342 i'HILOSOPHICAt. TRANSACTIONS. [aNNO 173^. 



bone left, weighed as much as the whole quantity of bone did at first. Now 

 the air had been confined in that bone, together with many sulphureous par- 

 ticles, in such a manner, that the mutual attraction of the sulphur and the air 

 had alternately destroyed each other's repulsive force, and brought those sub- 

 stances into a little compass ; but the fire in the distillation separated them 

 from each other, so as to restore them in a great measure, to their usual elas- 

 ticity. This appeared by bringing a candle near the mouth of the bottle that 

 held this revived air ; for every time the candle was brought near, the air took 

 fire, and flashed out of the bottle with a sulphureous smell. 



The air may be consolidated in many hard bodies, so as to be there quite 

 void of elasticity, and there do the office of a cement, till by the action of fire, 

 or some particular fermentations, it is again restored to its perfectly elastic state. 

 This is the meaning of Dr. Hales's words, when he says, that some bodies ab- 

 sorb, and others generate air ; and the same bodies do sometimes absorb, and 

 at other times generate air. He found more or less air in almost every solid 

 substance that he tried ; but, what was most remarkable, he found that the 

 calculus humanus, or stone taken out of a man's bladder, was made up of above 

 half its weight of air. 



Some have endeavoured to solve elasticity by attraction only ; as for example 

 — If the string a b, fig. 7, pU 7, be considered as made up of particles lying 

 over one another in the manner represented at a d b ; it is plain, that if the 

 point D be forcibly brought to c, the parts will be drawn from each other ; and 

 when the force, that stretched the string, ceases to act, the attraction of co- 

 hesion, which was hindered before, will take place, and bring back the string 

 to its former length and situation, after several vibrations. Now, though this 

 seems to agree pretty well with the phaenomena of a string in motion, it will by 

 no means solve the elasticity of a spring fastened at one end, and bent either 

 way at the other, like a knife or sword-blade, as in fig. 8. For if such a spring 

 be bent from A to a, the particles on the side c, which now becomes convex, 

 will be farther asunder at f, while the particles at d, carried to the concave 

 part E, will come closer together : so that the attraction, instead of making 

 the spring restore itself, will keep it in the situation in which it is, as it hap- 

 pens in bodies that have no elasticity, where perhaps only attraction obtains. 

 Thus a plate of lead, a plate of copper, and a plate of soft iron, stands bent. 



But the most probable way of accounting for the elasticity of springs, is to 

 consider both a repulsive and an attractive property in the particles, after the 

 manner of the black sand, which is attracted by the load-stone, and has been 

 shown, by Musctienbroek, to be nothing else but a great number of small 

 loadstones. 



