Page:Proceedings of the Royal Society of London Vol 4.djvu/165

Rh facts and observations the arguments adduced in its support. He endeavours, from a review of the circumstances under which the veins are placed, to show the inconclusiveness of the objections which have been urged by various physiologists against his and the late Sir David Barry's theory of suction : namely, that the sides of a pliant vessel, when a force of suction is applied, will collapse and arrest the further transmission of fluid though that channel. The considerations which he deems adequate to give efficacy to the power of suction in the veins of a living animal are, first, the posi- tion of the veins by which, though pliant vessels, they acquire in some degree the properties of rigid tubes ; secondly, the immersion of the venous blood in a medium of a specific gravity at least equal to its own ; thirdly, the constant introduction of recrementitious matter into the venous system at its capillary extremities by which the volume of the venous blood is increased, and its motion urged onwards to the heart in distended vessels ; and lastly, the gravity of the fluid itself, creating an outward pressure at all parts of the veins below the highest level of the venous system. The author il- lustrates his positions by the different quantities of blood which are found to flow from the divided vessels of an ox, according to the difl'erent modes in which the animal is slaughtered.

The reading of a paper, entitled, " Account of Experiments on Iron-built Ships, instituted for the purpose of discovering a Correc- tion for the Deviation of the Compass produced by the Iron of the Ships." By George Biddell Airy, Esq., A.M., F.R.S., Astronomer Royal, was also resumed and concluded.

In this paper the problem of the deviation of a ship's compass, arising from the influence of the iron in the ship, more particularly in iron-built ships, is fully investigated ; and the principles on which the correction for this deviation depends having been determined, practical methods for neutralizing the deviating forces are deduced and illustrated by experimental application. The author states that, for the purpose of ascertaining the laws of the deviation of the com- pass in the iron-built steam-ship the Rainbow, four stations were selected in that vessel, about four feet above the deck, and at these the deviations of the horizontal compasses were determined in the various positions of the ship's head. xA.ll these stations were in the vertical plane, passing through the ship's keel, three being in the after part of the ship and one near the bow. Observations were also made for determining the horizontal intensity at each of the stations. The deviations of dipping needles at three of these stations were also determined, when the plane of vibration coincided with that of the ship's keel, and also when at right angles to it.

After describing the particular method of observing rendered necessary by the nature of the vessel and the circumstances of her position, the author gives the disturbance of the horizontal compass at the four stations deduced from the observations. The most striking features in these results are, the very great apparent change in the direction of the ship's head, as indicated by the compass nearest