enton, the secretary of the Photographic Society, takes his
stereoscopic pictures, when the objects are 50 feet and upwards from the
camera, at 1 in 25. This is, as MR. SHADBOLT states, Professor Wheatstone's
rule for distances. {17}

MR. WILKINSON, on the other hand, asserts that 3 feet in 300 yards is
sufficient separation for the cameras: this is only 1 in 300,--a vast
difference truly.

"For views across the Thames," says the editor of the _Photographic
Journal_, "the cameras should be placed 12 feet apart, and with this
separation the effect is declared to be astonishing."

MR. WILKINSON, however, asserts that from 4 to 6 feet in a mile will do
_well enough_!

Farther, Mr. Latimer Clark (the inventor of an ingenious stereoscopic
camera) states that with regard to the distance between the two positions
of the cameras, he knows no good reason why the natural distance of the
eyes, viz. 2-1/2 inches, should be much exceeded. "A little extra relief is
obtained," he adds, "without visible distortion, by increasing the
separation to about 4 or 5 inches; but if this distance be greatly
exceeded, especially for near objects (I give the gentleman's own words),
they become apparently diminished in size, and have the appearance of
models and dolls rather than natural objects."

The reason for making the separation between the cameras greater than that
between the two eyes, is exceedingly simple. The stereograph is to be
looked at much _nearer_ than the object itself, and consequently is to be
seen under a much larger angle than it is viewed by the two eyes in nature.
Hence the two pictures should be taken at the angle under which they are to
be observed in the stereoscope. Suppose the object to be 50 feet distant,
then of course it is seen by the two eyes under an angle of 2-1/2 inches in
50 feet, or 1 in 240. But it is intended that the stereograph should be
seen by the two eyes when but a few inches removed from them, or generally
under an angle of 2-1/2 in 12 inches, or nearly 1 in 5. Hence it is
self-evident that the stereoscopic angle should be considerably larger than
that formed by the optic axes of the two eyes when directed to the object
itself.

But there is great diversity of opinion as to the extent of the angles
requisite for producing the precise stereoscopic or distantial effect of
nature. For myself I prefer Professor Wheatstone's rule, 1 in 25 for
objects beyond 50 feet distant. For portraits I find the