Prof. Norton on Molecular Physics. 205 



stress on the suggestion, that if there are reasons for asserting 

 that the problem of the greatest solid of revolution ought to have 

 a continuous solution, there will also be reasons for making a 

 similar assertion for the problem respecting the course of a ship. 



I will advert to one fact which, although not essential, will be 

 of use in studying what has been written on the problem under 

 discussion. 



I have quoted above the ordinary formula 



Bu= (*A(Sy— 2?Sa?)^a? + B 



as that which will probably be most familiar to readers of the 

 Magazine. It has, however, been shown by some of the most 

 eminent writers on the subject, that we may use the formula 



Bu = § ASy dec + B ; 



A is the same in the two formulae, but B is not. I retain the 

 opinion that I have elsewhere expressed in favour of the second 

 formula: it seems to me to be obtained in a more simple and 

 intelligible manner than the first, and to be better adapted to the 

 higher investigations by which we discriminate between a maxi- 

 mum and a minimum. 



Although I do not admit that the articles in the Magazine for 

 March and for July have contributed directly to the solution of 

 the problem discussed, yet I am glad that attention has been 

 again drawn to the subject. My own conviction is that the pro- 

 blem is no longer perplexing, but that its true solution is that 

 which was stated and supported in the Magazine for June. 



Cambridge, August 2, 1866. 



XXVI. On Molecular Physics, By Prof. W. A. Norton*. 

 [Continued from vol. xxxi. p. 282.] 

 TX/FAGNETIC Condition of the Sun. — The intimate magnetic 

 relation subsisting between the earth and sun enforce, 

 even in the present general exposition of terrestrial magnetism, 

 a brief consideration of the probable magnetic condition of the 

 sun. We have seen that the sun's surface must be traversed by 

 magnetic currents developed in two ways, — (1) by reason of the 

 sun's rotation about an axis ; (2) by reason of the combined 

 effect of its motion of rotation and its motion of translation through 

 space (vol. xxxi. p. 280). According to the most reliable determi- 

 nations the sun's progressive motion is directed toward a point 

 whose longitude is 253° 16', and north latitude 57° 27', and with 

 a velocity of 4| miles per second, while his velocity of rotation at 

 the equator is I '3 mile per second. Accordingly the currents 

 developed from the second cause must originate at the parts of 

 * From Silliman's Journal for March 1866. 



