1877.] Repulsion of Bubbles by Heat. 139 



with a ball-syringe on to the object, and then directing it on to the bulb 

 of a delicate thermometer. With the most sensitive bubbles three or four 

 degrees Centigrade were found to be amply sufficient. 



The letters in italics {a, b, c) witkin the drawings of fluid-cavities indicate the posi- 

 tions of the gaseous carbonic acid, liquid carbonic acid, and water respectively. 

 Fig. 1. Cavity in a topaz, x 35 diameters. 

 Fig. 2. Cavity in rock-crystal. X 46 diameters. 

 Fig. 3. Cavity in tourmaline. 



Fig. 4. Cavity in rock-crystal, containing a bubble repelled by heat. X 250 diameters. 



Fig. 5. Six cavities in rock-crystal adjacent to each other. The bubbles in A and A' 

 are repelled by heat ; in B, C, and D they are attracted. These cavities con- 

 tain water. E contains liquid carbonic acid only, x 250 diameters. 



Fig. 6. Two cavities in rock-crystal, The bubbles contain liquid carbonic acid floating 

 on water. These bubbles are repelled or attracted by a source of heat 

 according to the temperature of the specimen. 



Fig. 7. A and B are cavities in felstone, containing liquid carbonic acid and a vibrating 

 bubble. C, D, and E are diagrams representing the motion of the bubbles 

 under different conditions of temperature. 



The following experiments show the conditions under which such 

 attraction takes place. In a specimen of rock-crystal from which several 



