140 Mr. W. N. Hartley on Attraction and [Apr. 12, 



sections were cut, there was a multitude of cavities, many of considerable 

 size. They all contained one liquid, water, and what appeared to be a 

 gas-bubble, which was attracted by heat. A slice of the crystal was 

 mounted between pieces of stout sheet platinum, and so placed on the 

 stage of the microscope that it could be easily taken off and replaced at 

 once in exactly the same position, so that the cavity under observation 

 would be within the focus of the object-glass. By immersing the specimen 

 in hot mercury, and instantly after removal examining it with the micro- 

 scope, I ascertained that at 150° C. the liquid had just expanded so as to 

 entirely fill the space. It is evident, then, that little or no gas is present. 



It was next necessary to ascertain the lowest temperature of a body 

 by which the bubble could be attracted. This was accomplished in a most 

 satisfactory manner by selecting a cavity which was plainly visible with 

 a 2-inch objective. A loug test-tube, having a diameter of § of an inch, 

 was filled with water, immersed in which was a fine thermometer. The 

 tube was heated, and experiments were repeatedly made while it was 

 cooling to find out when it ceased to attract the bubble. 



A number of trials showed that at 76° C. attraction was powerful, at 

 71° C. it was somewhat feeble, but below this temperature there was no 

 action sufficient to overcome gravitation. Further experiments were 

 made in a straight tube-like cavity, which from its size and its regularity 

 of shape was exceptionally good for the purpose. It measured x j^qq of 

 an inch, and the bubble was °f an i ncn * n diameter. It moved about 

 on change of position as freely as the bubble in a spirit-level. Proceed- 

 ing as before, the temperature of the crystal being 16° C. and that of 

 the tube 21° C, the bubble could be attracted in a horizontal direction 

 only ; but when the tube was warmed to 60° C. its power of attraction 

 was sufficient to overcome the buoyancy of the bubble, and draw it down- 

 wards to the extremity of the cavity. 



A piece of rock-crystal was examined which contained both water and 

 carbonic-acid cavities in juxtaposition. These water-bubbles were very 

 easily attracted, as will be seen by the following experiments. A cavity was 

 chosen with a bubble moving as easily as the bubble in a spirit-level ; its 

 size was x jfo of an inch, and the diameter of the bubble j^o~u of 

 an inch. 



"While the section of the crystal was maintained at 16° C. a platinum 

 wire was heated in mercury and applied to the cavity, showing the fol- 

 lowing effects :— ■ 



Temperature of wire. Effect produced. 



25 Feeble attraction. 



27 The same. 



29 Strong attraction. 



31 Very strong attraction. 



65 Just sufficiently strong to overcome gravitation. ' 



71 . Attracted strongly in opposition to gravitation. 



