PHILOSOPHICAL SOCIETY OF WASHINGTON. 39 



The minutes of the last meeting were read and adopted. 



Dr. J. R, M. Ieby, of the Johns Hopkins University, upon 

 invitation of the General Committee of the Society, read a com- 

 munication entitled 



SOME OBSERVATIONS ON THE CRYSTALLINE STATE OF MATTER. 



He first discussed the nature of crystals and their distinctions 

 from the other states of matter, and remarked that the crystal is 

 the most perfect expression of the molecular forces of matter 

 with which we are acquainted, since it is the state of matter in 

 which the equilibrium of those forces is least disturbed by heat 

 motion. 



In the second part of the paper Haiiy's theory of the constitu- 

 tion of crystals was discussed, its importance insisted upon, and 

 its reconsideration in connection with all the phenomena of crys- 

 tals was urged. 



In the third part of the paper the theory of Haiiy was applied 

 to the mineral species calcite. In the case of this luineral — one 

 of the most Protean in its crystalline forms — the author thought 

 the results so fully in accordance with the theory that much Avas 

 to be hoped from its careful application to other crystals. 



Dr. Irby also adverted to the experiment of Harting, who 

 produced forms similar to those of the coccoliths obtained from 

 the ocean depths by treating the albumen of eggs with solutions 

 of lime. 



Remarks upon the paper were made by Messrs. Antisell and 

 Newcomb, 



The second communication was by Mr. Harkness, upon 



THE COLOR CORRECTIONS OF ACHROMATIC OBJECTIVES. 

 (abstkact.) 



1st. From any three pieces of glass suitable for making a cor- 

 rected objective, but not fulfilling the conditions necessary for the 

 complete destruction of the secondary spectrum, it will always 

 be possible to select two pieces from which a double objective 

 can be made that will be superior to any triple objective made 

 from all three of the pieces. 



2d. The color correction of an objective is completely defined 

 by stating the wave-length of the light for which it gives the 

 minimum focal distance. 



