164 Intelligence and Miscellaneous Articles. 
changed when the eyes are on the same level and look through the 
transparent sides of the box containing the water*, After illus- 
trating in this manner the changing magnitude of the images, the 
objective foci may be made to pass into virtual ones, and the corre- 
sponding uninverted magnified images will make their appearance. 
The agreement between convex lenses of water surrounded by air, 
and concave lenses of air in water, may be followed further by distin- 
guishing the central and circumferential rays. So long as the foci 
remain objective, the circumferential rays intersect nearer to the 
lens than the central ones, but further from it when the foci are 
virtual. With the concave water-lens surrounded by air, and the 
convex air-lens in water, the foci are all virtual, and those of the cir- 
cumferential rays are always nearer to the lens than the foci of the 
central rays. 
Although all this is easily explained by the simple laws of refrac- 
tion, it was always instructive and surprising to spectators to observe 
how a mere change of medium converts a diverging lens into a burn- 
ing glass, and a microscope into a telescope. 
To complete the above experiments, the action of a concave lens 
may be destroyed by a convex one on placing one behind the other 
in the water; or if, instead of being all equal, the curvatures of the 
lenses be properly adjusted, a Galilean telescope or a Briicke’s mag- 
nifier may be constructed with a concave object-glass and a convex 
eyepiece. 
‘The consequences of the above phenomena of refraction, relative 
to the phenomena of reflexion which present themselves with water- 
lenses in air and air-lenses in water, also hold good. 
These hollow lenses, too, serve to compare with each other the 
several effects presented by differently refracting bodies, such as 
water and clove-oil, with the same form of lens in different media.— 
Poggendorff’s Annalen, vol. cvii. p. 323. 
ON THE FIXATION OF THE MAGNETIC IMAGE. BY M. J. NICKLES. 
The name of magnetic image is given to the appearance observed 
when iron filings are placed on a paper screen over the poles of a 
powerful magnet. It may be fixed in the following manner :—A 
sheet of waxed paper is placed over the poles of a powerful magnet, 
and kept in its position by means of a screen interposed between 
the paper and the poles. The image is then developed in the usual 
way; and when this is effected, a hot brick or crucible cover is 
brought near enough to melt the wax. The melted wax by capil- 
larity penetrates the agglomeration of filings, just as water penetrates 
amass of sand. It is necessary that the layer of wax have a con- 
siderable thickness, in order to be sufficient for the action of capil- 
larity. On cooling, the wax retains the filings in their place, and 
they present the same appearance as if still under the influence of 
the magnet.—Comptes Rendus, Nov. 27, 1859. 
* This box is 1 metre long, 170 millims. high, and 110 millims. broad. 
