6 REPORT—1852. 
aperture, are completely corrected, and no attempt even is made to remove the 
influence of the secondary spectrum. With small apertures, too, objects, or 
parts of objects, at different distances, will be delineated with nearly the same 
distinctness, and a picture produced as nearly resembling the original as it can be 
made in the present state of practical optics, 
The same observations, with the exception of those which relate to the achromatism 
and the thickness of the refracting medium, are applicable to the images produced 
by mirrors of different sizes. 

On the Stereoscopometer. By A. CLAUDET. 
This was a simple instrument, by which the relative positions of the two cameras 
and the placing of the object could be accurately determined in taking the pictures 
for the binocular stereoscope. 
—_- —__ 
On a Manifold Binocular Camera, By A. CLaupeEt. 
The author exhibited a Double Camera for taking the two stereoscopic Daguerreo- 
types of groups or individuals, and by which four double pictures could be succes- 
sively taken with such rapidity as to be exact representations of the same circum- 
stances. It would be impossible to make all the mechanical arrangements of this 
instrument intelligible without drawings. 
7 
On the Laws of Magnetism and Diamagnetism, in a Letter to Dr, Faraday. 
By Professor Marrevect. 
Pisa, August 15, 1852. 
My pear Farapay,—With much regret, and at the last moment, I am compelled 
to renounce the pleasure of assisting at the Meeting of the British Association and 
of conversing with you and other friends on scientific subjects. I beg you to present 
my cordial thanks to Col. Sabine for the invitation he so kindly sent me. I ask 
your permission to address to you an evtract of my researches on magnetism and 
diamagnetism, which have occupied me for several years: if you think that this 
communication can offer any interest to the members of the Association, you can, if 
you please, read it to the meeting, as I should be glad in any way to prove my 
gratitude to that respectable body. ; 
I have studied, in the first place, the influence of temperature and mechanic action 
on magnetic and diamagnetic substances. Thus, I operated on iron in a state of 
fusion obtained by the flame of oxyhydrogen gas. In this experiment a small iron 
globule is placed in a cavity at the extremity of a horizontal bar of copper wire or 
caustic lime, suspended by a cocoon silk in the magnetic field between the conical 
poles of a very powerful electro-magnet. Iron in a state of fusion, partially oxidated, 
is always attracted by the magnet; the diminution of magnetic attraction produced 
by fusion in iron is immensely great: in one experiment, which I think was suf- 
ficiently exact, I found that attraction became at least 15 million times less, passing 
from the ordinary temperature to the state of fusion. All the compounds of iron, 
and all natural substances containing a portion of metallic iron, suffer a diminution 
by heat; hence it is that the natural or artificial compounds of magnetic and dia- 
magnetic substances, such as certain coals and charcoal, clay, impure metals, gold, 
copper, zine, &c., which are attracted at the ordinary temperature, appear to be 
temporarily repelled when strongly heated. Passing to diamagnetic substances, I 
have found that their repulsive action suffers a very slight diminution by fusion in 
phosphorus and sulphur. But this is not the case with bismuth in fusion, upon 
which I have verified and completed the observation of Pliicker. 
The following experiment is simple, and sure to succeed at the first attempt. Take 
a bar of pure caustic lime and suspend it in the magnetic field in the manner 
deseribed ; when the magnetic power is developed, the bar is repelled ; and when 
the bar is strongly heated, the repulsion is certainly not less great. Touching lightly 

