BLU 



BLU 



scurf from it; then heat it. in the fire, 

 and as it grows hot the colour changes 

 by degrees, coming- first to a light, then 

 to a dark g-old colour, and lastly to a 

 blue. Sometimes they grind also indigo 

 and sallad oil tog-ether, and rub the mix- 

 ture on the work with a woollen rag 

 while it is heating 1 , leaving- it to cool of 

 itself. Among- sculptors we also find men- 

 tion of bluing a figure of bronze, by which 

 is meant the heating- of it to prepare it 

 for the application of g-old leaf, because 

 of the bluish cast it acquires in the ope- 

 ration. 



BLUENESS, that quality which deno- 

 minates a body blue, depending on such 

 a size and texture of the parts that com- 

 pose the surface of a body, as dispose 

 them to reflect the blue or azure rays of 

 light, and those only, to the eye. 



With respect to the blueness of the 

 sky, M. de la Hire, after Leonardo da 

 Vinci, observes, that any black body, 

 viewed through a thin white one, gives 

 the sensation of blue ; and this lie assigns 

 as the reason of the blueness of the sky, 

 the immense depth of which, being- whol- 

 ly devoid of light, is viewed through the 

 air, illuminated and whitened by the sun. 

 l-'or the same reason, he adds, it is, that, 

 soot mixed with white makes a blue ; for 

 white bodies, being always a little trails- 

 parent, and mixing themselves with a 

 black behind, give the perception of blue, 

 t'rom the same principle he accounts for 

 the blueness of the veins. on the surface 

 of the skin, though. the blood they are 

 filled with be a deep red ; for red, he ob- 

 serves, unless viewed in a clear, strong- 

 light, appears a dark brown, bordering oil 

 black : being then in a kind of obscurity 

 in the veins, it must have the effect of a 

 black ; and this, viewed through the 

 membrane of the vein and the white skin, 

 will produce the perception of blueness. 



In the same way did many of the early 

 writers account for the phenomenon of a 

 blue sky ; but, in the explanation of this 

 phenomenon, Sir Isaac Newton observes, 

 that all the vapours, when they begin to 

 condense and coalesce into natural parti- 

 cles, become first of such a big-ness as to 

 reflect the azure rays, before they can 

 constitute clouds of any other colour. 

 This, therefore, being the first colour 

 which they begin to reflect, must be that 

 of the finest and most transparent skies, 

 in which the vapours are not arrived to a 

 grossness sufficient to reflect other co- 

 lours. 



M. Bouguer, without having recourse 

 to the vapours diffused through the at- 



mosphere, in order to account for the re- 

 flection of the blue-making' rays, ascribe 

 t it to the constitution of the air itseii; 

 whereby these fainter coloured rays arc 

 incapable of making their way through 

 any considerable tract of it : a'nd he ac- 

 counts for those blue shadows, which 

 were first observed by M. Buffo n in the 

 year 1742, by the aerial colour of the at- 

 mosphere, which enlig-htens these sha- 

 dows and in which the blue rays prevail ; 

 whilst the red rays are not reflected so 

 soon, but pass on to the remoter regions 

 of the atmosphere. 



The Abbe Mazeas, in a Memoir of the 

 Society in Berlin, for the year 1752, ac- 

 counts for the phenomenon of blue sha- 

 dows, by the diminution of light ; having- 

 observed, that of two shadows which weiM 

 cast upon a white wall, from an opaque 

 body illuminated by the moon, and by a 

 candle at the same time, that which was 

 enlightened by the candle was reddish, 

 and that which was enlightened by tho, 

 moon was blue. However, the true caus 

 of this appearance seems to be that as- 

 signed by M. Bouguer, which agrees with 

 the solution given, of it about the same 

 time by Mr. Melville. But, instead of 

 attributing the different colours of the 

 clouds, as Sir Isaac Newton does, to the 

 different size of those g-lobules into which 

 the vapours are condensed, Mr. Melville 

 supposes, that the clouds only reflect and 

 transmit the sun's light ; and that, ac- 

 cording to their different altitudes, they 

 may assume all the variety of colours at 

 sun-rising and setting, by barely reflecting- 

 the sun's incident light, as they receive it 

 through a shorter or longer tract of air ; 

 and the change produced in the sun's rays 

 by the quantity of air through which they 

 pass, from white to yellow, from yellow 

 to orange, and lastly to red, may be mi-, 

 derstood agreeably to this hypothesis, by 

 applying to the atmosphere what Sir Isaac 

 Newton says concerning the colour of 

 transparent liquors in general, and that 

 in the infusion -of lignum nephriticum in 

 particular. 



BLUSHING, a suffusion or redness of 

 the cheeks, excited by a sense of shame, 

 on account of a consciousness of some 

 failing or imperfection. 



Blushing is supposed to be produced 

 from a kind of consent or sympathy be- 

 tween the several parts of the body, oc- 

 casioned by the same nerve being extend- 

 ed to them all. Thus, the fifth pair of 

 nerves being branched from the brain to 

 the eye, ear, muscles of the lips, cheeks 

 and palate, tongue syud nose, a thing- 



