142 Scientific Intelligence. 
IV. (7) The beat-notes cannot be explained by reason of the 
difference-notes and summation-notes, because the number of their 
vibrations is in many cases different from what this cause might 
produce. 
(8) The audibility of the beats depends solely upon their num- 
ber and upon the intensity of the primary notes, and is independ- 
ent of the distance of the interval. 
g 
en the vibrations of a note vary periodically in intens- 
ity, the periodical maxima of vibration change into one note, if 
their number is sufficient. 
(14) The beat-note which is formed by two primary notes must 
always be weaker than the latter, although single beats are 
Giana than the notes which form them.— Phil. Mag., |, 417, 
: E. Oe 
Il. GkoLogy AND MINERALOGY. 
with fuller illustrations, and adds planations of his theory of 
: dds e 
the origin of mountains. The discussion should be read by all 
sions. His discussions are not free from misunderstandings of 
eological facts, and if they fail to be finally received it will 
or this reason. The subject is too large a one for a full state 
ment, in a book-notice, of the apparent difficulties and sources of 
doubt which might occur to an advocate of the latter theory. 
principal points in his theory of mountain-making as explained in 
the later part of his ements . : 
Accepting the proposition that there is a plastic condition of 
pata beneath the earth’s crust and that metamorphism is a “ hydro- - 
ermal process,” and believing that “the penetration of water to 
