96 M. NOBILI OX COLOURS, AND ON A NEW CHROMATIC SCALE 



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 per- 

 fect voice. I have shown my scale to several, and especially to those eru- 

 dite 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 

 M'hich 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 co- 

 lour of the thinnest plate is placed first, and the others follow in the order 

 of the progressively increasing thickness of the plates*. In this arrange- 

 ment 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 laj'er 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 colom-s. These 

 numbers are taken from Newton's table, the fractional parts only being omitted. 

 The numbers are those wliich apply to thin layers of water. The unit of mea- 

 sure is the milHonth part of an Enghsh inch. Our scale should then commence 

 with a layer measu'-ing 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, atleast the relative thickness of the attenuated layers 

 which eflectively cover our plates of steel. 



