Page:Popular Science Monthly Volume 6.djvu/467

Rh considerably, which fact showed an increase in the resistance of the air.

MM. Planavergne claim the priority of the theoretic idea which I have enunciated, and show, in fact, that they had published, some years since, a memoir, in which this theory is explicitly stated. However, these authors have furnished no experimental demonstrations of their views; consequently, it has appeared to me that it would be interesting to continue the researches which I had begun, and to determine, as accurately as possible, on one hand, the phases and variable conditions of the resistance of the air to a moving body which displaces it with a uniform motion; on the other hand, to find the increase of the resistance of the air under the wings of an apparatus which is transported with determinate velocities.

.—Determination, of the variable and constant resistances opposed by the air to a moving body which displaces the air with a uniform motion.

In a solid framework, which glides easily on an horizontal plane, I placed a light screen, with its plane vertical and perpendicular to the direction of its motion. This screen turns around an horizontal axis; and an arm attached to it is charged with an additional weight until perfect equilibrium is established between the arm and the screen itself. This having been done, we have no fear of the inertia of one or another part of the system causing the screen to revolve around its axis at the beginning of its motion of translation. If such a movement of rotation does take place, we must attribute it to the resistance offered by the air.

Behind the screen is placed a little manometric apparatus, which communicates, by means of a tube, with a drum, having a lever resting on its membrane.



The apparatus having been thus arranged, we give to it a uniform motion of translation which lasts half or a quarter of a second, and we obtain on a revolving cylinder the above trace of the point of the writing-lever attached to the membrane of the recording drum.

When the screen is at rest, the apparatus traces an horizontal line