756 Transactions of tee American Institute. 



Prof. John Phin stated that microscope lenses may be cleansed by 

 washing them with weak hydrofluoric acid. 



Dr. D. D. Parmelee stated that a common method of etching is by 

 printing the pattern with printer's ink on soft paper, transferring it 

 to the glass, and etching the spaces with hydrofluoric acid. 



Mr. "W. E. Partridge — This is done by a stencil plate. 



Dr. Parmelee regarded the use of the stencil plate less convenient 

 than printing; since the stencil plate necessarily leaves many places 

 which must afterward be connected by an expert engraver. 



Mr. W. E. Partridge regarded the stencil-plate process as cheaper 

 in consequence of the fact that an etched glass pattern seldom requires 

 to be duplicated. 



Mr. Stade, not being present, further discussion was postponed 

 until he should appear to explain his process. 



The President read the following items of scientific news : 



I. Silica, in All its Varieties, Diamagnetic. 



Prof. Dove has successfully suspended, between the poles of a 

 powerful electro-magnet, sections cut from colorless rock-crystal, smoky 

 quartz, agates composed of alternating layers, chalcedony, jasper, 

 amethyst, and other varieties of quartz. Their uniform behavior in 

 the magnetic field shows that all the different kinds of native silica are 

 diamagnetic. 



II. Pyro-electricity of Crystals. 

 Herr W. Hansel has examined over sixty varieties of topaz, par- 

 ticularly in reference to their pyro-electric properties, and has been 

 led to the conclusion that pyro-electricity is unnecessarily correlated 

 with hemimorphism, but is a general property of all crystals. In 

 hemimorphic crystals the opposite extremities of the principal axis, 

 being dissimilar, assume opposite polar conditions ; while in crystals 

 having the two ends physically similar, the same polar condition is 

 found at each extremity. In hemimorphic crystals the distribution of 

 electricity seems to depend on the asymmetry of the molecules, and 

 is therefore not altered by an external change of form ; while in those 

 crystals which are not hemimorphic, the distribution of electricity 

 depends in a great degree on external form and arrangement, and may, 

 therefore, be modified by a change of shape. 



III. Selenitic Mortar. 

 Col. Scott, of South Kensington, England, has invented a mortar 

 for which several advantages are claimed. It is made by simply mix- 



