mences and
judge of its absolutely reliable behavior as an instrument for public
demonstration. I may say that I have never, under any condition, found
this type of machine to fail in its performance.

[Illustration: Fig. 13.]

[Illustration: Fig. 14.]

I now propose to show you the beautiful appearances of the discharge,
and then, in order that you may judge of the relative capabilities of
each of these three machines, we will work them all at the same time.

The large frictional machine which is in use for this comparison is so
well known by you that a better standard could not be desired.

In conclusion, I may be permitted to say that it is fortunate I had
not read the opinions of Sir William Thomson and Professor Holtz, as
quoted in the earlier part of my lecture, previous to my own practical
experiments. For had I read such opinions from such authorities, I
should probably have accepted them without putting them to practical
test. As the matter stands, I have done those things which they said I
ought not to have done, and I have left undone those which they said I
ought to have done, and by so doing I think you must freely admit that
I have produced an electric generating machine of great power, and
have placed in the hands of the physicist, for the purposes of public
demonstration or original research, an instrument more reliable than
anything hitherto produced.

* * * * *

VIOLET COPYING INK.--Dissolve 40 parts of extract of logwood, 5 of
oxalic acid and 30 parts of sulphate of aluminium, without heat, in
800 parts of distilled water and 10 parts of glycerine; let stand
twenty-four hours, then add a solution of 5 parts of bichromate of
potassium in 100 parts of distilled water, and again set aside for
twenty-four hours. Now raise the mixture once to boiling in a bright
copper boiler, mix with it, while hot, 50 parts of wood vinegar, and
when cold put into bottles. After a fortnight decant it from the
sediment. In thin layers this ink is reddish violet; it writes dark
violet and furnishes bluish violet copies.

* * * * *

SIBLEY COLLEGE LECTURES.--1887-88.

BY THE CORNELL UNIVERSITY NON-RESIDENT LECTURERS IN MECHANICAL
ENGINEERING.

THE EVOLUTION OF THE MODERN MILL.[1]

[Footnote 1: The lecture was illustrated by about fifty views on
the screen, which cannot be reproduced here, showing photographs
of mills and mechanical