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ANNUAL OF SCIENTIFIC DISCOVERY. 



the friction, was equal to the compressing force ; then noting the weight 

 which allowed the piston to return exactly to its first position : this, 

 together with the friction, is equal to the compressing force ; but, as these 

 two compressing forces are equal, the friction is equal to half the differ- 

 ence of the two weights used, and is then a matter of very simple calcula- 

 tion. Mr. Hopkins then gave the results of the experiments, of which the 

 following are the most important : 



Of course, when the weight was on the piston, the substance was 

 under atmospheric presstire, or about 15 Ib. to the square inch ; and the 

 pressure of 7,790 Ib. per square inch was just that at which the Britannia 

 Bridge had been raised. Mr. Hopkins had also tried the metallic alloys 

 which fuse at low temperatures, but had not detected any elevation of 

 fusing temperature required by increasing the pressure ; but these experi- 

 ments required to be repeated and confirmed before they could be relied 

 upon. 



A paper was also read in this connection by Mr. Fairbairn, " On the 

 Solidification of Bodies under Great Pressure," which contained the 

 results of a portion of the experiments conducted by himself, Mr. Hop- 

 kins and Mr. Joule, at the request of the Association, and by means of 

 funds supplied for that purpose by the Royal Society. At the last meeting 

 at Hull, Mr. Hopkins alluded to these experiments, and then explained the 

 nature of the apparatus invented by Mr. Fairbairn for submitting the 

 substances to be operated on to the enormous pressure of 90,000 Ib. on the 

 square inch. In these inquiries the objects kept in view were, to ascertain 

 the exact laws which govern the cohesive strength of bodies in their pres- 

 ent physical condition, and how far a knowledge of those laws may con- 

 duce to the reduction of the metals, and their subsequent solidification 

 under circumstances whereby increased strength and density may be 

 obtained. The experiments commenced with spermaceti, bars of which 

 were cast and left to solidify at the same temperature, but under different 

 pressures. When pressure was applied to these bars, the one that sus- 

 tained a pressure of 40.793 Ib. carried 7.52 Ib. per square inch more weight 

 than one submitted to a pressure of 6,421 Ib., the ratio being in favor of 

 the more strongly compressed bar, in its power of resistance to a tensile 

 strain, as 1 to .876. It appeared from these experiments that bodies when 

 - solidified under pressure have not only their densities greatly increased, 

 but their molecular structure is also materially affected, so as to increase 



