NOTES. 



and 462. In the course of the last 1? years, from some cause which lias not 

 been completely ascertained, the indications of the lower thermometer have 

 increased 0.220 ; but this probably is not due to any actual increase in the 

 general temperature of the caves. Results obtained by means of Artesian wells 

 are, indeed, liable to error, from infiltration, or from penetration from lateral 

 crevices; but currents of cold air, and other circumstances, are still more 

 injurious to the accuricy of the many laborious series of observations that have 

 been made in mines. The general result of Uoi-h's extensive examination 

 into the temperature of the mines in Snxony, gives a somewhat slower in- 

 crease of the terrestrial heat, or 1 C. to 41.84 metres (1 F. to 76.26 English 

 feet) Reich, Beob. iiber die Tcmperatur des Gesteins in verschiedenen 

 Tiefen, 1831, S. 13 4). Phillips, however, found, in the coal mine of Monk- 

 wearrnouth near Newcastle, in which, as I have already remarked, wordings 

 are carried on at a depth of nearly 1500 English feet below the level of the 

 sea, 32.4 metres, or 106.3 English feet to 1 C. (1 F. to 59.06 English feet), 

 a result almost identical with that found by Arago from the Puits de Crenelle 

 (Poggend. Ann. Bd xxxiv. S. 191). 



( 139 ) p. 165. Bo'issiiigauH, Sur la Profondeur a laquelle se trouve la 

 couche de Tempcnluro ii-variable entre les Tropiques, in the Auuales de 

 Chimie et de Physique, T. iii. 1833, p. 22524?. 



[The observations of Mr. Caldecott at Trevandrum in 1842 and 1843 

 (Quetelet, Climot de laBelgique, p. 137, et seq.) have shown that the stratum 

 of invariable temperature is not always found within the tropics at so small a 

 depth. At Trevandrum, at the depth of six French feet, the mean temperature 

 of different months, instead of being constant, varies as much as 3 6' Fah. ; 

 and the curve of annual ttmperature at that depth exhibits in very marked 

 characters two maxima corresponding to the double passage of the sun over 

 the zenith of Ticvandmm. EDITOR.] 



( 14 ) p. 166 Laplace, Exp. du Syst. du Monde, p. 229 and 263; Meca- 

 Dique celeste, T. v. p. 18 and 72. It should be remarked, that the fraction 

 Troth of a centesimal degree of the mercurial thermometer, given in the text 

 as the limit of the permanency of the temperature of the globe since the days of 

 Hipparchus, rests on the supposition that the dilatation from heat of the sub- 

 stances of which the E;irth is composed is equal to that of glass, or Tcrrnroo^ 

 for 1 C. Respecting this hypothesis, see Arago, Annuaire pour 1834, 

 p. 177190. 



( 141 ) p. 167. William Gilbert, of Colchester, whom Galileo entitled "great 

 to a degree which might be envied," said, " Magnus magnes ipse est globui 



