530 
POLARIZING STRUCTURE OF THE LENS. 
of bismuth, nitrate of lead, superacetate 
of lead, subacetate of lead, distilled 
water the same as that in which the 
solutions were made. Of these the re- 
fractive indices of many were very high, 
and most of them of such a nature as to 
render them scarcely possible to be re- 
duced to the proper form. In conclu- 
sion he stated, that many crystals of 
various kinds of substance, if got pure 
would be invaluable for aiding in these 
researches — he particularized lead. The 
learned gentleman concluded by some 
notice of the researches of Dovey. 
Sir David Brewster stated many mo- 
des in which some of the most perplex- 
in difficulties met with by Mr. Powell 
might be avoided. He stated, that he 
could render very imperfect crystals 
ayailableby covering up their imperfec- 
tions with China ink ; also, we under 
stood him to say, that sometimes he 
interposed silk ; but he universally suc- 
ceeded inmaking the dark lines visible, 
by using the triple oxalate of chromium 
and lead as an interpo'jing substance. 
He also remarked that it would be very 
important to note accurately, the angle 
which the ray or beam of light made 
with the edge of the refracting angle of 
the prism, and illustratedits importance. 
■ — Mr. Powell showed, that in the very 
construction of his apparatus this was 
provided for. — Prefessor Forbes bore 
testimony to the extreme simplicity of 
the apparatus, and its capability of ac- 
curate investigations. H e had only just 
come from Oxford, where he had, had 
the pleasure of seeing and examining 
it, and from his own experience he could 
say, that any one, at all accustomed to 
such experimenting, might be readily 
trained to use it. 4 
A paper was then read, contributed 
by Sir. D, Brewster, ‘On the Polarizing 
Structure of the Crystaline Lens of the 
Eyes of Animals after Death. ^ 
The eyes examined were those of oxen 
and sheep, the tendency of the lens to 
indurate was prevented by immersion 
in distilled water ; the polorazing struc- 
ture was then examined ; great changes 
were stated to take place in that struc- 
ture in the eyes of aged animals. From 
these investigations, the writer was led 
to the results that there is in the crystal- 
line lens a capability of being developed 
by the absorption of the aqueous hu- 
mour; that a perfect structure is not 
produced until the animal frame is com. 
pletely formed ; and that when it begins 
to decay, the lens changes both its den- 
sity and focal length, and sometimes 
degenerates into the disease termed hard 
and soft cateract. Sir. D. Brewster is 
led to entertain a hope, that these re- I 
searches may furnish a means of preven- 
ting or curing that alarming disease. 
The Rev. J. W. M’Gauley then read 
‘A series of Experiments in Electro- jll 
Magnetism, with reference to its appli- S 
cations as a Moving Power.’ ] 
Previously to the detail of the ex- ■ 
pcriraents on this subject, he thought it !j 
might be interesting to the Section to 
relate what he had done since the last 1 
Meeting of the Association, in the ap- 
plication of electro-magnetism to ma- .j 
chinery. He had intended, originally, 1) 
to have exhibited the improvements, ; 
but should content himself, for the pre- J 
sent, with the detail, rather than the j| 
exhibition. He was obliged to confess, j 
that he was the less anxious prema- | 
turely to publish results, since he found ij 
that the working model of last year, |j 
given to the section, undoubtedly with \ 
the intention of its future improvement, |j 
or the pursuance of experiments by other i| 
Members, had led’ on several occasions, j 
to the production of papers, and the I 
exhibition of models, by those from I 
it might not be expected — with a pre- I 
tension to originality, but with no !| 
change in the principle, and almost I 
in the details. ! 
The working model exhibited to the j 
Sections at the last Meeting of the 
Association must be acknowledged as a | 
proof, to some extent;, at least, of the 
applicability and the manageable- ji 
ness of electro-magnetism as a moving 1! 
power; but the question then remaining 
was, whether or not it was likely to be : 
applied to useful purposes ; for this, 
several things remained undone, ' 'j 
Powerful magnets were to be con- 
structed. The ordinary formation of | 
electro-magnets furnishes us, at best, ! 
with an apparatus clumsy in the 
extreme, and, as we shall see, of very j; 
limited power. This arises from the I 
very nature of an electro magnet ; for ' 
the lifting power may be very great, 
although the attracting power at a !■ 
small distance may be very trifling. 
There must be a limit, also, to the size 
of these magnets, for, if the mass of 
iron be too great for the helix, it is not 
saturated with magnetism, and the j 
