246 Observations made at Port Macquarie. 



here soon, which my friend Mr Exshaw has procured for me. 

 I have a letter from him, dated the 30th January, in which 

 he says, " A discovery somewhat similar has been made at 

 Cadillac, fifteen miles above Bordeaux. It differs from the Lu- 

 nel cavern, 1 ' (that of the proprietaire,) " by the size being much 

 smaller, and by the species of bones found in it. With the ex- 

 ception of those of the hyena, (which are in great quantity,) 

 the others are of the herbivorous species, all bearing the evident 

 marks of being partly devoured by the hyena.'" 



Art. XIII. — Observations made at Port Macquarie, Van 

 Dieman's Land^for the purpose qf determining the Decrease 

 of Heat in Ascending in the Atmosphere. Communicated 

 to the Editor by Sir Thomas Brisbane, K. C. B. F. R. S. 

 Lond. & Edin. and Corresponding Member of the Acade- 

 my of Sciences of Paris. 



There is no department of meteorology less understood, and 

 at the same time more important, than that which relates to 

 the law of variation in the temperature of the atmosphere at 

 different heights. It is closely connected with the difficult 

 subject of astronomical refractions, and without its aid we can- 

 not reduce to the level of the sea the annual mean tempera- 

 tures of different points upon the earth's surface. 



It is generally assumed that the temperature decreases 1° 

 of Fahrenheit for every 300 feet that we ascend in the atmo- 

 sphere ; but this must vary not only with the mean tempera- 

 ture of the place, but with various circumstances in the rela- 

 tive situation of the two heights at which the observations are 

 made. If the lowest point is on a level plain, and the highest 

 in the free air, the decrease must be very different from what 

 it will be if the lowest point is the bottom, and the highest the 

 top of a mountain ; or if the observations are made at the low- 

 est and highest points of a great city ; or at the sea side, and 

 on the summit of a hill in the interior. In these different 

 cases a different law must prevail, and this law can only be 

 deduced from numerous and accurate sets of observations. 



Even in the first case, where the highest point is in the free 



