Dr CoJquhoun on the Argillaceoiis Ore of Iron. 67 



No. of sets 

 of observation. 



Mean temp. eq. from Ceylon observation 5 80® 66 



Batavia do. 4 81 08 



Hawai do. 1 79 67 



Malay Peninsula do. 3 79 42 



The mean of which, taking into account the 



number of observations in each set, is - 80° 44> 



We may therefore safely conclude from these results, that 

 in fixing the mean temperature of the equator at 81 1°, Ba- 

 ron Humboldt has exhibited that sagacity which characte- 

 rizes all his researches; and that the climateric formulae in which 

 we have adopted his determination represent better than any 

 other the great mass of observations which have been made in 

 the different parts of the globe. Even if the observations at 

 Pondicherry * were made with care, and at those times of the 

 day which give the mean daily temperature, it would be un- 

 philosophical to regard such a solitary example of high tem- 

 perature as affecting, in the slightest degree, general results de- 

 duced from numerous observations, made at various and distant 

 points of the equinoctial zone. 



Aet. XIII. — A Metallurgic Memoir on the Nature and 

 History of the Argillaceous Carbonate of Iron. By Hugh 

 CoLauHouN, M. D. Communicated by the Author. (Con- 

 tinued from vol. vii. p. 242.) 



These are the general mineralogical features which distinguish 

 the ironstone. We shall now proceed to divide the subspecies 

 into its principal varieties. 



1. Common Compact Argillaceous Carbonate of Iron. This 

 is the general type of the species, and, as such, the extreme 

 variations of which it is susceptible in colour, fracture, texture, 

 and hardness, have been already noticed. It is sometimes so 

 much impregnated with bituminous matter, that its external 



• Its mean temperature is stated at 85°.28'. 



L 



