was shown in operation. This consisted simply of a coil of thick
conductor suspended by a torsion wire, and opposed laterally to a fixed
coil of wire of high resistance. The current to be measured flowed
through both coils in parallel circuit, the one representing its
quantity expressible in amperes, and the other its potential expressible
in volts. Their joint attractive action expressed therefore volt-amperes
or watts, which were read off upon a scale of equal divisions.

The lecture was illustrated by experiments, and by numerous diagrams and
tables of results. Measuring instruments by Professors Ayrton and Perry,
by Mr. Edison and by Mr. Boys, were also exhibited.

* * * * *




ON THE PREPARATION OF GELATINE PLATES.

[Footnote: Being an abstract of the introductory lecture to a course on
photography at the Polytechnic Institute, November 11.]

By E. HOWARD FARMER, F.C.S.


Since the first announcement of these lectures, our Secretary has asked
me to give a free introductory lecture, so that all who are interested
in the subject may come and gather a better idea as to them than they
can possibly do by simply leading a prospectus. This evening, therefore,
I propose to give first a typical lecture of the course, and secondly,