temperature of the interior of the earth. 1 1 5 



" 1 . Setting aside some of them, as being too uncertain and inac- 

 curate to be reasoned from, all the others announce, in a greater 

 or less degree, a notable increase of temperature on descending 

 from the surface of the earth towards the interior : this conclu- 

 sion may reasonably be allowed. 



" 2. The results collected at the Observatory of Paris, are 

 the only ones which enable us with something like certainty, to 

 express the law of this increase of temperature, viz. one degree 

 of the centigrade thermometer for twenty-eight metres in depth. 

 (That is, 1,8 of Fahr. for about ninety-two feet.) Hence in the 

 locality of Paris, water will boil at the depth of two thousand 

 five hundred and three metres, (about eight thousand two hun- 

 dred and twelve feet English.) 



" 3. Very few of the other results furnish numerical expres- 

 sions sufficiently approximative of the required law, to be of 

 use. These expressions vary from fifty-seven to thirteen me- 

 tres for one degree (cent.) of increased heat. The mean of 

 them announces an increase more rapid than has usually been 

 admitted. The concurrence of this testimony to the general 

 fact, is of weight, inasmuch as they comprise the result of 

 several series of local observations. 



" 4. In grouping by countries, the results admissible on what- 

 ever title ; I incline to think," says Cordier, ••' that the results 

 collected at the same place, depend upon, and are connected 

 with, not merely the imperfection of the experiments made, but 

 a real irregularity in the distribution of subterranean heat from 

 one country to another. 



" The observations hitherto published, possess therefore a real 

 value, efficient and incontestable. But others are still wanting : 

 and I proceed to give an account of those that I have made 

 myself. 



" J^ew and direct experiments on subterranean temperature^ (by 

 M. Cordier.) I preferred coal mines : because the branching 

 excavations are carried to a considerable distance from the shaft : 

 because from the ease of working them, the excavations ad- 

 vance rapidly, and are not so liable to be affected by external 

 circumstances : because it is easy to make speedily and with 

 great ease, deep holes in these mines : in which the tempera- 

 ture can be ascertained free from opposing circumstances. The 

 bulbs of the thermometers in these experiments were enveloped 

 in seven folds of silk paper ; so, however, as to admit the de- 

 gree on the scale to be easily come at. They were kept in a 

 tin case. They were so constructed, that being immersed in 

 melting ice, they took but twelve minutes to descend from 15^ 

 cent, to 0°, plunged 5 decimetres in a mass of moistened sand, in 

 a cellar they took twenty minutes to arrive at the temperature 

 of the cellar, losing eight degrees of their initial temperature. 



