by Rock-crushing and its Consequences. 7 



temperature nearly approaching the softening point of cast iron*; 

 so that a large range of rigidity must exist for the exaltation ot 

 its temperature in the way above suggested ; and in the state 

 of aggregation which we are warranted in supposing rocky 

 masses to exist at considerable depths, it is probable that this 

 range of rigidity would be even further extended than in the 

 case of granites found at or near the present surface of our globe. 



There is a close analogy between the conditions of gradual 

 exaltation of temperature above sketched, and those by which 

 aerolites, flying at an immense velocity through our atmosphere, 

 are heated from the temperature of the stellar spaces to that of 

 incandescence or even fusion of those bodies. The aerolite, 

 which, according to Schiaparelli, may in some instances be forced 

 through our atmosphere with a relative velocity exceeding 3500 

 feet per second (one enormously exceeding that at which air can 

 rush into a vacuum), compresses the stratum of air immediately 

 in advance in almost the same manner as if at the .first instant of 

 contact the air were a rigid body. The temperature developed is 

 greater as the velocity of compression is so, and as the volume 

 compressed is less ; the most highly heated air is therefore the 

 stratum directly in contact at any instant with the stone ; and 

 the latter licks up more or less of the heat as it passes through a 

 succession of such compressed strata, and so receives continual 

 accessions of heat until the temperature of the meteoric stone 

 itself reaches the limit given by that of the stratum of compressed 

 air in immediate contact with it at any instant. If a body as 

 mobile and compressible as air can thus by sufficiently rapid 

 compression be raised above the temperature of incandescence, 

 we may readily conceive how great an exaltation of temperature 

 may be produced in the rigid materials of our earth's crust when 

 exposed to a pressure which in ay be viewed as limitless in refer- 

 ence to the resistance opposed to it, and which, in consequence 

 of the conditions of elastic resilience hereafter referred to, may 

 give rise to motion and crushing with velocities even exceeding 

 those with which aerolites traverse our atmosphere. 



The well-known experiment of cutting a hard steel file in two 

 by the rapid rotation of a thin disk of soft sheet iron pressed 

 against it is another example. The heat developed at the work- 

 ing-point, so far as it is communicated to the disk, is rapidly 



* The observations upon which these statements are founded have been 

 made after various great conflagrations of stores or warehouses at London, 

 Liverpool, and Dublin, into the construction of which granite blocks and 

 cast iron in columns, girders, &c. largely entered. The cast iron was 

 either melted or softened to the consistence of soap ; the granite heated to 

 like temperature, except being split in various directions, was found un- 

 altered, except more or less in colour, after having been again cooled. 



