Correspondence—Mr. A. R. Hunt. 287 
near Craveggia in North Piedmont. Crystallographically it is very 
similar to rutile and tapiolite with axial ratio a: ¢ = 0°6456. Some 
of the crystals are elongated along the pyramid edge and are probably 
twins similar to those of ilmenorutile. ‘The mineral is black and 
opaque, and has a specific gravity of 5°59. It contains titanic acid, 
zirconia, oxide of iron, and niobic and tantalic acid. The result of 
analyses suggests the formula 3 FeO (Ta Nb,) O;, 4 ZrO,, 9 TiO,, 
which may be written as a mixture of the three molecules Fe 
(Ta Nbg) O;, Fe ZrO, O;, and Ti'Ti, O, in the proportion of 1: 2: 3. 
Chemically it is very similar to ilmenorutile, but contains about 
28 per cent. of Zr O3, replacing part of the Ti Oy. 
CORRESPONDENCE. 
PROFESSOR C. D. WALCOTT, LL.D., For. Mem. Grou. Soc. 
Str, — At the annnal meeting of the Board of Regents of the 
Smithsonian Institution, held on January 28rd, 1907, Charles 
Doolittle Walcott, LL.D., was duly elected Secretary of the 
Smithsonian Institution, to succeed the late Samuel Pierpont Langley. 
MetvittE W. Focter; 
Chancellor of the Smithsonian Institution. 
SMITHSONIAN INsTITUTION, WASHINGTON. 
MRS. AYRTON’S THEORY OF RIPPLE-MARK. 
Srr,—I am grateful to Mrs. Ayrton for having replied to my note 
of despair in the Magazine for February last. Our sole object is the 
truth in a question of small account with physicists, but of great 
importance to geologists. Owing to the action of the Royal Society 
and of the British Association in having Mrs. Ayrton’s new theory 
presented to the scientific public in a demonstration at a conversazione, 
in a lecture to a section, and in a very short abstract in the Proc. Roy. 
Soc., there is next to nothing on public record, as even Mrs. Ayrton’ s 
abstract of her British Association lecture was not published in the 
Report, so there is little to discuss. 
In her letter Mrs. Ayrton writes: ‘I actually showed at the lecture 
a series of periodically oscillating waves moving in one direction over 
a fixed bottom, and expending themselves on a sandy shore, and 
proved that under such waves ripples formed exactly as they did 
an the moving tank with vertical sides.”’ 
Mrs. Ayrton’s own description of this experiment is as follows :— 
*‘T can imitate exactly the sand ripples on the sea-shore with water 
running in one direction only, if I slope the sand so that the water 
runs up it, as it does on the sea-shore, and if by means of a paddle 
I send a series of waves along the water in the direction in which it 
is running, if, in fact, I imitate the incoming tide.” (Abstract, p. 3. 
Italics are mine throughout. ) 
It is most important to note that, as stated, the ripples thus made 
are like those made on the shore, but they are dissimilar from those 
