58 



SCIENTIFIC NEVV^S. 



[Jan. 20, 18 



box. With that form, the manner in which the different 

 colours are got is easily followed. Confining the atten- 

 tion, by looking through the two eye-pieces, to the hght 

 passing through the centre of the ring, three overlapping 

 circles of light can be easily distinguished on the bottom 

 of the box — one red, another green, and the third violet. 

 Where the red and green overlap, a brilliant yellow is pro- 

 duced. Where the green and the violet overlap is a brilliant 

 blue. Where the red and the violet overlap, purple is 

 produced. And in the centre, where all the three circles of 

 red, green, and violet overlap, pure white is produced. 



For those who in their experiments do not require to 

 have such rigidly fine results, Mr. Aitken has designed a 

 much simpler instrument, represented in Figs. 3 and 4, 

 of which Mr. Aitken has kindly sent us the drawing. 

 This illustrates the production of an infinite variety of 

 colours from the three primary colours — red, green, and 

 violet ; but it has the disadvantage that its working is 

 not under control. As before, B is the eye-piece fixed to 

 the end of a brass tube about twenty inches in length ; 

 to the other end of the tube is fixed a circular piece of 

 wood (A), on which is mounted the three coloured glasses 

 (R G V). Fig. 3 represents the vertical longitudinal 

 section of the instrument, and Fig. 4 the end of it. C is 

 a brass plate, with an opening in the centre for holding 

 the glasses in their places. S is a circular blackened 

 disc, with an opening cut excentrically in it, which per- 

 forms the functions of the shutters in the other instru- 

 ment. K is a piece of ground glass, and U is a brass 

 ring for holding the glass in its place ; these are both 

 removed in the end view of the instrument. The opening 

 in S is carefully adjusted in size and position ; when the 

 disc rests in the position shown, then all three glasses 

 are exposed, and a disc of light, the resultant of the three 

 colours, is seen through B. Now suppose this opening 

 is turned to where it is shown in dotted lines, then only 

 violet light will get through it, and only a disc of violet 

 light will be seen. In using this instrument, it is held 

 up to the light and turned round its axis ; when this is 

 done, the revolving shutter (S) rolls round in its cavity, 

 and as it rolls, it varies the amount and colour of the 

 light received by B. In one position it allows light of 

 only one colour to enter ; in another it allows light of all 

 the colours to pass, and that in ever- varying proportions. 

 When the opening in the screen is at its extreme of 

 excentricity, it may allow light of only one kind to enter, 

 or it may allow light of only two kinds to be combined 

 in endless proportions ; and when it rolls from its 

 position of extreme excentricity to that of concentricitj', 

 the three colours are combined in unlimited variety. 

 Such an arrangement of three pieces of glass with the 

 three primary colours most ingeniously produces all the 

 possible shades and tints of colours that are known ; 

 and the beauty of it lies in the simplicity of its construc- 

 tion. It possesses all the charm of an ingenious toy, 

 while it produces scientific results only attainable by 

 complicated and expensive instruments. 



Colour experiments made with these chromomictors 

 explain why there is so little appearance of coloured 

 light in our cathedrals, even when there is much coloured 

 light entering through the stained glass windows ; and 

 they show that, though the windows be glazed with the 

 most brilliantly-coloured glass, yet the light in the interior 

 might be quite white. Such apparatus as these will 

 be found eminently useful for teaching physical optics, 

 for experiments on colour perception, and for measuring 

 the qualities of lights from diiierent sources. 



ACTION OF OILS ON METALS. 



ACCORDING to the American Journal of Railway Ap- 

 pliances, a series of experiments, which lasted over 

 twelve months, was carried out to ascertain the efiects- 

 of oils in contact with various metals. 



The metals to be tested were first thoroughly cleaned 

 with ether, and dried. The weights were then taken,, 

 and the metals placed in closed tubes filleaJ Avith. 

 the oils, and kept for twelve months at a mean tempera- 

 ture of 27° C. during the summer and 10° to 13" C. during 

 the winter. 



The following results were obtained : — 



Iron. — Least attacked by seal oil, and most affected by 

 tallow oil. 



Bronsc. — Not attacked by colza oil. Very little affected) 

 by olive oil ; but very considerable action produced by 

 cotton-seed oil. 



Lead. — Least acted upon by olive oil ; greatest action 

 noticed with whale oil. Lard and spermaceti oils have- 

 almost the same effect as whale oil. 



Zinc. — Seemed but little attacked by mineral lubrica- 

 ting oils. The least action was with lard oil, and the- 

 greatest with spermaceti oil. 



Copper. — Not attacked by mineral lubricating oils.. 

 Least affected by spermaceti oil, and most attacked by 

 tallow oil. 



The experiments show that mineral oils had the least, 

 effect upon the metals tested, and that the greatest actioR' 

 was produced by tallow oil. 



The following table gives a resume of the experi- 

 ments : — 



Proposed Scottish Academy of Science. — Prof. Dunn,, 

 in his introductory address, read before the Royal Physical 

 Society, urged that the principal scientific societies of Edin- 

 burgh should unite as a Scottish Academy of Science, each, 

 council to continue to manage the affairs of its own society 

 and its own funds, but the united councils to have powers- 

 to elect distinguished men as Academicians. 



Fixing Indian Ink Drawings. — The lines in drawings 

 made with Indian ink frequently "run " during the process oi 

 colouring ; this may be prevented by mixing the ink with a two» 

 per cent, solution of red chromate of potash, instead of ordi- 

 nary water. The potash salt, under the influence of light,, 

 forms an insoluble compound with the size with which the; 

 ink is prepared. 



Bleaching by Electricity. — An electrical process o£ 

 bleaching, of Russian origin, requires the mixture of 10 parts-, 

 sodium chloride, i part carbonate of soda or potash, i part 

 chlorate of soda or potash, i part glycerine, 87 parts water„ 

 whilst for silk bleaching simply solutions of sodium sulphate; 

 are required. By the electrical current oxygen is produced^ 

 at the positive pole, while, by reacting on the chloride, and by 

 a more complicated reaction, in which, according to th& 

 inventor, the carbonic acid also enters, ozone, oxygen, and 

 peroxide of hydrogen are stated to be produced. 



