Mr. J. J. Hood on the Laws of Chemical Change. 371 



had to this circumstance, formula (E) obtains a higher nu- 

 merical value than (F). From this it follows that the vertical 

 component of the induction-force at the astronomic pole is less 

 than at the point for which formula (E) holds good. If in 

 formula (C) we make /=90 + 34, we obtain the sought force 

 for a point t' situated at 56° latitude counted from d. For- 

 mula (C) is in this way transformed into the following : — 



JcM(r sin 34° + p sin 17°> sin 51° 



(r*+pZ-~2rp cos 51°)! 



M.(r sin 34°-? sin 17°)p sin 51° Q) 



Formula (Gr) having a higher numerical value than (E), the 

 point at which the vertical component of the induction-force 

 will be the same as at the point t must be at a higher latitude 

 than t r . From this it follows that the aforesaid annular zone 

 will cut the plane in question at a point t" situated between 

 the astronomic pole and t' . Thus the zone presenting the 

 greatest frequency of aurorse boreales must be at a higher lati- 

 tude in Europe and Asia than in North America. 

 [To be continued.] 



XL IX. On the Laics of Chemical Change. — Part I. 

 By John J. Hood, Esq.* 



WHILE studying chemistry under Prof. Mills, I was 

 much struck by the want of knowledge concerning 

 the laws regulating the amount of change which chemically 

 active bodies undergo in a given time, and in what manner 

 the rate of change is influenced by heat, electricity, &c. Many 

 cases of change have been investigated and represented gra- 

 phically ; but, as far as I am aware, no theory has been 

 given confirmed by experiment whereby, the temperature and 

 amount of active bodies undergoing change being known, 

 the amount of remaining energy at any time can be calcu- 

 lated. The nearest approach to such a theory was given by 

 Messrs. Harcourt and Esson in the - Phil. Trans.' for 1867, 

 where they showed that for the case of hydric peroxide re- 

 acting on hydric iodide, 



H 2 2 + 2HI = 2H 2 + I 2 , 



the amount of change was proportional to the amount of 

 acting substance, considering hydric peroxide as the active 

 body. 



* Communicated "by the Author. 



2B2 



