20 DR BREWSTKR on the Existence of Two AVw Fluids 



heat. This perplexing fact induced me to examine the cavity 

 under the circumstances of total reflexion, and it was then ap- 

 parent, that N was neither a vacuity nor a space filled with gas, 

 but a portion of the new fluid floating as it were on the second 

 fluid WW. 



This phenomenon was analogous to what takes place in 

 the right hand portion of the cavity in Fig. 11.; but, as there 

 were here no vacuities into which the expansion of the new 

 fluid could push the second fluid, the difficulty remained un- 

 solved. 



It may be proper to mention, that the cavities which present 

 this phenomenon are most frequently connected by a dark line 

 with other cavities, accompanied with vacuities, as shewn at N, 

 in Fig. 16, and 17. In Fig. 16., by a considerable cold, I have 

 caused a small vacuity to appear at V ; but it sometimes remains, 

 and sometimes disappears. 



As there are cavities, however, such as that in Fig. 14., where 

 no connection can be traced with other cavities, and where the 

 fluid N seems to expand, and WW to contract, it is necessary to 

 seek for some explanation of this singular anomaly. That the 

 expansions and contractions are here only apparent, cannot, we 

 think, be doubted. Let AB, therefore, Plate II. Fig. 18. be a 

 section of the cavity in Fig. 14., where the new fluid NN floats 

 as it were on the other. When NN is heated, the effect of the 

 heat will tend to diminish the cohesive force of the fluid WW, 

 and to make the fluid WW spread itself into a thinner film, as 

 shewn in Fig. 19., so that it seems to occupy a greater space, as 

 shewn in Fig. 15. 



In support of this explanation, I may adduce the case of other 

 cavities in topaz, such as those shewn in Figs. 20. and 21., where 

 the globule N of the new fluid never expands with heat, an 

 effect which is probably owing to its occupying the whole thick- 



