March, 1845.] 209 



Specimen of a true concretionary Oolite rock ; from the south 

 of Florida. From Prof. H. D. Rogers. 



A communication from Mr. Haldeman was read, dated 

 Chiquesalunga, March 3d, 1S45, suggesting to the Society an 

 exchange of publications with the "Swiss General Association 

 of Naturalists." 



A paper by Dr. Hallowell, entitled "Descriptions of Rep- 

 tiles from South America, supposed to be new;" and a 

 second paper, entitled " Descriptions of new species of African 

 Reptiles," were read and referred to the following committee, 

 viz. : Dr. Blanding, Rev. Mr. McFarland, and Dr. Hol- 

 brook. 



Professor Johnson made some remarks on a recent occurrence 

 of the adhesion and apparently perfect cementation of two steel 

 bars in the cold state, while revolving- in contact with each other. 

 The one, the upright shaft, bearing a heavy mill stone, and the 

 other a cylinder of the same diameter, also standing vertical, and 

 on the head of which the shaft was supported. Both bars were 

 of the same diameter, (rather more than an inch) and their ends 

 were planes running in contact. The muTbeing suddenly arrest- 

 ed and the two bars found strongly united, efforts to separate 

 them proved ineffectual, and the attempt led to a fracture out of 

 the original juncture. 



This occurrence was stated to be in accordance with observa- 

 vations already familiar to those who have studied the phenome- 

 na of cohesion, and particularly the habitudes of steel and iron, 

 when subjected to mechanical motions tending to modify the con- 

 dition of their ultimate molecules. 



The simple pressing together at ordinary temperatures of two 

 clean and plain surfaces of lead causes them to cohere with much 

 tenacity. Two or more portions of the same metal at an elevat- 

 ed temperature, issuing under pressure from a reservoir of semi- 

 fluid metal, may unite under simple pressure to form a continuous 

 tube, so perfect, that it will part at any other section as soon 

 as at the line of juncture. Two disks of glass, perfectly clean, 

 and placed in contact without the intervention of air or of organic 



