444- Royal Society. 



cargo. The author shows that the deviation of the compass arising 

 from the attraction of the vessel, was exactly of the kind which was 

 likely to occasion this great mistake in the ship's reckoning: for 

 the distance run by the Thetis being about eighty miles, if the 

 local attraction of the vessel had been equal to that of the Glou- 

 cester, she would have passed five miles nearer to Cape Frio than 

 her reckoning, an error quite sufficient to account for the fatal ca- 

 tastrophe. r lhe author hence infers the importance of bestowing 

 more attention than has hitherto been given to the influence of the 

 local attraction of vessels, and to the application of the proper 

 means of correction. 



April 28. A paper was read, " On the Anatomy and Physiology 

 of the Minute and Capillary Vessels." By Marshall Hall, M.D. 



The author, considering the minute blood-vessels as arteries or 

 veins, as long as their subdivisions or junctions are attended with a 

 change in their dimensions, denominates them capillaries when no 

 such change occurs. With the aid of an achromatic microscope of 

 Dollond's, he endeavoured to ascertain what differences existed be- 

 tween the systemic and pulmonary circulations, as far as regards 

 these vessels. Dr. Edwards had observed that the batrachian rep- 

 tiles are speedily killed by immersion in hot water : and the author 

 found that although by plunging any of the animals of that order 

 into water at 120 of Fahrenheit they are speedily deprived of all 

 power of sensation and of motion, yet the action of the heart con- 

 tinues for a very long time, thus affording an opportunity of leisurely 

 observing the phaenomena of the circulation, without the infliction 

 of pain, and without any disturbance from the struggles of the 

 animal. 



In the fins and tail of the stickleback, the number of the capillary 

 vessels is small, and their distribution simple : the artery runs along 

 the border of each ray till it reaches the extremity, when it is re- 

 flected, and becoming a vein, pursues a retrograde course by the 

 side of the artery. This simplicity in the mode of its distribution 

 corresponds with the simple nature of the function of the part, 

 which is merely an instrument for swimming. In the web of the 

 frog's foot, which is adapted to a greater variety of mechanical 

 purposes, the system of blood-vessels is somewhat more complex ; 

 the capillaries are more abundant ; the arteries, which are nearly 

 equal in number to the veins, pursue a more direct course ; and 

 the veins are larger and more tortuous. No pulsatory movement 

 can be perceived in the blood while moving in the capillaries or 

 veins, as long as the circulation is unimpeded and in the natural 

 state. The author was unable to detect any anastomoses between 

 the minute arteries, although they are frequent among the veins, 

 where they give rise to occasional oscillations in the currents of 

 blood flowing through them : neither could he discover any instance, 

 in the web of the frog, of the immediate termination of an artery in 

 a vein. The velocity of the blood is retarded immediately in its 

 passage from the arteries into the capillaries, because the united 

 capacity of the branches is greater than that of the trunk which 

 divides to form them. In the mesentery of the toad, the distribu- 

 tion 



