NATURAL PHILOSOPHY. 153 



of his range. This continued from eleven o'clock to about three, 

 within which hours bread could not be baked. With the decline 

 of the sun in the afternoon, as in the early morning, tlie oven pei'- 

 formed its office better. The chimney was fifty-four feet high ; 

 the roof of the house was of dark slate, and it was all exjiosed to 

 heat before eleven ; some of it began to pass into shade about 

 three. 



In the eflFect of this greater exposui'e to the sun during the 

 hours when the sun is brightest. Prof. Horsford found the ex- 

 planation of the observed phenomenon. The heated top and 

 sides of the bouse warmed the air in contact, giving rise to an 

 upmoving column from the top of the house and to an endless 

 shroud of air sweeping up the sides of the house. This ascend- 

 ing shroud draws the air from the cracks, doors, and windows of 

 the house, lessening the pressure of the air in the interior, and, 

 of course, diminishing the di-aft. 



The following are his conclusions : — 



1. That sunshine, falling on the flame only of a burning body, 

 does not affect its rate of combustion. 2. That, other things 

 being equal, neither light nor darkness exerts appi'eciable in- 

 fluence on the rate of combustion. 3. That, other things being 

 equal, of two samples of the same combustible, one burning in 

 sunshine will consume more rajoidly than one burning in dark- 

 ness. 4. That combustion during the winter is more vigorous 

 than in summer, becaixse a given volume of air contains more 

 oxygen, is denser and dryer. 5. That slight currents, by causing 

 a flame to flare and come in contact with more air in a given 

 time, cause more rapid combustion ; and, by presenting greater 

 surface from which radiant heat issues to warm the combustible 

 about to burned, increase the rate of combustion. 6. That the 

 diminished draft of chimneys in very hot weather, when the 

 general atmosphere is at rest, and the sunshine intense, is due to 

 upward currents on the outside of the house, arising from the 

 heated surfaces of the roof and walls, which currents draw out- 

 ward through cracks, and open doors and windows, the air from 

 the interior of the house, and so lessen the pressm-e within, and 

 overcome the draft of the chimney. 7. That the popular imjjres- 

 sion that intense sunshine lessens the draft of chimneys is founded 

 in fact. — Scientific American. 



TRANSFORMATION OF MOTION INTO HEAT. 



Mr. Rennie has demonstrated in the most satisfactoiy manner 

 that this ti'ansformation takes place, even in the case of fluids. 

 He boiled an egg in six minutes by merely placing it in a vessel 

 which contained about ten pounds of water, and which was made 

 to revolve two hundred and thirty-two times in a minute. In 

 this case, motion was the only possible source of heat ; and the 

 result Avas the more striking, as the friction of fluids is so very 

 much less than that of solids. — Intellectual Observer, May, 1866. 



