1819.] Prtf- Leslie oh Heat and Climate. 19 



expert slinger. If larger numbers be taken, such as 1000, 

 1500, and 2000 feet a second, the corresponding condensa- 

 tions of the air on the flat surface of the body will be found 

 to be "5564, 1*2520, and 2*2258, and the augmentations of 

 temperature 51°, 91°, and 135°. The celerity communicated 

 by fire-arms is generally 1,500 feet per second, sometimes 2000. 



These deductions apply accurately in the case of thin cylin- 

 ders ; but the effects must be somewhat diminished with globes, 

 since the air being displaced by an oblique stroke will not sutler 

 so much condensation. Were the discussion of sufficient 

 importance, an approximation might be found for the precise 

 change of temperature. But an objection occurs that appears 

 to have some weight. Is not the rarefaction of the air on the 

 posterior surface of the ball equal to the condensation on the 

 anterior? And if so, will not the cold produced on the one 

 hemisphere compensate for the heat extricated on the other? 

 I answer that the air behind follows the motion of the body ; 

 while that before is incessantly succeeded by other portions ; so 

 that the heating is permanent, and the cooling is only moment- 

 ary. The rotatory motion common to projectiles will not in the 

 least affect the operation of these causes. We must not, how- 

 ever, suppose that the heat will receive perpetual additions ; 

 there will be a certain standard of temperature corresponding to 

 the velocity of the body, and which it can never surpass. This 

 extreme point will be sooner attained by small balls than by 

 large ones, because the former have a greater surface in propor- 

 tion to their quantity of matter. The huge masses hurled from 

 the mouth of a cannon may not acquire the just increase of 

 temperature in the whole of their track. 



I shall now proceed to investigate the diversity of tempera- 

 ture which obtains at different latitudes and at different heights 

 of the atmosphere. I am sensible that on the first of these 

 inquiries, my speculations are very imperfect ; but I shall at 

 least develope the principles which ought to enter into the com- 

 putation. Were the theory of the motion of fluids tolerably 

 complete, the absolute quantities might be assigned. However, 

 ho vast is the intricacy of this department of science, that I 

 despair of ever seeing it arrive at such perfection. 



The theory of central fire has been consigned to oblivion, and 

 the heat of the earth ascribed wholly to the rays received from 

 the sun. We might thence infer that our globe is growing con- 

 tinually warmer. There are data even from which the quantity 

 of this increase of temperature can be determined. The mean 

 density of the earth is above four times that of water, as my 

 friend Dr. Hutton has deduced by ingenious and elaborate cal- 

 culations from the observations made on the mountain Shehal- 

 lien. This great density aftbrds a strong presumption that the 

 globe which we inhabit is composed principally of some metallic 

 oxide, most probably that of iron. But the rust of iron is three 



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