28 Mr. Darnell's Reply to Z. [Jan. 



sequence of any degree of projectile motion that might be com- 

 municated to it. It is not for me to surmise in what way it can 

 have been possible for your correspondent to confound together 

 pressure and gravitation, but certain it is that the planets do 

 not press upon the sun, nor the moon upon the earth. It is no 

 less certain that all the particles of the atmosphere do press upon 

 the earth, and, like the waggon upon the road, the vessel upon 

 the water, or the cannon ball in the air, their weight is in no 

 degree dependant upon their motion or rest. 



These are the only objections brought forward by Z against 

 my theory of the Constitution of the Atmosphere ; but he 

 " suggests that the third table in Part I. is founded-upon an 

 erroneous principle." In reply to this, I must observe that the 

 tables in this part of my work were not meant to be accurate 

 representations of the different states of the atmospheric columns, 

 but mere rough approximations ; and their use is to assist the 

 mind in following the train of reasoning in the same way that 

 rudely-sketched diagrams assist the mathematician in solving a 

 problem of Euclid. The principle upon which they were con- 

 structed is this : I assumed the mean temperature of the latitude 

 for which I wished to calculate the atmospheric column as the 

 temperature of an homogeneous atmosphere ; and I thence 

 derived the pressures at different altitudes from the surface, and 

 from these the regular decrease of temperature for the density. 

 It is clear that for accurate purposes, both the pressures and 

 temperatures so obtained require correction, and that the tables 

 include an error which should be divided between the two, and 

 does not fall wholly upon the pressure as suggested by Z. The 

 labour of applying these corrections would have been very con- 

 siderable; and the tables, which, even in their present state, 

 cost me much pains, would not have better answered the pur- 

 poses of illustration. 



In conclusion, I cannot but express my acknowledgments to 

 Z for the general courtesy of his review, but am still inclined to 

 appeal from his tribunal ; for I must own that my ambition 

 cannot yet content itself with the somewhat meagre consolation 

 which has been offered to me, that " there can be no discredit 

 to any one who fails to unfold the causes of phenomena which 

 have been acknowledged by one of the first philosophers of 

 the present times to have hitherto baffled all attempts to reduce 

 them to fixed principles." 



I remain, dear Sir, yours most faithfully, 



J. F. Daniell. 



