ds of the latter.

So far as scientific operations were concerned, the views of the
commission were harmonious through the whole of their deliberations.
It was agreed from the beginning that the photographic method
offered the greatest promise of success. But how, with what sort
of instruments, and on what plan, must the photographs be taken?
Europeans had already begun to consider this question, and for the
most part had decided on using photographic telescopes having no
distinctive feature specially designed for the transit. In fact,
one might almost say that the usual observations with the eye
were to be made on the photograph instead of on the actual sun.
The American commissioners were of opinion that this would lead to
nothing but failure, and that some new system must be devised.

The result was a series of experiments and trials with Professor
Winlock's instrument at the Cambridge Observatory. The outcome of
the matter was the adoption of his plan, with three most important
additions, which I shall mention, because they may possibly yet be
adopted with success in other branches of exact astronomy if this
telescope is used, as it seems likely it may be.

The first feature was that the photographic telescope should be
mounted exactly in the meridian, and that its direction should be
tested by having the transit instrument mounted in front of it,
in the same line with it. In this way the axis of the telescope
was a horizontal north and south line.

The next feature was that, immediately in front of the photographic
plate, in fact as nearly in contact with it as possible without
touching it, a plumb line of which the thread was a very fine silver
wire should be suspended, the bob of which passed down below, and
was immersed in a vessel of water to prevent vibration. In this way
the direction of the north and south line on the plate admitted of
being calculated with the greatest exactness, and the plumb line being
photographed across the disk of the sun, the position angle could be
measured with the same precision that any other measure could be made.

The third feature was that the distance between the photographic
plate and the object glass of the telescope should be measured by
a long iron rod which was kept in position above the line of sight
of the telescope itself. This afforded the means of determining
to what angle a given measure on the plate would correspond.
The whole arrangement would enable t