before the Association of Municipal and Sanitary Engineers and
Surveyors, at the annual meeting in Leicester, July 18, 1887.]
By Mr. J. GORDON, C.E.
The average mortality for England and Wales was 22.4 in 1838, and in
1886 19.3, which shows a saving on last year's population of England
and Wales of 86,400 lives annually, and a saving in suffering from an
estimated number of about 1,728,000 cases of sickness. To accomplish
all this, vast sums of money have been expended, probably not always
wisely, inasmuch as there have been mistakes made in this direction,
as in all new developments of science when applied in practice, and
evils have arisen which, if foreseen at all at the outset, were
underrated.
The great object of the public health act, 1848, was to enable local
authorities by its adoption to properly sewer, drain, and cleanse
their towns, and to provide efficient supplies of water, free from
contamination and impurities dangerous to health. The raising of money
by loans repayable in a series of years, which the act empowered,
enabled all these objects to be accomplished, and, while the first
duty of local authorities was undoubtedly the provision of a good
supply of water and proper sewerage for the removal of liquid filth
from the immediate vicinity of inhabited dwellings, the carrying out
of proper works for the latter object has been of much slower growth
than the former. Private companies led the way, in fact, in providing
supplies of water, inasmuch as there was a prospect of the works
becoming remunerative to shareholders investing their money in them;
and in nearly every instance where local authorities have eventually
found it to be in the interests of the inhabitants of their districts
to purchase the work, they have had to pay high prices for the
undertaking. This has generally led to a great deal of dissatisfaction
with companies holding such works, but it must not be forgotten that
the companies would, in most instances, never have had any existence
if the local authorities had taken the initiative, and that but for
the companies this great boon of a pure supply of water would most
probably have been long delayed to many large as well as small
communities.
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