248 SEC. 7. LIGHT. 



To demonstrate the absorption phenomena of soluble colouring matters, 

 plates of isinglass, which had been dyed with the colouring matter, are re- 

 commended, instead of the solutions. To protect these plates against dust, 

 &c., they may be placed between two glass plates. By placing feebly 

 coloured plates in a fan- shaped way upon one another, the increase of absorption 

 by increasing thickness may easily be illustrated. 



972. Mixoscope (colour-mixer), executed according to the 

 directions of the exhibitor by M. Ph. Edelmann, Munich. 



Prof. W. von Bezold, Royal Polytechnic School, 

 Munich. 



This apparatus gives the true colour resulting from the combination of two 

 colours by actual trial with the brush, and thus a correct colour table can, by 

 its means, be made with greater facility than with the revolving disc. The 

 achromatised calcspar prism is so to be adjusted that on looking through the 

 apparatus only six squares should be visible. It is easy to find this position 

 through moving the telescope and turning the prism. On bringing the two 

 colours to be mixed under two of the square openings, these colours will be 

 right and left of the mixed colour, which fills the middle part of the three 

 contiguous squares. If, now, the other two apertures contain the true optical 

 compound colour, the two central squares will appear in the same tint. 



Compare the description annexed to the apparatus. 



973. Clockwork for colour discs, for lecture purposes, 

 according to Kiihne's and Becker's principles. 



Rud. Jung, Heidelberg. 



The clockwork, provided with a strong spring, is capable of rotating 

 coloured discs of 28 centim. diameter with such velocity that a disc covered 

 with the tints of the spectrum will appear white. By a simple contrivance the 

 one or the other of the spectrum colours can be excluded, and thus its com- 

 plementary and contrast colour produced. By inserting a second axle, the 

 movements of the clockwork can be retarded. 



1065a. Colorimeter. M. Laurent^ Paris. 



3659. Three Diaphragms and lamp stand for magic lantern. 



Laurent. 



3659a. Diaphragms (4), various. Laurent, Paris. 



974. Apparatus for demonstrating the Glory on bedewed 

 Meadows, consisting of glass globes filled with water. 



Prof. Dr. Lommel, Erlangen. 



975. Apparatus for demonstrating the Glory on bedewed 

 Meadows, with solidified drops of Canada balsam. 



Prof. Dr. Lommel, Erlangen. 



These glass globules serve to demonstrate why dew drops shone upon by the 

 sun appear so brilliant just round the shade of the head of the observer. The 

 explanation is that each dew drop is a lens concentrating the rays upon the 

 ground below the drop, which latter sends them back diffused. 



If the glass globules are placed upon a sheet of white paper, and the shadow 

 of the observer's head is permitted to fall into the circle, the globules will 



