762 Transactions of the Society. 



depressions of a rounded form, corresponding severally to the points 

 of contact of the spherules. Mr. Eainey had already shown the 

 great probability — I might perhaps indeed say the certainty — 

 that the exquisite spherules which he had produced by his ex- 

 perimental method were built up first by the agglomeration of 

 small granules into small spherules, next by the agglomeration 

 of small spherules into larger spherules. 



More minutely considered, the actual process appeared to be not 

 a simple one of agglomeration of granules into spherules, and of 

 smaller spherules into larger spherules ; but, throughout, of re- 

 adjustment of the molecules constituting the several contingent 

 spherules. In the process of deposit, the first-formed spherules 

 were surrounded by others till groups were formed, comprehending 

 several spherules in contact with each other. Presently, their con- 

 stituent molecules, hitherto held in each independent sphere around 

 its centre by virtue of their mutual attraction, were disturbed by 

 the attraction of surrounding spheres, and were impelled to arrange 

 themselves round a new centre of mutual attraction placed some- 

 where in the midst of the group of spheres. In the end the small 

 spheres and granules vanished, having been incorporated into one 

 large sphere. 



Touching the erosion of the glass surface, Mr. Eainey argued 

 that when such a spherule was formed on a glass surface with the 

 surrounding colloid gum sticking to the glass surface, and actually 

 entering also into the composition of the sphere, the same attractive 

 power which had determined the incorporation into one sphere of a 

 number of spherules in contact with one another would determine 

 also the incorporation of adjoining molecules of the glass into the 

 incumbent sphere. The result would be the excavation of a pit 

 in the glass opposite each sphere in contact therewith. 



With these things already in my mind, on reading Surgeon- 

 Major Bidie's letter I wrote to him to suggest that the etching of 

 glass which he had observed, might be explained on the hypothesis 

 that " white-ant mud " consisted of a mixture of some colloid with 

 earthy matter. Dr. Bidie wrote to me afterwards a very courteous 

 letter telling me that, to his great regret, he could not provide me 

 with white-ant mud, but that he had sent some of the earth in 

 which the white ants worked. This I duly received. I made 

 only two experiments with the earth, which were inconclusive, and 

 I regret to be obliged to confess that the misplaced zeal of a house- 

 maid put an end to my opportunities of making further experi- 

 ments. 



It was, however, open to me to institute experiments bearing 

 upon the erosion of glass by carbonate and phosphate of lime 

 in the presence of colloids. So far, I have only used the carbonate. 

 The following experiments were set in action. In the first, strong 



