676 PHILOSOPHICAL TRANSACTIONS. [aNNO 174g. 



The first natural philosophers who endeavoured to investigate the cause of 

 these phenomena, imagined that they found it in the air. Some of them sup- 

 posed, that this air was shut up in the drop by the crust which the cold water 

 forms on its surface while it is yet red-hot; and attributed its rupture to the vio- 

 lence with which this air issued through the too narrow passage made for it, in 

 breaking the small end of the drop. Others maintained, on the contrary, that 

 the drop, in this state, contained no air at all, nor any thing but particles of fire, 

 or subtile matter; in short a mere vacuum as to air; and that the sudden bursting 

 of the drop was occasioned by the impetuous entry of the air into this kind of 

 vacuum. In fine, the Cartesians have substituted their subtile matter in the 

 room of this exterior air, and say, that the drop is bursten by tne less subtile 

 particles of this matter; which entering with force into the drop by the opening 

 made in it, and finding large pores on the inside, and small ones on the outside, 

 burst the sides of the drop, by rushing from the centre to the circumference, 

 with which its passage is obstructed. 



Messrs. Mariotte and Homberg came afterwards: being provided with an air 

 pump, they caused one of these drops to be broken in vacuo; and Homberg 

 having observed, that it there broke better, and with a louder report, than in 

 the open air; they both inferred, that neither the impetuous entry of the out- 

 ward air, nor that of a fluid somewhat less gross, could be the cause of this 

 shock ; because the receiver of the air-pump is void of these fluids ; and even if 

 a little should remain there, it is too much rarefied, and too thin to be capable 

 of such an effect. 



Mr. Mariotte, through some remains of attachment to an opinion, which he 

 had held till that time, did not entirely exclude the exterior air from the cause of 

 the phenomena of the drop; but thought proper to add another to it; which he 

 makes use of as a substitute in cases like those of the preceding experiment, 

 where the insufficiency of the air, or of a fluid nearly similar to it, plainly 

 appears. 



Mr. Homberg shows no indulgence to the exterior fluid; and ascribes the 

 whole to the new cause, which is, the quality of tempered glass, which the drop 

 acquires, like steel, by being thrown red-hot into cold water. This tempering," 

 according to these great academicians, confers at the same time more springiness 

 to the parts, and less connection with each other. When a steel sword-blade is 

 bent forcibly, it breaks more easily than one of iron; and the jarring which is 

 occasioned by its spring, is capable of breaking the other parts of the blade; 

 and thus we see, that it generally breaks into several pieces. This blade is the 

 image of the glass drop. 



This is the point to which Mons. le Cat found things brought, when he began 

 to study the phenomena of the glas^ drop. The air was partly banished from the 



