340 On the Forms and States of Fluids [1831 . 



sunshine, and the light reflected from its surface received on a 

 screen, it formed a very beautiful and regular image ; but the 

 screen required to be placed very near to the metal, because 

 of the short focal lengths of the depressions on the mercurial 

 surface. 



79. It is sometimes difficult to arrive by inspection at a 

 satisfactory conclusion of the forms and arrangements thus 

 presented, because of multiplied reflexion and the particular 

 condition of the whole, which will be described hereafter (95). 

 When observed, well formed with vibrations so slow as to pro- 

 duce three or four elevations in a linear inch (70), they are seen 

 to be conoidal heaps rounded above, and apparently passing 

 into each other below by a curvature in the opposite direction. 

 When arranged regularly, each is surrounded by eight others ; 

 so that, a single light being used, nine images may be sent from 

 each elevation to the eye. These are still further complicated, 

 when transparent fluids are used, by reflexions from the glass 

 beneath. The use of ink (75) removes a good deal of the diffi- 

 culty experienced, and the production of slow, regular, sus- 

 tained vibrations, more (67. 69). 



80. These elevations I will endeavour to distinguish hence- 

 forth by the term heaps. 



81. The crispation on the long plate of glass described (67) 

 always ultimately assumed a rectangular arrangement, i. e. the 

 heaps were equidistant, and in rows parallel or at right angles 

 to each other. The rows usually form angles of 45 to the 

 sides of the plate at the commencement ; but if the vibration 

 be continued, the whole system usually wheels round through 

 45 until the rows coincide with the edges of the plate. 



82. The lateral dimension of the heaps remained constant, 

 notwithstanding considerable variations in the force of vibra- 

 tion. But it was soon found that variation in the depth of 

 water affected their number ; that with less water the heaps 

 were smaller, and with more water larger, though the sound 

 therefore and the number of vibrations in a given period re- 

 mained the same. The number of heaps could be reduced to 

 eight or increased to eleven and a half in the three inches by a 

 change in no other condition than the depth of fluid. 



83. With the above plate (67. 8 1 ) the appearances were usually 

 in the following order, the pool of water being, quadrangular or 



