14 SIR DAVID BREWSTEK ON THE EXISTENCE OF CRYSTALS 



analogous kind ; but as it appeared unexpectedly, and was instantly followed by 

 the explosion of the crystal, I could neither observe it accurately, nor confirm 

 what I did observe, by a repetition of the experiment. I have, therefore, some 

 satisfaction in describing a similar phenomenon, seen frequently, and under more 

 favourable circumstances, not only from its intrinsic interest, but because a dis- 

 tino-uishcd philosopher had treated with an air of incredibility an observation 

 which I had made of a similar kind. There can be no higher testimony to the 

 novelty and importance of a scientific fact, than when a competent judge raises 

 it to the supernatural. 



I come now to dcscriloe a property of the dense fluid, so new and remarkable 

 that it cannot fail to excite the attention of chemists. This fluid occupies the 

 whole of a large cavity ABCD E, Fig. 10, with tlie exception of a bubble at A, 

 which must be either a vacuum, as it is in all cavities containing only this fluid, 

 or a bubble of the expansible fluid, or the vapour of the dense fluid, or some gase- 

 ous body. It cannot be a vacunm ; because it expands with heat, in place of being 

 filled up by the expansion of the fluid. It cannot be the expansible fluid ; because 

 cold would contract it, and produce a vacuity. It cannot be the vapour of the 

 expansible fluid ; because there is no expansible fluid to throw it olf, and it has 

 not the optical properties of its vapour. It cannot be the vapour of the fluid 

 in the cavity ; for it does not disappear by the application of cold, and does not 

 become a vacuity, Avhich fills up by the expansion of the fluid. It is, therefore, 

 an independent gas, which exhibits the following phenomena. 



When heat is applied, the bubble A expands, not by the degradation of its 

 circidar margin passhig into A^apour, as in the vapour cavities described in a former 

 paper, but by the rapid enlargement of its area. When it attains a certain size, 

 it throws off" a secondary bubl)le B, which passes over a sort of ridge or weir m n o, 

 in the bottom of the cavitj', and settles at B. If the heat is continued, these two 

 bubbles increase in size ; but it was instantl.y withdrawn when B had begun to 

 swell. As the topaz began to cool, both the bubbles A and B quickly contracted. 

 The primary bubble A returned gradually to its original condition, and B, when 

 reduced to a single speck, Avould have disappeared, liad the cooling not been stop- 

 ped. Tliis speck swelled again by the application of heat, and so did the bubble A. 

 When the speck at B was allowed to vanish, which it did on the spot which the 

 bubble occupied, the fresh application of heat did not revive it at that spot, but 

 merely expanded the primary bubble A, which again threw off" a secondary 

 bubble B, Avhich exhibited by heat and cold the same phenomena as before. These 

 experiments I repeated many times with the snme result. It will naturally be 

 asked, what was the condition of the fluid itself which has the property of expanding 

 by heat ; and Avhat became of it while a part of the space which it occupied was 

 appropriated by the bubble B, and the addition to the bubble A ? An accidental 

 circumstance enables me to answer this question, Avbich would have been 



