on
Sound,' 3rd edition, p. 227.] f, at some distance beyond the other
end. When the reed sounded, the flame in front of it was violently
agitated, and roared boisterously. Turning on the gas, and lighting
it as it issued from the slits, the air above the flames became so
heterogeneous that the sensitive flame was instantly stilled, rising
from a height of 6 inches to a height of 18 inches. Here we had the
acoustic opacity of the air in front of the South Foreland strikingly
imitated. [Footnote: Lectures on Sound, 3rd ed, p. 268.] Turning off
the gas, and removing the sensitive flame to f, some distance behind
the reed, it burned there tranquilly, though the reed was sounding.
Again lighting the gas as it issued from the brass tubes, the sound
reflected from the heterogeneous air threw the sensitive flame into
violent agitation. Here we had imitated the aerial echoes heard when
standing behind the syren-trumpet at the South Foreland. The
experiment is extremely simple, and in the highest degree impressive.

Fig. 11.

*****

The explosive rapidity of dynamite marks it as a substance specially
suitable for the production of sound. At the suggestion of Professor
Dewar, Mr. McRoberts has carried out a series of experiments on
dynamite, with extremely promising results. Immediately after the
delivery of the foregoing lecture I was informed that Mr. Brock
proposed the employment of dynamite in the Collinson rocket.

********************

XI. ON THE STUDY OF PHYSICS.

[Footnote: From a lecture delivered in the Royal Institution of Great
Britain in the Spring of 1854.]

I HOLD in my hand an uncorrected proof of the syllabus of this course
of lectures, and the title of the present lecture A there stated to be
'On the Importance of the Study of Physics as a Means of Education.'
The corrected proof, however, contains the title: 'On the Importance
of the Study of Physics as a Branch of Education.' Small as this
editorial alteration may seem, the two words suggest two radically
distinct modes of viewing the subject before us. The term Education
is sometimes applied to a single faculty or organ, and if we know
wherein the education of a single faculty consists, this will help us
to clearer notions regarding the education of the sum of all the
faculties, or of the mind. When, for example, we speak of the
education of the voice, what do we mean? There are certain membranes
at the top of the windpipe whic