QUESTIONS FORSJING A COMPLKTE INDEX. 



LESSON LIII. 



Oxygen, whnt is it 25 



Oxygen of the air, why does it not 

 take fire 28 



Oxysjen, why do we know that it 

 will not burn of itself 29 



Oxygen, why do we know that it is 

 necessary to our existence ... 30 



Oxygen, where is it found " 31 



Oxygen, why is it mixed with ni- 

 trogen in the air ... ... ... 32 



Oxygen of water, why does it not 

 support fire 307 



Oxygen, in what wy does man 

 use it 757 



Ozone, what is it ... 630 



Ozone, why do we know that elec- 

 tricity produces it ... ... ... 631 



Ozone, what are the properties of 632 



Paleness, what is the cause of ... 914 



Palms, what are their characteris- 

 tics 1221 



Paper held over a candle-flame, 

 why does it become scorched ... 244 



Paper held below a candle-flame, 

 why does it scarcely become 

 warm 245 



Paper, why does it more readily 

 ignite than wood ... ... ... 29 1 



Paper, why, if it is laid flat upon 

 the fire, will it " char" before it 

 ignites 304 



LESSON LIV. 



Paper on a fire, why will it ignite 

 when you send a puff of air to 

 it 305 



Parachutes, why do they fall grad- 

 ually to the ground 834 



PaiTots, &.C., why have they crook- 

 ed bills 1047 



Parrots, why can they move their 

 upper as well as their lower 

 beak 1048 



Particles of matter, why do they 

 draw near each other 776 



Particles of matter, why will they 

 attach themselves to sealing-wax 

 excited by friction 779 



Pea and pin, why do they rotate 

 upon a jet of air blown through 

 a tobacco-pipe ... ... ... 845 



Peg-top, why does it make less 

 noise than a hurnming-top ... 811 



Pog-top, why does it sometimes 

 hum, arid at other times not ... 812 



Pelican, why has it a large pouch 

 uuder its bill 1093 



Pepper, where is it produced ... 1229 



Pt r-piration, why does it cool the 

 body 173 



Perspire, why do we ... ... 1009 



Perspiration, how is it formed ... 1010 



Perspiration, what is insensible ... 1011 



Perspiration, what is sensible ... 1012 



LESSON LV. 



Phosphorous, why does it look lu 

 minous 94 



Phosphorous, does it ignite sponta- 

 neously when placed upon a hot 

 surface 314 



Phosphorous, why does it ignite 

 when sprinkled with powdered 

 charcoal 315 



Photographic pictures, how does 

 light produce them 55G 



Photographic rooms, why are they 

 glazed with blue glass 557 



Pith-tumblers, why do they always 

 pitch on one end ... ... ... 868 



Planets, how can man weigh them 785 



Planets, how can man measure 

 their distances 786 



Plants, do they absorb heat ... 225 



Plants, how do we know that they 

 absorb heat 226 



Plants, why do screens prevent 

 frost from killing them 400 



Plants, why, if we cut across their 

 steins, do we see tubes arranged 

 in parallel lines 1159 



Plants, why do some droop and 

 turn to the earth after sunset ... 1167 



Plants, why are the seeds of 

 many enclosed in rich juice or 

 pulp 1172 



Plants, why have some tough curly 

 tendrils 1173 



LESSON LVI. 



Plants, why have peas tendrils, and 

 beans none 1174 



Plants, why have grasses, &c., joints 

 or knots in their stalks 1176 



Plants, what is the circulation of 

 sap in 1179 



Plants, why does their sap ascend 

 and descend 1180 



Plants, why do they suffer from 

 the smoke of cities 1188 



Plants, why is it understood that 

 some of them feel 1141 



Plants, why is it understood that 

 some of them move 114? 



Plants, of what elementary sub- 

 stances are they composed ... 1143 



Plants, whence do they derive their 

 elementary substances 1144 



Plants, how do they obtain carbon 1145 



Plants, how do they obtain oxygen 1146 



Plants, their decomposition ot gases 

 by day and by night 1147 



Plants, how do they obtain hydro- 

 gen ... , 1147 



Plants, how do they obtain nitrogen 1148 



Plants, how do they apply their ele- 

 ments to the formation of their 

 structures 1149 



Plants, how is their nutritive sap 

 applied to their growth and 

 nourishment 1150 



