90 



POPULAR FALLACIES. 



from the body. In fact, the glass will only feel cold to the touch for a short 

 space of time after it is first touched. The same observation will apply to por- 

 celain and other bodies which are bad conductors, and yet which are dense 

 and smooth. On the other hand, a mass of metal, when touched, will continue 

 to be felt cold for any length of time, and the hand will be incapable of warm- 

 ing it, as was the case with the glass. 



A silver or metallic teapot is never constructed with a handle of the same 

 metal, while a porcelain teapot always has a porcelain handle. The reason of 

 this is, that metal being a good conductor of heat, the handle of the silver or 

 other metallic teapot would speedily acquire the same temperature as the water 

 which the vessel contains, and it would be impossible to apply the hand to it 

 without pain. On the other hand, it is usual to place a wooden or ivory han- 

 dle on a metal teapot. These substances being bad conductors of heat, the 

 handle will be slow to take the temperature of the metal, and even if it does 

 take it, will not produce the same sensation of heat in the hand. A handle, 

 apparently silver, is sometimes put on a silver teapot, but, if examined, it will 

 be found that the covering only is silver ; and that at the points where the han- 

 dle joins the vessel, there is a small interruption between the metallic covering 

 and the metal of the teapot itself, which space is sufficient to interrupt the 

 communication of heat to the silver which covers the handle. In a porcelain 

 teapot, the heat is slowly transmitted from the vessel to its handle ; and even 

 when it is transmitted, the handle, being a bad conductor, may be touched with- 

 out inconvenience. 



A kettle which has a metal handle cannot be touched, when filled with boil- 

 ing water, without a covering of some non-conducting substance, such as cloth, 

 or paper, while one with a wooden handle may be touched without inconve- 

 nience. 



The feats sometimes performed by quacks and mountebanks, in exposing 

 their bodies to fierce temperatures, may be easily explained on the principle 

 here laid down. When a man goes into an oven, raised to a very high temper- 

 ature, he takes care to have under his feet a thick mat of straw, wool, or other 

 non-conducting substance, upon which he may stand with impunity at the pro- 

 posed temperature. His body is surrounded with air, raised, it is true, to a high 

 temperature, but the extreme tenuity of this fluid causes all that portion of it 

 in contact with the body, at any given time, to produce but a slight effect in 

 communicating heat. The exhibitor always takes care to be out of contact 

 with any good conducting substance ; and when he exhibits the effect produ- 

 ced by the oven in which he is enclosed, upon other objects, he takes equal 

 care to place them in a condition very different from that in which he, himself, 

 is placed ; he exposes them to the effect of metal or other good conductors. 

 Meat has been exhibited, dressed in the apartment with the exhibitor : a metal 

 surface is, in such a case provided, and probably heated to a much higher tem- 

 perature than the atmosphere which surrounds the exhibitor. 



But although the sense of touch be, perhaps, the most exposed to have its 

 impressions misinterpreted, it is not the only sense which affords examples of 

 striking popular fallacies. Abundance of these are offered in the case of the 

 sense of sight. 



Every one is familiar with the appearance of the sun and moon when rising 

 and setting. The apparently large orb which they present to the senses is an 

 object of familiar notice. Is not every one impressed with a conviction that 

 the apparent magnitude of the sun when it rises, glowing with a redness ac- 

 quired from the depth of air through which its rays then pass, is much greater 

 than the apparent magnitude of the same object at noonday ? and is not the 

 same impression admitted with respect to the rising or setting full moon, com- 



