4 i4 



Progress in Science. 



[July, 



in free state present, and the tubes exposed to light, a mechanical change 

 is effected, since the previously crystalline salts — obtained in that state from 

 the ammoniacal solutions of the chloride and bromide and hydriodic acid 

 solution of the iodide of silver — become at first dull, and next crumble 

 to powder. This mechanical change of the haloid salts of silver is greatest 

 when'the chemical change is smallest. 



The change produced in animal and vegetable forms by the influence of 

 varying conditions of temperature, moisture, light, locality, &c, has induced 

 many persons to try experiments on the influence of colour on insects, 

 from which some interesting results have been derived. In some of these 

 experiments, lately published, a brood of caterpillars of the tortoise-shell 

 butterfly was divided into three lots. One-third were placed in a photographic 

 room lighted through orange-coloured glass, one-third in a room lighted 

 through blue glass, and the remainder kept in an ordinary cage in natural 

 light. All were fed with their proper food, and the third lot developed into 

 butterflies in the usual time. Those in the blue light were not healthy, a 

 large number dying before changing ; those raised in the orange light, how- 

 ever, were nearly as healthy as those first mentioned. The perfed insect 

 reared in the blue light differed from the average form in being much smaller, 

 the orange-brown colours lighter, and the yellow and orange running into each 

 other instead of remaining distinct. Those raised in the yellow light were 

 also smaller, but the orange-brown was replaced by salmon-colour ; and 

 the blue edges of the wings seen in the ordinary form were of a dull slate. If 

 changes so great as these can be produced in the course of a single experi- 

 ment, it is probable that a continuance of the same upon a succession 

 of individuals would develop some striking results. 



By means of the equatorial refractor of 15 inches aperture, by Messrs. 

 Grubb and Son, recently placed in Dr. Huggins's hands by the Royal 

 Society, this eminent physicist has succeeded in making observations 

 described below of the remarkable spectrum which is afforded by the light 

 of the planet Uranus. The spectrum of Uranus, as it appears in this 

 instrument, is represented in the accompanying diagram. The narrow 



Fig. ii. 



2? 4& 4.4 SO Si 



(III II lllll I I I I I III I I I I 



E 

 liiiimi 



se sr 

 1 mill 



G3 C4 £5 66 



I. nil. ml. mill 



spectrum placed above that of Uranus gives the relative positions- of the prin- 

 cipal solar lines, and of the two strongest absorption-bands produced by 

 our atmosphere, namely, the group of lines a little more refrangible than d, 

 and the group which occurs about midway from c to d. The scale placed 

 above gives wave-lengths in millionths of a millimetre. The spectrum of 

 Uranus is continuous, without any part being wanting, as far as the feebleness 

 of its light permits it to be traced, which is from about c to about g. On 

 account of the small amount of light received from this planet, a slit suffi- 

 ciently narrow to bring out the Fraunhofer lines could not be used. The posi- 

 tions of the bands produced by planetary absorption, which are broad and 

 strong in comparison with the solar lines, were determined by the micrometer 



