80 



ON THE GENERAL DIFFUSION OF KNOWLEDGE. 



tion PCH is less than its angle of incidence 

 EGA. AE is the sine of the angle of inci 

 dence, and HP the sine of the angle of refrac 

 tion ; and the proportion they bear to each other 

 is as four to three. If a small body, therefore, 

 were placed at H and viewed from the point A, 

 ft would appear as if it were raised to the point 

 B, or one-fourth higher than it really is. 



This may be farther illustrated by the follow 

 ing common experiment. Put a shilling into the 

 bottom of an empty bason, at C , and walk back 

 wards till it appear completely hid by the inter 

 ception of the edge of the bason ; then cause 

 water to be poured into the bason, and the shil 

 ling will instantly appear as if placed at the 

 point D ; for, being now in a denser medium, 

 it appears raised, or nearer to its surface. Be 

 fore the water was poured in, the shilling could 

 not be seen where it was ; now it is seen where 

 it is not. It is not the&quot; eye that has changed its 

 place, but the ray of light has taken a new di 

 rection, in passing from the water to the eye, 

 and strikes the eye as if it came from the piece 

 of money. This experiment may be varied as 

 follows : Take an empty bason, and, along the 

 diameter of its bottom, fix marks at a small dis 

 tance from each other, then take it into a dark 

 room, and let in a ray of light ; and where this 

 falls upon the floor, place the bason, so that its 

 marked diameter may point towards the win 

 dow, and so that the beam may fall on the mark 

 most distant from the window. This done, fill 

 the bason with water, and the beam which be 

 fore fell upon the most distant mark, will now, 

 by the refractive power of the water, be turned 

 out of its straight course, and will fall two or 

 three or more marks nearer the centre of the 

 bason. 



It is owing to the circumstance now stated, 

 that an oar partly in and partly out of the water 

 appears broken ; that objects appear distorted 

 when seen through a crooked pane of glass ; that 

 a fish in the water appears much nearer the sur 

 face than it actually is ; and that a skilful marks 

 man, in shooting at it, must aim considerably 

 below the place which it seems to occupy. It 

 is owins to (lie refractive power of the atmos 

 phere, that the sun is seen before he rises above 

 the horizon in the morning, and after he sinks 

 beneath it in the evening ; that we sometimes 



see the moon, on her rising, totally eclipsed, 

 while the sun is still seen in the opposite part of 

 the horizon ; and that the stars and planets are 

 never seen in the places where they really are, 

 except when they are in the zenith, or point di* 

 rectly over our head. 



Many affecting and fatal accidents have hap 

 pened, and are frequently recurring, particu 

 larly to children, and females in the higher ranks 

 of life, from their clothes catching Jire, most of 

 which might be prevented, were the two follow 

 ing simple facts universally known and practi 

 cally applied, that flame has a tendency to mount 

 upwards; and that air is essentially requisite for 

 supporting it. When the clothes of females 

 take fire, as the fire generally begins at the 

 lower parts of their dress, so long as they con 

 tinue in an upright posture the flames naturally 

 ascend, and meeting with additional fuel as 

 they rise, become more powerful in proportion ; 

 whereby the neck, the head, and other vital 

 parts of the body are liable to be most injured ; 

 and, by running from one part of the room to 

 another, or from one apartment to another, as is 

 most frequently the case, the air, which is the 

 fuel of fire, gains free access to every part of 

 their apparel, and feeds the increasing flame. 

 In such cases, the sufferer should instantly 

 throw her clothes over her head, and roll or lie 

 upon them, in order to prevent the ascent of the 

 flames and the access of fresh air. When this 

 cannot conveniently be effected, she may still 

 avoid great agony, and save her life, by throw 

 ing herself at full length on the floor, and rolling 

 herself thereon. Though this method may not, 

 in every case, completely extinguish the flame, 

 it will to a certainty retard its progress, and pre 

 vent fatal injury to the vital parts. When as 

 sistance is at hand, the by-standers should im 

 mediately wrap a carpet, a hearth-rug, a great 

 coat, or a blanket, around the head and body of 

 the sufferer, who should be laid in a recumbent 

 position, which will prove a certain preventive 

 from danger. During the year 1813, the author 

 noted down more than ten instances, recorded 

 in the public prints, of females who were burned 

 to death by their clothes catching fire, all of 

 which might have been prevented, had the sim 

 ple expedients now stated been resorted to and 

 promptly applied. 



It may be remarked, in the next place, that 

 many of the diseases to which mankind are sub 

 ject particularly fevers, smaL-pox, and other 

 infectious disorders might be prevented by the 

 diffusion of knowledge in relation to their na 

 ture, their causes, and the means of prevention. 

 It cannot have been overlooked, in the view of 

 the intelligent observer, that fevers and other 

 infectious disorders generally spread with the 

 greatest facility and make the most dreadful 

 havoc among the lower orders of society. This 

 is owing, in part, to the dirty state in which 



