34 PROCEEDINGS OF THE 



The deepest coal-mine in this district is the Monkwearmouth Colliery, which 

 reaches a depth of 1,800 feet below the surface of the ground, and nearly as much 

 below the level of the sea. The observed temperature of the strata at this depth 

 agrees pretty closely with what has been ascertained in other localities, and 

 shows that the increase takes place at the rate of 1' Fahr to about 60 feet of 

 depth. Assuming the temperature of subterranean fusion to be 3,000°, and that 

 the increase of heat at greater depths continues uniform (which, however, is by no 

 means certain), the thickness of the film which separates us from the fiery oceatt 

 beneath will be about 34 miles — a thickness which may be fairly represented by 

 the skin of a peach taken in relation to the body of the fruit which it covers. 

 The depth of 4,000 feet, which has been assumed as the limit at which coal could 

 be worked, would probably be attended by an increase of heat exceeding the 

 powers of human endurance. In the Monkwearmouth Colliery, which is less than 

 half that depth, the temperature of the air in the workings is about 84° Fahr. 

 which is considered to be nearly as high as is consistent with the great bodily 

 exertion necessary in the operation of mining. The computations, therefore, of 

 the duration of coal would probably require a considerable reduction m conse- 

 quence of too great a depth being assumed as practicable. 



In the course of the preceding observations I have had occasion to speak of the 

 Bun as the great source of motive power on our earth, and I must not omit to 

 refer to recent discoveries connected with that most glorious body. Of all the 

 results which science has produced withm the last few years, none has been more 

 unexpected than that by which we are enabled to test the materials of which the 

 8un is made, and prove their identity, in part at least, with those of our planet. 

 The spectrum experiments of Buusen and Kirchhoff have not only shown all this, 

 but they have also corroborated previous conjectures as to the luminous envelope 

 of the sun. I have still to advert to Mr. Nasmyth's remarkable discovery, that 

 the bright surface of the sun is composed of an aggregation of apparently solid 

 forms, shaped like willow-leaves or some well known forms of Diatomacese, and 

 interlacing one another in every direction. The forms are so regular in size and 

 shape, as to have led to a suggestion from one of our profoundest philosophers of 

 their being organisms, possibly even partaking of the nature of life, but at all 

 events closely connected with the heating and vivifying influences of the sun. 

 These mysterious objects, which, since Mr. Nasmyth discovered them, have been 

 seen by other observers as well, are computed to be each "not less than 1,000 

 miles in length and about 100 miles in breadth. The enormous chasms in the 

 Bun's photosphere, to which we apply the diminutive term " spots," exhibit the 

 extremities of these leaf-like bodies pointing inwards, and fringing the sides of 

 the cavern far down into the abyss. Sometimes they form a sort of rope or bridge 

 across the chasm, and appear to adhere to one another by lateral attraction. I 

 can imagine nothing more deserving of the scrutiny of observers than these 

 extraordinary forms. The sympathy, also, which appears to exist between forces 

 operating in the sun, and magnetic forces belonging to the earth merits a contin- 

 uance of that close attention which it has already received from the British 

 Association, and of labours such as General Sabine has with so much ability and 

 effect devoted to the elucidation of the subject. I may here notice that most 



