balance, while b is an empty glass bulb (floater).

These instruments are admirably adapted for determining the gravity of
alcohol, petroleum, benzine, and every kind of oil, also for testing
beer, milk, vinegar, grape juice, lye, glycerine, urine, etc.

As the process is an exceedingly simple one and free from the
drawbacks of the aræometer, we are justified in concluding that the
aræo-picnometer will soon be in general use.

H. HENSOLDT, Ph.D.

Petrographical Laboratory, School of Mines, Columbia College.

* * * * *

[Continued from SUPPLEMENT, No. 793, page 12669.]




GASEOUS ILLUMINANTS.[1]

[Footnote: Lectures recently delivered before the Society of Arts,
London. From the _Journal_ of the Society.]

BY PROF. VIVIAN B LEWES.


IV.