OF ARTS AND SCIENCES. 71 



Mystic Pond, as at present constituted, consists of a thick stratum 

 of nearly pure water, resting on an undisturbed mass of saline water, 

 closely resembling that of the ocean. 



Professor Cooke exliibited some octohedral crystals deposit- 

 ed on a furnace product, which he had obtained accidentally 

 while experimenting on the compound of zinc and arsenic. The 

 crystals were so brilliant that their angles could be measured 

 with great precision, and they gave the exact angle of a regu- 

 lar octohedron. The composition of the crystals as shown by 

 analysis was, zinc 81.18, arsenic 18.82. Professor Cooke argued 

 that the arsenic in the crystals was present mainly in the con- 

 dition of impurity, and stated his reason for this opinion. He 

 considered therefore the crystals as showing that zinc might 

 crystallize in forms of the monometric system. 



He also exhibited a counterfeit American gold coin, of a 

 specious character, the gold abstracted from the interior being 

 ingeniously replaced by platinum. 



Professor Horsford gave additional details upon spontaneous 

 combustion, and mentioned a case in which iron-turnings sat- 

 urated with oil had been known to ignite. 



Dr. Beck, calling attention to the fragment of Petronius 

 discovered by him, and communicated by him to the Academy 

 about a year ago (now published in the eighth volume of the 

 Memoirs), read the following extract from a letter received 

 from Prof. Hertz of Greifswalde. 



" The ineditum which you have sent me has been these fourteen 

 years lying in my portfolio. I found it in a codex of the Marciana, 

 and copied it, but delayed publication. I am glad that you have, 

 in part, given it more complete than my codex presents it. It is 

 mentioned, however, earlier than the edition of Anthon, for which 

 you may find the proofs, which I have not at hand in this little 

 watering-place in the Baltic, in Goldast's Sylloge Adnotationum in 

 Petronium. In many things, this Petronius agrees with Isidorus in 

 his Origines, which, in my opinion, he has used ; its importance for 

 Gellius is, as I think, subordinate. It was my original intention to 

 publish the piece with the readings of the Venetian MS. in the Ehein 



