the attempts hitherto made give little or no hope that the best executed copies can give more than an imperfect idea of the original colours.
The effect produced by these tints when disposed in the order set forth in the scale baffles description; it bears a resemblance however to that produced on the ear by a scale of semitones executed by a perfect voice. I have shown my scale to several, and especially to those erudite and learned persons who have favoured me with a passing visit at Reggio. In all it excited but one feeling of delight. So gradual indeed is the transition from one tint to another and such the harmony with which they are blended, that if the eye be accidentally turned away, it reverts in a moment as if moved by an irresistible desire to gaze still longer on the display. This statement is no exaggeration. It is but the mere fact, in respect to which a language much more glowing would be perfectly consistent with truth: so overpowering is the charm which, if I may use the expression, pervades the scale of our coloured plates.
Chromatic Scale.
This scale consists of forty-four tints, each of which is applied to a plate of steel. A Table subjoined to this Memoir exhibits the forty-four plates arranged one under the other in a column, and opposite to each number is the name of its peculiar tint. These tints are disposed in the same order as the layers or thin plates by which they are produced. The colour of the thinnest plate is placed first, and the others follow in the order of the progressively increasing thickness of the plates[1]. In this arrangement I cannot be mistaken, because the layers or thin plates which produce the several colours are all applied by the same electro-chemical process. The pile, the solution, the distances remain exactly the same. There is nothing variable but the duration of the action, which in respect to the layer No. 1. is very short, a little longer in respect to the second, and increases progressively from the lowest to the highest number. Other criterions also contribute to verify the accuracy with which its place is assigned to each tint.
These colours are produced by very thin layers or plates analogous to those which produce the colours in soap-bubbles and the rings observed
- ↑ The numerals placed within parentheses (in the Table) are designed to indicate the thickness of the plates which produce the different colours. These numbers are taken from Newton's table, the fractional parts only being omitted. The numbers are those which apply to thin layers of water. The unit of measure is the milionth part of an English inch. Our scale should then commence with a layer measuring four of these units in thickness and end with a layer measuring thirty, if we suppose our electro-chemical layers to possess the same refractive power as water. It is probably somewhat less. At all events it is useful to have these numbers immediately before our eyes, in order that we may know, if not the absolute, at least the relative thickness of the attenuated layers which eflectively cover our plates of steel.
