Lesson xxv.] LIGHT AND COLOURS. r63 



It may be observed, that Hack and while are 

 never reckoned among the primary Colours ; for 



the other colours less as they were lighter; and the quite 

 white remained on the surface of the snow, not having en- 

 tered it at all. 



" What signifies philosophy that does not apply to some 

 nse ? May we not learn from hence, that black clothes arc 

 not so fit to wear in a hot snnny climate, or season, as white 

 ones } because, in such clothes the body is more heated by 

 the sun when we walk abroad, and are at the same time 

 heated by the exercise, which double heat is apt to bring on 

 putrid dangerous fevers ? That soldiers and seamen who 

 must march and labour in the sun, should, in the East or West 

 Indies, have an uniform of white ? That summer hats for 

 men or women, should be white, as repelling that heat which 

 gives head-achs to many, and to some the fatal stroke that 

 the French call the Coup tie Soleill That the ladies' summer 

 hats, however, should be lined with black, as not reverberat- 

 ing on their faces those rays which are reflected upwards 

 from the earth or water ? That the putting a white cap of 

 paper or linen, within the crown of a black hat, as some do, 

 will not keep out the heat, though it would if placed without ? 

 That fruit walls being blacked ma> receive so much heat 

 from the sun in the day time, as to continue warm, in some 

 degree, through the night, and thereby preserve the fruit 

 from frosts, or forward its growth ? With sundry other parti 

 culars of less or greater importance, that will occur from time 

 to time to attentive mindsr" 



Many other properties of bodies of different Colours may 

 be found in various parts of Sir Isaac Newton's Optics. 



The subject of Light and Colours has been lately consider- 

 ed with much acuteness and attention by Mr. Delavel. From 

 a variety of well-conducted experiments this gentleman con- 

 cludes, that Colours are exhibited, not by reflected, but by 

 transmitted Light. For an ample investigation of this curious 

 and interesting subject, the reader must be referred to the 

 Memoirs of the Manchester Society, Vol. II. 



Hack 



