318 



The third section of the paper is occupied with these theoretical 

 considerations, and in this Prof. Henry shows, that if the fact be 

 granted, that the deflection of the needle is due to the whole amount 

 of induced electricity, whatever may be its intensity, all the pheno- 

 mena may be explained by the different degrees of rapidity with 

 which a given amount of inductive action is expended. 



When the development or the diminution of the quantity of a gal- 

 vanic current is sufficiently rapid, a shock is produced; but if the 

 same amount of development is produced more slowly, no shock per- 

 haps will be obtained, although the deflection of the needle will be as 

 great as before. The neutralizing effects of the interposed plate, in 

 reference to the shock and not to the needle, are direct consequences 

 of these principles, and most of the perplexing phenomena, described 

 in Prof. Henry's last papers are referred to the same cause. 



Prof. Henry illustrates his views by the artifice of a curve, the ab- 

 scisses of which represent the time of the increase or diminution of 

 the quantity of a current, and the ordinates the amount of inductive 

 force produced by the same. 



The Committee, consisting of Mr. Nuttall, Mr. Lea, and Dr. 

 Coates, to whom was referred a communication by Miss Mar- 

 garetta H. Morris, on the Cecidomyia Destructor or Hessian 

 Fly, reported in favour of publication, which was ordered ac- 

 cordingly. 



The Committee express the opinion, that should the observations of 

 Miss Morris be ultimately proved correct, they will eventuate in con- 

 siderable benefit to the agricultural community, and, through it, to the 

 public. Miss Morris believes she has established, that the ovum of 

 this destructive insect is deposited by the parent in the seed of the 

 wheat, and not, as previously supposed, in the stalk or culm. She 

 has watched the progress of the animal since June, 1836, and has 

 satisfied herself that she has frequently seen the larva within the seed. 

 She has also detected the larva, at various stages of its progress, 

 from the seed to between the body of the stalk and the sheath of the 

 leaves. In the latter situation it passes into the pupa or " flaxseed 

 state." According to the observations of Miss Morris, the recently 

 hatched larva penetrates to the centre of the straw, where it may be 

 found of a pale greenish-white semi-transparent appearance, in form 

 somewhat resembling a silk-worm. From one to six of these have 



