211 



pound process, to distinguish it from the mere hammering of the wire 

 upon the rod, as practised by him formerly, and which he terms the 

 simple process. He then enters into extended details of his several 

 experiments, of which the following are the principal results : first, 

 that the compound process is more effectual in the production of mag- 

 netism than the simple one, though the ratio of augmentation does 

 not appear determinate. In one experiment, the maximum effect of 

 the simple process was an attractive force capable of lifting between 

 186 and 246 grains, while the compound process augmented the lift- 

 ing power to 326 grains. In another, the simple process gave a lift- 

 ing power of 246 grains, the compound of 345 grains. Moreover, 

 the efficacy of the compound process is much less manifest upon long 

 than short wires, and is greatly impaired by diminishing the size of 

 the rods. 



In respect to the influence of the temper of the wire upon the de- 

 gree of magnetism developed, Mr. Scoresby found that the softer the 

 wire the more susceptible it became of this magnetic condition. 



The author concludes this paper with some theoretical remarks re- 

 specting the influence of percussion in disposing the particles of iron 

 to acquire and retain magnetism, which he thinks may tend to ex- 

 plain some otherwise obscure phenomena; and which seem to render 

 it probable that the process of percussion may be applied, in con- 

 nexion with other modes of magnetizing, for giving increased power 

 to magnets. 



On Semi-decussation of the Optic Nerves. By William Hyde Wol- 

 laston, M.D. V.P.R.S. Read February 19, 1824. [Phil. Trans. 

 1824, p. 222.] 



In the human brain, the optic nerves, after passing forward to a 

 short distance from their origin in the thalami, become incorporated ; 

 and from the point of union two nerves are sent off, one to each eye. 

 To this united portion the term Decussation has been applied, under 

 the supposition that though the fibres do intermix, they still continue 

 onward in their original direction ; and that those from the right side 

 cross over wholly to supply the left eye, while the right eye is simi- 

 larly supplied by fibres from the left thalamus. Anatomists have 

 considered this opinion as confirmed, by the circumstance of the 

 nerves actually crossing each other as two perfectly distinct cords in 

 some fish ; the author, however, from a species of blindness under 

 which he has more than once suffered, concludes that a different dis- 

 tribution of the nerves takes place in the human subject. This pe- 

 culiar state of vision consisted in seeing only half of every object, 

 the loss of sight being in both eyes towards the left, and of short 

 duration only. In reflecting upon this subject, a certain arrange- 

 ment of the optic nerves, not consistent with the generally received 

 hypothesis of their decussation, occurred to him. Since the corre- 

 sponding points of the two eyes, he observes, sympathize in disease, 



r 2 



