Since spiritualists claim that the presence of invisible spirits may be detected by photography, it seems reasonable to inquire how far this is compatible with established physical facts. If a plate is wrapped in paper and submitted to “spirit influences”—whatever these may be—never being exposed in a camera at all, and on development shows faces or writing, I personally can only find one explanation—trickery. But if a plate is duly exposed with camera and lens, and unseen faces appear on development, the matter is not quite so simple. For it is well recognised that the camera may record what is invisible to the eye; invisible stars are detected by the photographic plate, and anyone who has examined a nebula or comet through a telescope, after seeing a photograph of the same object, realises this fact to his disappointment. Similarly a can of hot water may be photographed, by a long exposure, in a perfectly dark room; and another well-known instance of a similar phenomenon is Sir Robert Ball’s story of photographing some writing on the side of the “Great Eastern,” years after it had been painted out and rendered invisible.

Light, as is well known, is now regarded as consisting of waves in the ether. Ether waves are known to exist over a very large range of wave-lengths; some are comparatively long waves, some are short. The properties of these waves depend upon their wave-length; those visible to our eyes, which we call “light rays,” form only a small section of the complete scale; comparing them with sound waves they correspond to approximately one octave of the whole musical scale. Ether waves of greater or lesser wave-length than light, i.e., of lower or higher octaves, have very different properties. Radiant heat and ultra-violet rays are the ether waves nearest in wave-length and properties to light; X-rays and the waves responsible for wireless telegraphy appear to be similar waves further removed along the scale of wave-length.

Now in order to photograph an invisible object we require rays that (a) affect a photographic plate; (b) are capable of refraction by a lens; and (c) are invisible to the eye. The properties of the principal known rays concerned may be summarised as follows:

Effect on Plates Refracted by Lenses Visibility
Infra-red (heat) rays v. slight Yes No
Light rays affected Yes Yes
Ultra-violet rays strongly affected Yes No
X-rays affected No No

It appears, then, that ultra-violet rays are suitable for our purpose; infra-red rays, if present in an amount sufficient to affect a photographic plate, would make themselves very evident as heat, and may therefore be ruled out.

Ordinary daylight contains ultra-violet rays, as also does the light of the arc lamp and magnesium flash; lamplight, gas-light, and the ordinary electric light, are comparatively deficient in them. But are we to assume that the spirit form is dependent on finding suitable rays in the surrounding ether, or can it produce its own? Perhaps some spiritualist will tell me. This is a point of some practical importance in examining a reputed spirit photograph; for if the spirit is self-luminous its features will be evenly illuminated and without shadows, nor will it cast a shadow on the sitter or background, but rather the reverse. If, on the other hand, the spirit is dependent on the presence of ultra-violet rays from other sources, which it can reflect, then the spirit in the photograph will appear to be illuminated from the same point as the sitter,[9] and by absorption or reflection of the ultra-violet actinic rays which would otherwise have passed on, will cast a shadow on the background. Being a shadow cast by the removal of the ultra-violet rays only, it will of course appear as such in the photograph, but be invisible to the eye.

So if a spirit photograph is to be classed as possibly genuine, the spirit may either appear self-luminous and cast no shadow, or may appear to be illuminated from the same point as the sitter, and cast a shadow on the background, if the latter be of a suitable nature to show it. But on examining a collection of spirit photographs taken by various professional mediums, we find that as often as not the spirit and sitter are lighted from opposite sides; or that a spirit face with a well-marked shadow on one cheek throws no shadow on the background. If our reasoning be correct, we can at once write such productions down as frauds. The photographs I produced at my Cambridge séances show both these faults; two of them have the spirits lighted from the opposite side to the sitter, and one has the spirit lighted from the correct side but throwing no shadow, whereas the sitters throw clear shadows on the wall behind. In the other photograph I managed to get both the lighting and the shadow of the spirit correct; but in order to get the shadow I had to photograph the background with the “spirit”; hence when the sitters were photographed on the same plate there was a double background, which necessitated a rapid destruction of the plate!

Of course the average medium does not consider these points at all; his sitters are usually satisfied with anything they can get, so why should he worry? But an intelligent observer examining a number of spirit photographs with regard to these points will quickly satisfy himself that the majority of them can only be frauds.[10]

There are a number of other points by which a spirit photograph may betray its method of production without reference to the conditions under which it was taken. Many spirit extras are simply copies of existing photographs, which are usually camouflaged in some way. Draperies may be substituted for the hair, or the features slightly retouched. A common method is to reverse the original photograph, right for left; a number of Hope’s productions were recently published in a monthly magazine, and alongside them life portraits of the “spirits,” the letterpress emphasising that, though undoubtedly the same face, they were different photographs. On examination with a mirror, however, the photographs were seen to be identical, and careful measurement of the faces showed the proportions to be exact. In the photographs more recently published by Mr. Bush, who laid a trap for Hope into which the latter appears to have fallen, the spirit was not reversed, nor was even the rather peculiar attitude of the head in the original photograph altered. A little spirit drapery was added round the face, and the whole thrown slightly out of focus; it is really a most clumsy piece of work, and should deceive no one.

In some spirit photographs produced by double exposure there is a double background, as occurred in my own photograph referred to above. There may be either two different backgrounds, or a double outline of the same background; in either case the “spirit’s background” is usually fainter than the “sitter’s background,” and shows through the darker parts of the sitter. Sometimes attempts are made to retouch these appearances on the negative, and many spirit photographs show clumsy brush or pencil work, which must immediately stamp them as frauds.