Mr. D. Vaughau on the Solar Spots. 859 



other having the same centre G, the same mass m, and the same 

 arm of inertia A. For not only at its two extremities^ but at 

 every other point of its direction,— considered as an inflexible 

 hne,— such a rod would be capable of striking an obstacle with 

 the same force Q as the body itself at its corresponding point. 



It is true that this rod, by moving with the same angular ve- 

 locity in an opposite direction to the body, would not, on encoun- 

 tering the latter, be able to ]n-oduce equilibrium and destroy all 

 the body's motion ; nevertheless, it would reduce to a state of 

 rest all points along its own direction, so that the body would be 

 able to preserve only a motion of rotation around this line. But 

 a body which rotates around a line is incapable of producing any 

 percussion at any point of that line ; hence, if we regard merely 

 the percussion which the body is capable of producing at any 

 pomt of the line DD', this percussion is exactly the same as that 

 of the rod ; it is in this sense only that, at the moment of the 

 shock, the rod may be substituted for the body*. 



Note. Mr. Hayward of University College, Durham, has kindly 

 drawn my attention to the following oversight : 



At the end of the second paragraph of art. 21, Chap. I., instead 

 of the words. " but this is always less than the impulse P," read 

 '• but this is greater than, equal to, or less than the impulse P accord- 

 ing as K^ is greater than, equal to, or less than Sa^." A correction 

 of a similar kind is also necessary at the end of the last paragraph 

 of art. 22, Chap. II.— T. A. H. f a f 



XLV. On the Solar Spots and the Variable Stars. 

 By Daniel VAuoHANf. 



TF the chemical pheenomena of the heavens can be traced to de- 

 J- terminate causes, we may confidently hope for a considerable 

 extension of our knowledge respecting the fixed stars. It seems 

 unreasonable to regard the development of light on these distant 

 orbs, as dependent on operations wholly different from any which 

 we are permitted to examine on our own globe. A careful study 

 of the subject for many years has led me to conclude, that the 

 space-pervading medium is the essential element of suns. As this 

 fluid attains an adequate density by their powerful attraction, it 

 undergoes a continual chemical action above their surfaces, and 

 serves to dispense floods of heat and light to surrounding worlds. 

 la the brief exposition of my views, which was sent to the last 



* M. Poiiisot has announced, but has not yet pubhshed, the continua- 

 tion of Ills memoir. 



t Communicated by the Autiior. 



