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1857.] must have been touching though they did not form a continuous film; and on the other hand, the difference between the effect here and with unattached gold-leaf, shows that the degree of' continuity as a film must be very small. When these heated films were greened by agate pressure, or the drawing pressure of a card, the green parts remained granulated, apparently in the same degree as when purple. The green was not subjective or an effect of interference, but a positive colour belonging to the gold in that condition. Every touch of the agate was beautifully distinct as a written mark. The parts thus greened and the purple parts appeared to transmit about the same amount of light. Though the film appeared granulated, no impression was made upon the mind that the individual particles of which the film consisted were in any degree rendered sensible to the eye.

The unheated gold films when pressed by agate often indicated an improved reflective power, and the light transmitted was also modified; generally it was less, and occasionally tended towards a green tint; but the effect of pressure was by no means so evident as in particles which had been heated.

Films of some other metals were reduced by phosphorus in like manner, the results in all these cases being of course much affected by the strength of the solution and the time of action; they are briefly as follows:—Palladium: a weak solution of the chloride gave fine films, apparently very continuous and stiff; the reflexion was strong and metallic, of a dark grey colour; the transmission presented every shade of Indian ink. Platinum chloride gave traces of a film excessively thin, and very slow in formation. Rhodium chloride in three or four hours gave a beautiful film of metal in concentric rings, varying in reflecting and transmitting power over light and also in colour; those which reflected well, transmitted little light; and those which transmitted, reflected little light; one might have thought there was no metal in some of the rings between other rings that reflected brilliantly, but the metal was there of transmitting thickness; the transmitted colour of rhodium varied from brown to blue. Silver: a solution of the nitrate gave films showing the concentric rings; the light transmitted by the thinner parts was of a warm brown, or sepia tint; the film becomes very loose and mossy in the thicker parts and is