Miscellanies. 187 



Specimens of the salt were exhibited, together with the apparatus 

 employed in the qualitative examination of the compound, the consti- 

 tution of which was made manifest by proper chemical re-agents. 



The following candidates were elected members of the Society : 



Humphrey Lloyd, A. M., of Trinity College, Dublin. 



J. K. Paulding, Secretary of the Navy of the United States. 



John Ludlow, D. D., Provost of the University of Pennsylvania 



Benjamin "W. Richards, of Philadelphia. 



George W. Bethune, D. D., of Philadelphia. 



George M. Justice, of Philadelphia. 



May 3, 1839. — Prof. Bache called the attention of the Society to 

 the donation of transparent models of crystals, presented to the cabi- 

 net by Prof. Alexander. 



He stated that these models had all the advantages of those made 

 from glass, with greater convenience in the construction of them. 

 The thin plates of mica are readily marked with a sharp instrument, 

 and easily cut. The parts are put together with diamond cement, it 

 having been found that this is a much better method of connecting 

 the pieces composing the model, than by cutting the sheets partly 

 through and using the mica as a hinge, which renders the sheets lia- 

 ble to split. The forms resulting from the cleavage of crystals, &c. 

 may be represented in these models as in those of glass. 



Dr. Hays made a verbal communication relative to the catoptric 

 examination of the eye, as a means of distinguishing the morbid con- 

 ditions of the transparent tissues of that organ. 



He stated that when a lighted candle is held before an eye, the 

 pupil of which is dilated, and in which there is no obscurity of the 

 transparent tissues, three distinct images of the flame are visible ; two 

 upright and one inverted, the latter appearing between the two former. 



Experiments made to determine the causes of these reflected ima- 

 ges, and the changes which occur in their number, position, &c. have 

 shown that if a light be placed before the convex face of a single 

 watch glass, or of several of them superimposed, one or more up- 

 right images of the flame will be seen, according to the number of 

 glasses employed.* Now in the eye there are two superimposed 

 convex surfaces, viz. — 1st, the cornea ; and 2d, the anterior capsule 

 of the crystalline lens. Thus the formation of the two upright ima- 

 ges is explained. Again, if a light be placed before the concave sur- 

 face of a watch glass, an inverted image is seen. Such a surface 



* To be strictly accurate, it should be said that each of these images is double, 

 for one is reflected from each surface of the glass, and these images are the more 

 distinctly double, the thicker the glass. 



