28 Mr. R. Phillips on the Colours of a Jet of Steam 



the disintegrated surface, and become a permanent portion of the 

 solid crystaL 



In repeating and varying these experiments, I observed a 

 number of curious facts, which it would be out of place here to 

 describe. I immersed ciystals of alum in saturated solutions of 

 nitre and other salts, and observed many remarkable changes 

 upon the figures which they produced. The changes take place 

 principally upon the central parts of the figure, as shown in 

 fig. 33, which represents one of the forms which a solution of 

 nitre gave to the figure produced by alum ; but in other cases 

 the whole figure suffers a change. A ciystal of sulphate of 

 potash, which gave the hcxangular radiations already described, 

 produced the same figure, with twice the angular magnitude, 

 when dipped for a few seconds in a saturated solution of nitre. 



In consequence of having observed that the natural cleavage 

 planes of crystals gave indications of regular optical figures, 

 similar to those produced by solution, I was led to make some 

 experiments on the effects of mechanical abrasion, as produced 

 by coarse sandstone*, or by the action of a rasp or large-toothed 

 file. Surfaces thus torn up produced, in a rude manner, the 

 optical figure given by solution ; but what was very remarkable, 

 the figure had a different position, or had the position which solu- 

 tion would have developed on the opposite face. This is also true 

 of the figures produced by natural cleavage planes, in which the 

 separating surfaces have been slightly torn up. 



It is scarcely necessary to observe, that the power of producing 

 the optical figures described in this paper may be communicated 

 to wax or isinglass, &c. The impressions on isinglass enable us 

 to see the figure by transmitted light, and to observe its form 

 and dimensions with greater accuracy. 



AUerly, February 1, 183/. 



VII. On the Colours of a Jet of Steam and of the Atmosphere, 

 By Reuben Phillips, Esq, 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



I WAS not aware of the existence of the papers referred to 

 by M. Clausius until I saw his letter in the last Number of 

 the Magazine. Not having access to the foreign Journals, I am 

 unable to compare, or perhaps to correct, the following by what 

 M. Clausius has written. 



'%' 



* In fig. 12 the triangle ahc is brought out by grinding on a coarse hone 

 an octohedral surface of fluor-spar similarly situated to one on the natural 

 face. 



