»4 



NATURE 



\_Xov. 6, 1S79 



slight one, and we fear it is still on the increase. " Unless," 

 said Mill, " individuality shall be able to assert itself 

 against the yoke of public opinion, Europe, notwithstand- 

 ing its noble antecedents and its professed Christianity, 

 will tend to become another China." Prof. Miiller would 

 persuade us that our Universities are a safeguard against 

 this catastrophe. But when China is mentioned in con- 

 nection with education, examinations are suggested by an 

 irresistible association. If, therefore, England is to 

 escape the fate of China, it is not only encouraging to 

 reflect that the most conspicuous modern building in 

 Prof. Midler's own University is the new Examination 

 Schools. 



DESCRIPTION OF AN INSTRUMEN1 FOR 

 EXPLORING DARK CA V1TIES WHICH ARE 

 INACCESSIBLE TO DIRECT LIGHT 



AN electric lamp has recently been proposed for 

 surgical and dental operations. 1 Some years ago I 

 designed an instrument for illuminating the dark cavities 

 of the body which would, I think, be very serviceable in 

 connection with an electric lamp. 



This instrument consists of a series of prisms arranged 

 somewhat as in the corona employed for spectrum analysis. 

 The accompanying woodcut will be sufficiently intelligible 



o 



-without any detailed description. The different prisms 

 are of glass of such refractive indices as to secure achro- 

 matism, and the rays of light are bent round corners, so 

 as, finally, to reach an external observer. 



In most cases one or two such prisms will be sufficient, 

 but any number may be employed so long as the loss of 

 light from absorption, superficial reflection, and other 

 causes is not so great as to defeat the object in view by 

 destroying the distinctness of the image. 



Thomas Stevenson 



1 Engineer, March, 1879. 



IMPROVEMENTS IN BLEACHING 



A METHOD of applying the ordinary bleaching agents 

 (hypochlorites) in a new way has been invented by 

 Count Dienheim de Brochocki of Paris. Instead of im- 

 mersing the goods to be bleached in an ordinary "chloride 

 of lime" vat, and subsequently souring, the inventor 

 treats bleaching-powder with an acid and simultaneously 

 passes air through the mixture, so that chlorine and 

 hypochlorous acid vapours are mechanically carried off; 

 the resulting gases are passed through an alkaline solution 

 in such proportions as to saturate part or the whole of the 

 alkali, or to supersaturate it at will. The resulting liquid 

 is said to be sufficiently stable to be kept without change 

 for two or three months ; it can readily be prepared of a 

 density of 30 Beaumd, and acts as a bleacher without 

 requiring any acidulation, and for many purposes is said 

 to be superior to the ordinary bleaching-vat. 



To this liquid the fanciful name "chlorozone" has been 

 given, the inventor asserting that the oxidising power of 

 a given quantity of bleaching-powder is increased by this 

 treatment through the fixation in the product of some of 

 the oxygen of the air used as carrying agent ; the which 

 oxygen he conceives to be liberated in the form of ozone 

 in contact with the goods to be bleached ! Although no 

 experimental proof of the truth of this somewhat novel 

 proposition appears to have been vouchsafed to the 

 scientific world, yet it would seem that the new product 

 has at least some practical advantages over the older 

 bleaching agents, as it is used to a considerable extent in 

 Paris, whilst works for its manufacture on a large scale 

 have been recently erected at Warrington by Messrs. 

 Nath. Holmes and Partners. 



HERI.XG'S THEORY OF THE VISION OF 



LIGHT AND COLOURS 1 



III. 



IN the sixth and last memoir the author develops the 

 part of his theory which has probably excited the most 

 interest, namely, that of the vision of colours. He devotes 

 his first section to the mode of classification of colours, 

 and as this is not only the most important part, but differs 

 materially from the generally received views, it is desirable 

 to give its substance pretty fully. 



He explains that, as he has based his general theory on 

 what are naturally and physiologically two simple sensa- 

 tions, white and black, so he proposes to base his treat- 

 ment of colours on the "natural system of colour- 

 sensations." He then has to seek what the simple natural 

 sensations of colour are, neglecting in this classification 

 all consideration of the physical properties usually con- 

 nected with them. He inquires, therefore, what simple 

 colour-sensations there are. Taking the six usually ad- 

 mitted, violet, blue, green, yellow, orange, and red, he 

 finds that two, namely, violet and orange, are obviously 

 compound sensations ; for in violet of every hue there 

 can be distinguished clearly a mixture of the two sensa- 

 tions, blue and red ; and similarly in orange there can 

 always be traced the elements of red and yellow. The 

 other four colours are red,' 2 green, blue, and yellow. None 

 of the sensations known by these names contain, when 

 pure, any semblance of another colour-sensation. These 

 four, therefore, may with perfect correctness, as was 

 pointed out by Leonardo da Vinci, be considered as simple 

 or fundamental colour- sensations. On this account they 

 have received special names, not borrowed from any 

 coloured natural objects. 



All other colour-sensations than these may be called 

 mixed or compound sensations, as two elements can 

 always be discovered in them ; but it is a fixed principle 



1 Continued from 

 " This, however, 

 yellow. 



