188 Miscellanies. 



exists in the eye, in the posterior capsule of the lens ; and thus the 

 third image is accounted for. 



M. Sanson, a distinguished French surgeon, has taken advantage 

 of the above facts, to distinguish cataract from amaurosis, and has 

 been enabled to determine by this means some cases of supposed 

 amaurosis to be in fact cataract, and has treated them successfully by 

 operation. 



Dr. Mackenzie, an eminent ophthalmologist of Glasgow, has also 

 employed this means to determine the condition of the eye in glau- 

 coma. Dr. Hays remarked that he had resorted to the catoptric 

 examination of the eye in many cases, and believed that it would 

 prove as valuable a means of diagnosis in some of the diseases of the 

 eye, as auscultation is in those of the chest. 



Dr. Hays exhibited and explained several models, designed and con- 

 structed by Dr. John Neill, resident surgeon at Wills' Hospital, for the 

 purpose of illustrating the catoptric phenomena just explained. 



Dr. Patterson communicated verbally a method of using thin sheets 

 of lead by the blind in writing, reading, and musical notation, invented 

 by Mr. Joseph Saxton. The sheets of lead are three thousandths of 

 an inch in thickness. Dr. Patterson presented specimens of the wri- 

 ting and musical notation. 



Dr. Bache communicated the decease of Mr. George Pollok, a 

 member of the Society, who died in April last. 



May 17, 1839. — Dr. Hare made the following verbal communica- 

 tion relative to the blasting of rocks by the aid of galvanic ignition 

 in firing the chariie. 



The Doctor called the attention of the Society to the fact, that he 

 had, so long ago as the summer of 1831, demonstrated the safety, 

 certainty, and facility, which would arise in rock-blasting, whether 

 under water or otherwise, from a resort to galvanic apparatus as the 

 means of igniting the gunpowder employed. His efibrts had been 

 incited originally by those of a person named Shaw, who had pro- 

 cured a patent for employing mechanical electricity for the purpose ; 

 but who, finding that method of operating too precarious to be useful, 

 had applied to Dr. Hare to acquire a knowledge of more eflectual 

 means. This led to the experiments of which the result has been 

 published, both in the newspapers, and in the Journal of the Frank- 

 lin Institute. The subject was now referred to, in consequence of 

 the recent publication of analogous experiments by his friend. Prof, 

 Daniell, of King's College, London, who, in the case in point, no 

 doubt as in that in which he had " reinvented" Dr. Hare's concentric 

 blowpipe, was ignorant of the results previously obtained in this coun- 

 try. Prof. Daniell had, in blasting, used the highly ingenious appa- 



