398 Intelligence and Miscellaneous Articles. 



These experiments can be varied without end. It is certainly 

 interesting to see the mutual effect of two or more vibrating 

 systems, each ruled more or less by the motions of its own super- 

 posed magnet, to witness the deformations and decompositions of 

 one molecular arrangement by the vibrations of a neighbouring 

 group, to note the changes in form which take place when a larger 

 magnet enters the combination, and to see the deformation of: 

 groups produced by the side action of a magnet placed near the 

 bowl. 



In the vertical lantern these exhibitions are suggestive of much 

 thought to the student. Of course they are merely suggestions 

 and illustrations of molecular actions and forms ; for they exhibit 

 only the results of actions in a plane ; so the student should be 

 careful how he draws conclusious from them as to the grouping 

 and mutual actions of molecules in space. 



I will here add that I use needles floating vertically and hori- 

 zontally in water as delicate and mobile indicators of magnetic 

 actions — such as the determination of the position of the poles in 

 magnets, and the displacement of the lines of magnetic force 

 during inductive action on plates of metal, at rest and in motion. 



The vibratory motions in the lines of force in the Bell telephone 

 have been studied from the motions of a needle (floating ver- 

 tically under the pole of the magnet) caused by moving to and fro 

 through determined distances the thin iron plate in front of this 

 magnet. These experiments are worth repeating by those who 

 desire clearer conceptions of the manner of action of that remark- 

 able instrument. — Silliman's American Journal, April 1878. 



ON SENSATIONS OF LIGHT AND OF COLOUR; IN DIRECT AND 

 INDIRECT VISION. BY E. LANDOLT AND A. CHARPENTIER. 



It is known that the fibres of the optic nerve expand at the back 

 part of the eye, forming by their terminations a nervous membrane 

 of hemispherical form which is termed the retina. It is upon this 

 that the images of external objects are depicted as in a camera 

 obscura ; and, undergoing certain modifications under the influence 

 of those images, it is the starting-point of the luminous sensations. 

 Now the eye utilizes for direct vision scarcely any of these images 

 but those formed upon the central part of the retina, named the 

 fovea centralis, and corresponding to the fixation-point ; the rest 

 are perceived more or less vaguely. There is therefore reason for 

 distinguishing between direct and indirect vision — the first, much 

 more distinct, corresponding to the objects at which we look, and 

 the second to the other objects in the visual field. 



Does this very clear difference between direct and indirect vision 

 depend on a real difference of sensibility in the different parts of 

 the retina ? This question we proposed to ourselves to determine, 

 having been prepared for the determination by the numerous series 

 of investigations already made by one of us upon the subject*. 

 * See Landolt, Ophthalmometrologie, 1874. 



