Thermometer, why does it indicate degrees of heat, 710
Thermometer, why are there Reaumur's and Fahrenheit's, 711
Thermometer and barometer, what is the difference, 712
Thermometer, in what season of the year does it vary most, 715
Thunder-peal, why is it sometimes loud and continuous, 616
Thunder-peal, why is it sometimes broken and unequal, 617
Thunder-peal, why is it sometimes a low, grumbling noise, 618
Thunder-peal, why does it sometimes follow immediately after the flash of lightning, 620
Thunder, through what distance will the sound travel, 621
Toasting-fork, why has it a wooden handle, 124
Tops, why do they stand erect while they spin, but fall when they stop, 814
Touch, in what part of the body is the sense of most perfect, 1005
Trap and ball, why is the ball propelled upward, when the trigger is struck, 866
Trees, what are the estimated ages of, 1214
Trees, what are the northern limits of, 1237
Trees, why are they covered with bark, 1270
Trees, why have those with large trunks a great number of leafy branches, 1274
Trees, why have poplars comparatively few leaves, 1275
Trees, why had the mammoth comparatively few leaves, 1276
Trees, why have oaks an abundance of leaves, 1277
Trees, why are their trunks generally round, 1278
Vacuum, is it possible to obtain a perfect, 650
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 distribution of, 1208
Vegetation, what are the characteristics of tropical, 1218
Vegetation, what are the changes in on quitting the tropics, 1232
Vegetation, what are the characteristics of, upon approaching the polar zones, 1234
Vegetation, what are the characteristics of mountain, 1238
Vines, where are their favourable climates, 1233
Water, what becomes of that formed by combustion, 58
Water, is it a good or bad conductor of heat, 151
Water, why, when a blacksmith thrusts a hot iron into a tank, do we perceive a peculiar smell, 309
Water, how many degrees of latent heat are hidden in its several states, 327