QUESTIONS FORMING A COMPLETE INDEX. 



XXV 



LESSON LXXIII. 



Trees, why have those with large 

 trunks a great number of leafy 

 branches , ... 1274 



Trees, why have poplars compara- 

 tively few leaves 1275 



Trees, why had the mammoth com- 

 paratively few leaves 1276 



Trees, why have oaks an abun- 

 dance of leaves 1277 



Trees, why are their trunks gen- 

 erally round 1278 



Twilight, what is the cause of ... 482 



Vacuum, what is a 649 



Vacuum, is it possible to obtain a 

 perfect 650 



Vegetables, have they any heat ... 90 



Vegetable structures, of what do 

 they consist 1151 



Vegetables, why do farmers sow 

 different crops in rotation ... 1164 



Vegetables, why are the hearts of 

 cabbages, &c., pale yellow ... 1182 



Vegetable productions, why are 

 they so widely diffused ... ... 1189 



Vegetable eaters, why do they feed 

 so continually 1091 



Vegetation, geographical distribu- 

 tion of 1208 



Vegetation, what are the character- 

 istics of tropical 1218 



Vegetation, what are the changes 

 in on quitting the tropics. ... 1232 



LESSON LXX1V. 



Vegetation, what are the character-' 

 istics of, upon approaching the 

 polar zones 1234 



Vegetation, what are the charac- 

 teristics of mountain 1238 



Vines, where are their favourable 

 climates ,., 1233 



Walking, why does it make us 

 warmer ., 26 



Water, what becomes of that 

 formed by combustion ... ... 58 



Water, is it a good or bad conduc- 

 tor of heat 151 



Water, why does it extinguish fire 306 



Water, why, when a blacksmith 

 thrusts a hot iron into a tank, do 

 we perceive a peculiar smell ... 309 



Water, why does it freeze 324 



Water, why does it become steam 326 



Water, how many degrees of lat- 

 ent heat are hidden in its several 

 states 327 



Water, why does it expand when 

 freezing, while bodies generally 

 contract with cold and expand 

 with heat 341 



Water, why does it never freeze 

 to a great depth 342 



Water, how much deeper is it than 

 it appears to be ... . 480 



2 



LESSON LXXV. 



Water, why has the exceptional 

 law, by which it expands when 

 free/in?, been ordained 343 



Water, why can we seldom suc- 

 ceed in the first attempt to touch 

 anything lying at tho bottom of 481 



Water, what causes it to flow from 

 a pump 651 



Water, why does it run through a 

 syphon 655 



Water, what is it 748 



Water, why does it become solid 

 when it freezes 751 



Water, why does it boil 753 



Water, what proportion of the 

 earth's surface is covered by it 554 



Water, why does it dissolve sub- 

 stances 758 



Water, why does hot dissolve more 

 readily than cold 759 



Water, why is it sometimes hard 7fiO 



Water, why is rain-water soft ... 761 



Water, why is it difficult to wash 

 in hard 763 



Waters, why are some impreg- 

 nated with mineral matters ... 767 



Water, why does stagnant become 

 putrid 769 



Water, is there danger attending 

 drinking it on account of animal- 

 cules 770 



Water, what are the means by 

 which it may be purified 771 



LESSON LXXVI. 



Water, what is the pressure of ... 775 



Water, why will a drop upon the 

 blade of a knife leave a dark spot 777 



Water, why does it roll in agitated 

 globules when dropped upon hot 

 iron 796 



Water, why does oil float upon it... 797 



Water, why is spring fresh and in- 

 vigorating 803 



Water, why is boiled flat and in- 

 sipid 804 



Weather, why does a yellow sun- 

 set foretell wet 534 



Weather, why does a red sunset 

 foretell fine 535 



Weather, why does a red sunrise 

 foretell wet 536 



Weather, why does a grey sunrise 

 foretell dry 537 



Weather, barometrical indications 

 of , 708 



Whales, why have they a large de- 

 velopment of oily matter about 

 their heads 1058 



Whale, why has it feathery bones 

 extending from its jaws 1095 



Whales, why are their eyes pro- 

 vided with very thick coats ... 1131 



Wheat, why do the ears stand up 

 by day and turn down by night.. 1175 



Wheat, what is it ... 1198 



