dom.

To aid in a feeble way for the protection of posterity I have
formulated ten rules on the preservation of vision:

(1) Do not allow light to fall upon the face of a sleeping infant.

(2) Do not allow babies to gaze at a bright light.

(3) Do not send children to school before the age of ten.

(4) Do not allow children to keep their eyes too long on a near
object, at any one time.

(5) Do not allow them to study much by artificial light.

(6) Do not allow them to use books with small type.

(7) Do not allow them to read in a railway carriage.

(8) Do not allow boys to smoke tobacco, especially cigarettes.

(9) Do not necessarily ascribe headaches to indigestion. The eyes may
be the exciting cause.

(10) Do not allow the itinerant spectacle vender to prescribe glasses.

* * * * *

THE WATER MOLECULE.[1]

[Footnote 1: Translated from the _Pharmaceutische Centralhalle_, by
A.G. Vogeler.--_Western Druggist_.]

By A. GANSWINDT.

"Water consists of one atom of oxygen and two atoms of hydrogen." This
proposition will not be disputed in the least by the author; still, it
may be profitable to indulge in a few stereo-chemic speculations as to
the nature of the water molecule and to draw the inevitable
conclusions.

From the time of the discovery, some 110 years ago, that water is a
compound body, made up of oxygen and hydrogen, the notion prevailed up
to within a quarter of a century that it was composed of even
equivalents of the elements named, and all but the youngest students
of chemistry well remember how its formula was written HO, the atomic
weight of oxygen being expressed by 8, making the molecular weight of
water (H=1 + O=8) 9. But the vapor density of water, referred to
air, is 0.635, and this number multiplied by the constant 28.87, gives
18 as the molecular weight of water, or exactly twice that accepted by
chemists. This discrepancy led to closer observations, and it was
eventually found that in decomposing water, by whatever method
(excepting only electrolysis), not more than the eighteenth part in
hydrogen of the water decomposed was ever obtained, or, in other
words, only just one-half the weight deducible from the formula HO =
9. The conclusion was irresistible that in a water molecule two atoms
of hydrogen must be assumed, and, as a natural sequence, followed the
doubling of the molecular weight of water to 18, represented by the
modern formula H