Geometrical demonstration of the formula.
demostration

Lesson 3. Integration of Differentials ...
Lessons 3.

[DESCRIPTIVE GEOMETRY.—GEOMETRICAL DRAWING.]

Lessons 1-3. Revision and Completion ...
. missing

not enough in themselves to define objects completely.
final . missing or invisible

Lessons 3-6. Composition of the Velocities of a Point.
period . after “3-6” invisible

three movements of translation with respect to three axes
tranlation

of invariable form, but also in motion.
motion,

Suspendors
spelling unchanged

Lessons 1-2. / Chemical sources of electricity.
period . after “1-2” missing or invisible