Prof. Snell on new articles of Philosophical Apparatus, 21 
Figures 1 and 2 present a view of the two instruments as they 
stand connected in the philosophical cabinet. They are, how- 
ever, entirely distinct, and the upper one may be removed from 
the lower, and either of them taken into the lecture room by 
itself. Fig. 2 exhibits the movements of sea waves. The box 
containing the mechanism is about two feet long, one foot wide 
and seven inches high. ‘The lower half of the front projects 
beyond the upper half, so as to leave a space one fourth of an 
inch wide, in which the iron pieces (a a) rise and fall. There are 
thirty pieces of sheet iron, marked (a a), three fourths of an inch 
wide and four inches high, standing as closely as possible without 
danger of contact. ‘They are painted black, to appear in strong 
contrast with the white front, which forms the ground behind 
them. ‘These represent columns of water, and by turning the 
crank are made to rise and fall in such order that the waves 
which they form advance regularly in one direction and pass off, 
while other waves form and succeed them perpetually. If an 
observer fixes his attention upon the form of the waves, he sees 
them roll along horizontally, like billows of the ocean; but the 
moment his attention is directed to a single column, he as plainly 
