Royal Society. 497 



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 through 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 

 different 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.U.S., Astronomer 

 lloyal, 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. All 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 tlie bow. Observations were also 

 made for determining the horizontal intensity at each of the stations. 

 Tlie deviations of dipping needles at three of these stations were 

 also determined, when the plane of vil)ration coincided with that of 

 the ship's keel, and also when at right angles to it. 



After describing the particular method of observing rendered ne- 

 cessarj' 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. Tiie most 

 striking features in these results are, the very great apjiareut change 

 in the direction of tlie ship's head, as indicated hy the compass nearest 

 the stern, corresponding to a small real change in one jjarticular 

 position, the former change being 97", whereas the latter was only 

 Pldl. Mmj. S. 3. Vol. 14. No. 92. iiuppl. July, 1839. '-' K 



