PLATES. 



I. II. Illustrative of Mr. R. T. Forster's Paper on the Molecular Con- 

 stitution of Crystals. 

 III. IV. "V. Illustrative of Prof. Tyndall's Paper on the Nature of the 

 Force by which Bodies are repelled from the Poles of a Magnet. 



ERRATUM. 



Page 50, line 6, /or Peter William B.\rlow read William Henry 

 Barlow. 



