210 [March, 1845. 



matter, cohere to an extent far beyond what the mere external 

 pressure of the air would be adequate to produce. 



Besides the tendency of similar materials to cohere when 

 brought into close contiguity, the two bars had the farther advan- 

 tage of developing in each other avery highdegree of magnetism. 

 This, their vertical position alone, without motion, being so near 

 the direction of the magnetic dip, would certainly in time pro- 

 duce ; and with the revolving motion, which (as every machinist 

 knows from the operations of boring and drilling) produces a high 

 magnetic state, it would occur with much greater promptitude and 

 intensity. 



It was represented that the juncture had not apparently been 

 heated, at least not discoloured. This latter fact is perfectly con- 

 sistent, however, withsuch adegree of temperature as would allow 

 much mobility of particles, and greatly aid the high pressure of 

 more than a ton weight per square inch, and a strong magnetic 

 attraction to bring the revolving surfaces into the sphere of actual 

 cohesion. The grease box with which the two bars are stated to 

 have been surrounded would defend the surfaces from oxidation, 

 the cause of discolouring, and would interpose no effectual pre- 

 ventive against the contact of two plain surfaces, revolving in the 

 circumstances now supposed. 



Professor Johnson referred to his own experiments, made many 

 years ago, in which it was found that bars of ironbroken at atem- 

 perature of 5 or 600 degrees, and in the magnetic meridian, be- 

 came strongly and permanently magnetic. He referred to the 

 proceedings of the Academy (vol. 1, page 144,) for an account of 

 the phenomena then observed. 



It is a subject of regret that the proprietors of the mill in ques- 

 tion, had not preserved the united bars, to be submitted to compe- 

 tent persons for a minute examination of their condition and pro- 

 perties. 



Prof. Henry D. Rogers stated that the specimen of Oolite 

 rock presented by him this evening, had been obtained from 

 Dr. Binney of Boston. It had been found in Florida, in a 

 somewhat extensive deposit, by a correspondent of that gen- 

 tleman. Though identical in colour and structure with the 



