2 Mr. J. Ball on the Cause of the Descent of Glaciers. 



terras, before a London audience, at the theatre of the Royal 

 Institution. 



The arguments of Canon Moseley have not passed unques- 

 tioned. In March 1869 Mr. James Croll published in these 

 pages a reply to Canon Moseley's paper shortly before commu- 

 nicated to the Royal Society, wherein, after admitting that the 

 argument directed against the " ordinary opinion " on the sub- 

 ject of glacier-motion must be considered "decisive," he attempted 

 to refute the general conclusion by ingenious considerations as 

 to the condition of the molecules of a mass of ice when acted on 

 by external heat. 



In the ' Alpine Journal ' for February last, Mr. William 

 Mathews, well known as a successful explorer of the Alps, and 

 familiar with the phenomena of glaciers, has given an able sum- 

 mary of the present state of our knowledge of the causes of 

 glacier- motion, along with a careful analysis of the views of 

 Canon Moseley as developed in his various writings. In the 

 same paper several weighty objections to Canon Moseley's views 

 are urged by Mr. Mathews ; and the result of an interesting ex- 

 periment made by the writer, in conjunction with Mr. A. P. 

 Osier, added a fact of considerable value to the materials avail- 

 able in the discussion. A further experiment, made by the 

 same observers under circumstances that much enhanced its im- 

 portance, was published by Mr. Mathews in the Number of 

 1 Nature ' for the 24th of March last. The latest contribution 

 to the discussion with which I am acquainted is a reply by Canon 

 Moseley to the strictures of Mr. Mathews, published in the 

 < Alpine Journal' for May 1870. 



I trust that I shall be acquitted of any want of respect for the 

 learned and ingenious author of what has been well termed the 

 "crawling theory" of glacier motion, if I discuss it very briefly, 

 and content myself with pointing out a few only of what appear 

 to me insurmountable objections to its acceptance. It was sug- 

 gested, as is well known, by the casual observation of the gradual 

 descent of sheet lead on a roof of moderate pitch. Although the 

 resistance of friction was far greater than the force of gravity 

 acting in the direction of descent, it was found that the lead con- 

 tinued to slide or crawl down the slope, and was even able to 

 draw out nails that had been driven through it into the rafters 

 beneath with a view to hold it fast. Mr. Moseley detected the 

 physical cause of the phenomenon. He showed that it was a 

 necessary consequence of alternations of temperature. When a 

 body lying upon an inclined plane expands under the influence 

 of heat, the expansion is mainly in the direction of least resist- 

 ance. When acting in the upward direction, the expansive force 

 has to overcome the resistance opposed by friction, and, in addi- 



