310 A liaises of Books . [A f in i . 



increased by diminishing the diameter, or by reefing the paddles, 

 the increase of speed being in the ratio of the square roots of the 

 radii, or the cube roots of the powers employed. This is important 

 in long voyages, where the immersion of the paddles is great, in 

 consequence of the quantity of coals with which steam vessels are 

 required to be laden. An increase of speed will be given, amounting 

 to nearly one mile per hour, by reducing the diameter of the wheel 

 so as to allow the engine to perform its full duty. 



7- An advantage would be gained by a wheel of large diameter, 

 as far as the immersion of the paddle produced by loading the vessel 

 is concerned, as it would not so sensibly affect the angle of inclination 

 at which it entered the water. But, to have large wheels, it is 

 necessary either to have the engines made with long strokes, or to 

 have the paddle-wheel on a different shaft, in order to diminish the 

 speed. 



Anatomy and Physiology. 

 Sir Charles Bell, in his paper on the brain, begins by enumerating 

 some of the impediments which have retarded the discovery of the 

 structure and functions of that organ. 1. The nature of the inquiry, 

 since opposite results must be expected in making investigation upon 

 a subject so delicate. In practice, we find effects produced by causes 

 which seem quite inadequate. The presence of a small specula of bone 

 will sometimes be attended by no consequence, and at other times will 

 give rise to violent convulsions. 2. The disturbance of its circulation, 

 for no organ depends more intimately upon the condition of the circu- 

 lation within it than the brain. 3. The most frequent source of 

 error is the obscurity which hangs over the subject, for not one of 

 the grand divisions of the brain has yet been distinguished by its 

 function. Hence have arisen imaginary theories which always tend 

 to bury a science in obscurity. The present inquiries of the author 

 are directed to the prosecution of the fact discovered by himself, that 

 the nerves of motion and sensation originate from different sources. 

 He follows up these tracts ; marks the portion of the brain to which 

 they ultimately tend ; ascertains the effect of diseases on these parts, 

 and compares the system with the anatomical details. The conse- 

 quences which he has drawn from this investigation are : 1st, that 

 sensibility and motion belong to the cerebrum : 2d, that two columns 

 descend from each hemisphere, one of which, the anterior, gives origin 

 to the anterior spiral roots of the spinal nerves, and is dedicated to 

 voluntary motion ; the other sends out the posterior roots of the 

 spinal nerves, and the sensitive root of the fifth nerve, and is the 

 column for sensation : 3d, that the columns of motion which come 

 from different sides of the cerebrum, join and decussate in the me- 

 dulla oblongata, and that the columns of sensation also join and 

 decussate in the medulla oblongata: 4th, that these anterior and 

 posterior columns bear, in every circumstance, a very close resem- 

 blance to one another, agreeing in their sensorial expansions, being 

 widely extended in. their hemispheres, and in every respect, except in 

 the nervous filaments to which they give origin. 



