Mr. Ivory 07^ the Constitution of the Atmosphere. 249 



in this atmosphere will agree with the mean result deduced 

 from the experiments recorded by Ramond. 



We may now generalize the conclusion at which we have 

 just arrived. — Every atmosphere in which the laws of elastic 

 fluids are observed, and in which the initial gradation of heat 

 is made to coincide with that which obtains at the earth's sur- 

 face, will represent terrestrial experiments taken at a mean 

 with sufficient accui-acy. Unless we can push our experi- 

 ments to heights in the atmosphere hitherto inaccessible, or 

 remove the accidental irregularities of the thermometrical ex- 

 periments in that part of it withui our reach, it may be said 

 that the present research is brought to a conclusion. Many 

 atmospheres may be found in which the pressure, the tem- 

 perature, and the density, shall agree with nature in a mean 

 of many experiments. 



The same atmospheres likewise represent the astronomical 

 refi-actions with considerable accuracy. In this respect they 

 agree with one another and with nature, unless at very low 

 Jiltitudes. Even the horizontal refractions are not much dif- 

 ferent in the several cases, and approach nearly to the quan- 

 tity found by observation, — if indeed we can affirm any thing 

 of an element hitherto ascertained with so little precision. But 

 the atmospheres vary more from one another in the celestial, 

 than in the terrestrial, pheenomena. In the one case, the light 

 of a star traverses the whole of the earth's atmosphere ; in the 

 other, our experiments are confined to a very limited altitude. 

 It is sufficient for the terrestrial phenomena, that an atmo- 

 sphere coincide with that of nature in its lower part ; but the 

 astronomical refractions require that both coincide neax'ly in 

 their whole extent. 



Of all the atmospheres which agi'ee with terrestrial experi- 

 ments, that determined by the equations (a), in which the gra- 

 dation of heat is equable, must diverge soonest, and in the 

 greatest degree, from the earth's atmosphere in which the 

 height requisite for depressing the thermometer a given quan- 

 tity continually increases in ascending. The atmosphere de- 

 termined by the equations (d) is preferable ; because the rate 

 of the decrease of heat becoming gradually slower, the coinci- 

 dence with nature nuist reach to a greater extent. In reality, 

 if the refractions computed from the equation (a) and (d) be 

 compared with the quantities determined by observation, al- 

 though there will be found almost an exact coincidence to a 

 great distance from the zenith, yet the errors of the former 

 become considerable sooner, or at greater altitudes, than those 

 of the latter. 



Vol, GG. No. 330. Oct. 1825. I i In 



