4 Improvements in Physical Science (Jan. 
opague screen. Avago has observed that a piece of glass plate of a 
certain thickness may be substituted for the opaque screen with a 
similar effect. If the glass be very thin, the bands do not disap- 
pear, but are displaced from their former situation. This displace- 
ment increases with the thickness of the glass, till at last the bands 
disappear entirely. (Ibid. %. 199.) 
3. Diffraction.—There is an important paper on this subject by 
M. Fresnel in the Ann. de Chim. et Phys. i. 239, in which he gives 
an account of a curious set of observations, and gives a theory of 
diffraction founded on the hypothesis that light is owing to the un- 
dulations of a subtile fluid. It is not possible here to give an idea 
of his reasoning without entering into details which would be in- 
compatible with the limited extent of this sketch; but the paper 
deserves the attention of all those who are interested in the science 
of optics. 
IV. STATICS. 
1. Upon this subject the most important set of experiments pub- 
lished during the course of the year is to be found in Col. Beaufoy’s 
paper on the Stability of Vessels, published in the Annals of Philo- 
sophy, vii. 184, This paper is of such a nature as to preclude the 
possibility of giving an abstract of it. I must, therefore, rest satis- 
fied with referring the reader tothe paper itself. ‘These experiments 
agree with the doctrine laid down by Mr. Richard Hall Gower in 
his Observations on the present Construction of Ships, a book 
printed in 1807 ; but as almost the whole impression was consumed 
by the burning of Mr. Bensley’s house, Bolt-court, Fleet-street, on 
Nov. 5, 1807, it has probably fallen into the hands of a very small 
number of readers. — 
2. I may here also mention Col. Beaufoy’s important paper on the 
Resistance of Air, and on Air as a moving Power, printed in the 
Annals of Philosophy, viii. 94, though it belongs rather to pneu- 
matics than statics. It is also incapable of abridgment, but deserves 
the particular attention both of philosophers and practical engineers, 
3. To Col. Beaufoy we are indebted, likewise, for an ingenious 
contrivance for determining an invariable standard of measure by 
the distance which a ball falls in a given time. His description is 
so concise that I must here also refer the reader to the original paper 
in the Annals of Philosophy, viii. 211. 
V. ELECTRICITY. 
1. Zamloni’s Column.—A great number of papers have been 
published on this new electrical instrument; but no new fact of any 
importance has been brought to light. Dr. Schubler, of Hofwyl, 
has shown that it has no connection with the electrical state of the 
atmosphere (Schweigger’s Journal, xv. 111, 126 ; xvi. 111). Hein- 
rich found, as had been already observed by others, that the motion 
of the pendulum varies considerably in its velocity. On Nov. 10, 
