Mr Sang on the Construction of Circular Towers. 245 



nally caused it to be dug. This venerable old Hindoo, Chin- 

 nana Gouda, whose hair and beard are blanched by age, paid 

 me a visit at the mine. He informed me that it is upwards of 

 forty years ago since he dug it ; and that„ until Mr Heath's 

 discovery, about twenty-two years ago, he had not the slightest 

 idea of the treasures contained in his own well, and of which 

 he had been robbed for eighteen years by the people he em- 

 ployed. 



In India, the beryl appears to be almost confined to this par- 

 ticular district. The natives, however, inform me that it oc- 

 curs at Vaniambadi, at the northern base of the Nilgherries, in 

 rocks of a similar age and petrographical character. In Europe 

 it occurs also in the primitive rocks — in the granite and gneiss 

 formations. 



On the Construction of Circular Towers. By Edward Sang, 

 Esq., Civil-Engineer, Edinburgh, M. S. A. Communicated 

 by the Society of Arts.* 



Some years ago I submitted to the Society of Arts an essay 

 on the construction of Oblique Arches, in which the complete 

 theory of cylindroid arches was developed, and the applica- 

 tion of that general theory to some particular cases was given. 

 From that inquiry, there resulted several beautiful general 

 propositions concerning the voussoirs of which arches are to 

 be built; in particular, it was found that in a properly con- 

 structed arch, where the bed of the stone is proportioned to 

 the strain which it has to bear, the cross sections of the arch 

 stones are all equivalent to each other. 



The investigation of the oblique arch is only one case of 

 the general theory of Vaults ; and I would have devoted this 

 paper to that general theory, had I not felt that an abstract 

 generality is best appreciated after a few of its special cases 

 have been examined. In the present paper it is, therefore^ 

 proposed to examine another practically important case of 

 vault, namely, that which occurs in building a circular signal 

 tower. 



* Reatl before the Society of Arts for Scotland 15th April 1840. 



