TRANSACTION'S OF THE SECTIONS. 65 



On an improved Form of Air Pump for Philosophical Experiments. 



By W. Ladd. 



On the Chromoscope. By John Smith, M.A., Perth Academy. 



The author sent a specimen of the cut-out card, by the rotation of which, in 

 strong light, as sunshine, he could produce various colours. There were also dia- 

 grams exhibited painted so as to represent the several colours and tints which the 

 author had succeeded in causing to appear. The chromoscope, he said, was not the 

 result of a happy accident, but was constructed to verify certain opinions which he 

 had long entertained as to the cause of colour; that it not only produced colour, but 

 explained the principle on which it was produced, and proved the necessity of intro- 

 ducing a negative term into the theory of colour — the purpose for which it was con- 

 structed. On the theory he said he would not enter, as he had explained it at the 

 Meeting at Aberdeen, when he also made some experiments before Section A. 



The author's object at present was to direct attention particularly to what he 

 considered a most remarkable phenomenon connected with these experiments, which 

 manifested itself in the change of colour which took place when the motion of the 

 figure was reversed. The simplest illustration given, was a semidisc divided into a 

 number of concentric rings of equal breadth, each alternate ring being painted black 

 or cut out of the card, and tbe card fixed on the axle of the machine at a point, 

 exactly equal to half the breadth of one of the rings, from the centre of the disc. 

 When the card is made to rotate, each ring is thus divided into two equal sections, 

 and the section of a black ring is superposed, as it were, on a white, or a white on 

 a black when in motion ; or in each revolution of the machine there is produced a 

 sensation of light and no light on the same spot of the retina. In this experiment 

 each contiguous ring has a different colour, one purple, the other a greenish yellow, 

 and each alternate ring has the same colour. 



Reverse the motion, the rings which were purple will now be yellow, and vice 

 versa, those which were yellow will be purple. 



There was another diagram giving an analysis of this ; showing how all the rings 

 could be made of one colour, exhibiting discs wholly of purple rings, or wholly of 

 yellow rings. 



He said that in these experiments, when the revolutions of the machine were more 

 than thirty-two in a second of time, all colour was lost to the eye ; among other 

 reasons, demonstrating to the mind of the author, that the pulsations of light are 

 not so frequent as science represents them to be. He considered every revolution of 

 the machine equivalent to an effective pulsation of light ; and that the usual experiment 

 of placing the prismatic colours on a wheel, and making them revolve, only proves the 

 inability of the eye to estimate such rapid vibrations, and not the composition of 

 white light, for the colour produced is a gre}', not white, and so is the colour of his 

 cards when in such rapid motion. 



To represent refracting substances, such as prisms or other transparent crystals 

 of any form, the author said it was necessary to make the cards revolve perpendi- 

 cularly, in order to produce the form of a solid. Several of these were shown to 

 the Section. A section of a ring produced the figure of a vase of a pink colour, with 

 a greenish centre. A semiring produced a vase of a different form and of various 

 colours, the brim being of a deep purple. A scroll composed of two semirings pro- 

 duced a strange compound figure, the predominant colour being a deep dark green. 



Along these figures, in given conditions, there is a dark or a bright line, which he 

 said was the axis of motion, and might be considered as the line of no motion or of 

 no reflexion, or of intermittent reflexion, according to the construction of the figure. 

 The card can be cut so as to represent both phases — the black and the coloured — in 

 the same figure. 



The author in his paper said, " Are not these phenomena very like those of 

 polarized light?" only more astonishing, and more within the range of human 

 research. After looking at these experiments he always felt disposed to put the 

 question, " What now is polarized light ?" 



He also added that the horizontal and perpendicular experiments were constructed 

 on the same principle, and that the colours are the result of the same law. 



1860. 5 



