THE RAINBOW. 39 



injury is not often a benefit, which appears to us injurious 

 only because we do not understand it fully, every disturbing 

 cause tends to produce some apparent disorder, such as 

 storms, hurricanes, &c., some indeed so terrific as to destroy 

 ships and houses, but what would be the result if the 

 atmosphere were never disturbed from any cause P Why 

 the lower stratum would become so loaded with impurities 

 that it would be unfit to breathe, miasms and noxious gases 

 would for ever remain a curse to the races of men and 

 animals who might be doomed to inhabit such regions, but 

 the very regions where these miasms are most likely to 

 form are those about the tropics, and here it is that the 

 greatest storms occur to remove them. Even the great 

 deserts, which appear so useless to man, and which are 

 uninhabitable to a great extent, have their office, and an 

 important one too ; they are to the earth what ventilators 

 are to buildings, drawing the cold air from the poles to cool 

 the regions that are too hot, and sending a current of heated 

 air through the upper regions of the atmosphere (where 

 it can do no injury to anything) to warm the colder parts 

 of the earth, another instance of the wonderful care and 

 goodness on the part of the Creator. The various and 

 beautiful colours of the clouds, particularly at the rising 

 and setting of the sun, are caused by refraction separating 

 the white light into its primitive constituents, blue, red, 

 and yellow light and their combinations, purple, orange, 

 green, &c., and the more obliquely the rays impinge upon 

 the earth the greater will be this refraction, this accounts 

 for colours seldom appearing in the clouds at midday. But 

 of all the beautiful effects of the refraction of light, the 

 Rainbow (fig. 9) is the most glorious, it has been cele- 

 brated in all ages for its transient beauty. It is only seen 

 when rain is falling in front of a brightly illuminated cloud, 

 the sun being behind the spectator ; it is a reflection of the 

 sun by the cloud transmitted through millions of drops of 

 rain, each of which acts as a prism, and produces rings of 

 colour ; for each of the rays of light (red, blue, and yellow) 

 are refracted in unequal degrees, and therefore take separate 

 places, forming the rings of colour seen in the rainbow. 



