396 Miscellaneous Intelligence. 



under which M. Plateau can see the different colours, are as fol- 

 lows: — 



The angles observed in sun-light are nearly a third of those in the 

 shade, iii. When the sensations of two different colours succeed 

 each other on the retina with a velocity less than that necessary to 

 make the two impressions appear as one, there generally appear 

 certain shades which are extraneous to the two colours employed, 

 or to their mixture ; by this means a fine white can be obtained 

 when the yellow and blue colours only are used. iv. When two 

 alternating sensations succeed each other with such rapidity that 

 they produce but one impression, the latter does not always present 

 a colour which would result from the mixture of the former ; thus, 

 combining the effect of yellow with that of deep blue in the way 

 just mentioned, a grey colour can be produced without the least 

 appearance of green, v. With the exception, perhaps, of yellow, 

 the sensations of certain colours do not act in their combination with 

 other sensations in the order of the intensity of their colours ; their 

 maximum of influence exists in a certain pale tint, on each side of 

 which their influence diminishes : thus, the blue colour of maximum 

 power with respect to red and yellow, is that of the sky in its most 

 coloured state. — Bull. Univ. A. xii. 123. 



7. Brewster's Monochromatic Lamp. — Dr. Brewster makes a mo- 

 nochromatic lamp by taking a portable gas lamp and fixing a platina 

 wire, or a plate of mica in the flame ; platina wire spirals answer 

 very well until they become covered with carbon. A large cotton 

 wick also, imbued with sal ammoniac, produces a good effect in a 

 hot gas flame. The supply of solution of muriate of ammonia, 

 required to continue the light, may be given by means of a large 

 sponge, or a capillary fountain. Dr. Brewster has used these mono- 

 chromatic lamps very much in microscopical researches. — Edin. 

 Jour. 



8. Artificial Magnets and their uses. — Extract of a letter from 

 Strasbourg: — Dr. Keil, of Langensalza, has discovered a method 

 of making artificial magnets of enormous force, and infinitely more 

 powerful than those as yet made, without great increase of dimen- 

 sions. He has also, by their means, cured many diseases depen- 

 dant upon the nervous system. The most powerful magnets as yet 

 made, have been large, and not supported more than 88 or 90 

 pounds ; but M. Keil has made one which sustains 45 pounds, and 

 yet weighs itself only 3 pounds 6 ounces ; he has another which 



