1867.] Physics. 551 



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 chroinographic part of the apparatus con- 

 sists of a drum rotating about an axis. The drum has in it six 

 equi-distant radial openings — the alternate three of them trans- 

 mitting 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 simultaneously closed, wholly or par- 

 tially, 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 aj^plies to the three openings. The drum 

 is made to rotate so as to bring successively 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 colours 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 magnitude of the several 

 apertures by means of the shutters, it will be possible 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 produce, as 

 already mentioned, the image of an artificial coloured star. 



A new and very interesting microscopical object has recently 

 been added to the available novelties for the cabinet. Mr. J. B. 

 Dancer has made the curious discovery, that when the ash or dust 

 which collects in the flue of a furnace is examined under the micro- 

 scope with a power of 40 or 50 diameters, it is found to consist of 

 ferruginous matter and crystallized substances, some particles trans- 

 parent, others white and red. It contains also a number of curious- 

 looking objects, which vary considerably in size and colour; the 

 majority of these bodies are spherical, and when separated from the 

 irregularly shaped particles forming the bulk of the dust, they 

 become interesting objects for the microscope. Some are as perfect 

 in form as the most carefully turned billiard balls, and have brilliant 

 polish. Some are transparent crystal spheres ; others are opaque 

 white ; many are yellow and brown, and variegated like polished 

 agates or cornelian of different shades. There are others which 

 look like rusty cannon balls ; some of these have an aperture in 

 them like a bombshell, and many are perforated in all directions. 



vol. rv. 2 o 



