Intelligence and Miscellaneous Articles. 559 



in many respects suitable, are plainly beyond the reach of most ob- 

 servers ; and the only system which appears to possess the requisite 

 qualification is that of chemical solutions, before referred to. 



The " Metro chrome," which it is the author's object to describe, 

 is shown in side-section and by a face-view in two figures given in 

 the original paper. It consists essentially of three parts : (1) a lan- 

 tern for the production of a constant light ; (2) a contrivance for 

 imparting to that light the necessary colour, and so arranged that, 

 the proper tinge once produced, a record of it can be obtained so as 

 to enable it to be reproduced at any time ; (3) apparatus to throw that 

 coloured light into the field of the telescope as an artificial star 

 which can thus be viewed side by side with the image of the real one. 

 The source of light is a very fine platinum wire, rendered incan- 

 descent by a current of electricity transmitted through it from a 

 Smee's battery of two cells. The platinum wire is brought into the 

 focus of a lens, so that the rays of light from the lantern issue parallel, 

 and therefore come to a focus, after passing through the object-glass 

 of the telescope, at the same distance from it as those emitted by a 

 star. The chromographic part of the apparatus consists of a drum 

 rotating about an axis. The drum has in it six equidistant radial 

 openings — the alternate three of them transmitting the normal light 

 of the lantern, the other three constructed so as to admit flat-sided 

 stoppered bottles containing chemical solutions of different colours. 

 The outer edge of each of the last-mentioned apertures is graduated 

 into ten parts, and each of them can be wholly or partially closed by 

 means of a radial shutter ; the other three apertures can be simulta- 

 neously closed, wholly or partially, by a triune radial shutter : the 

 edge of one of them is divided into ten parts ; and as all are equally 

 affected by the movement of the shutter, the reading applies to the 

 three openings. The drum is made to rotate so as to bring succes- 

 sively the different apertures in front of the lantern ; and when the 

 rotation is sufficiently rapid, the impression of colour produced on 

 the retina of the eye will be that of a colour compounded of the co- 

 lours of the solutions in the three alternate apertures, diluted by the 

 white light transmitted through the other three alternate apertures. 

 By a proper selection of the solutions, and adjustment of the magni- 

 tude of the several apertures by means of the shutters, it will be pos- 

 sible to produce the exact colour of a particular star ; and then the 

 record of the solutions employed, and of the dimensions of the several 

 apertures, will enable the exact reproduction of such colour at any 

 future period for comparison with the then colour of the star in 

 question. The remaining part of the apparatus is a contrivance for 

 throwing the beam of coloured light into the telescope so as to pro- 

 duce, as already mentioned, the image of an artificial coloured star. 

 — Monthly Notices of the Royal Astronomical Society, May 10, 1867. 



