TRANSACTIONS. 
81 
dimensions on the needle of the compass , and the investigation 
of the law of the deviation at different distances, and with 
magnets of various sizes. With a pair of three-feet bar magnets, 
he was able to produce a very perceptible action on the com¬ 
pass, through a variety of intervening solid substances, at a 
distance of more than 61 feet; and to measure with tolerable 
precision various masses of solid rock of from 3 feet to more 
than 40 feet in thickness by the magnetic deviations. The 
phenomena now communicated to the Association, with their 
different important applications, were the results of original 
investigations and discoveries, accomplished, for the most part, 
within the last ten months. 
A paper by Dr. Brewster on the structure of the crystal¬ 
line lens in fishes, birds, reptiles, and quadrupeds, was read 
by the Secretary, and illustrated with drawings and models by 
the author. After giving an account of the previous observa¬ 
tions of Leeuwenhoek and others, the author explained the 
method in which he conducted his inquiries. The lenses of 
almost all animals are composed of distinct fibres, and when 
any of the laminae are removed, the surface appears fibrous or 
grooved. In large lenses, the direction of these lines may be 
easily traced by the microscope alone, but in many cases this 
is quite impracticable. In order to get rid of this difficulty, 
the author observed the image of a candle or bright luminous 
object, when reflected from a fresh surface of the lens, and he 
found this colourless image invariably accompanied by coloured 
images on each side, as in mother-of-pearl, and in Mr. Barton’s 
Iris ornaments. As the direction of the fibres is necessarily 
perpendicular to the line joining these coloured images, and as 
the distance of the coloured images varies inversely with the 
diameters of the fibres, Dr. Brewster was able to trace these 
fibres to their points of convergency or terminations, even 
when the fibres themselves were no longer visible. When the 
crystalline lens is dried, a furrowed impression of its surface 
may be taken upon wax, and the impression will, like that from 
mother-of-pearl, exhibit the same coloured images. 
By the process now described, Dr. Brewster has examined 
many hundreds of the lenses of animals brought from all 
parts of the world, and has found that there are five different 
modes in which the fibres are arranged, the same mode being 
invariably found in the same animal. These different arrange¬ 
ments of the fibres were illustrated by elegant drawings from 
the pencil of Dr. Greville, and by wooden models, which ex- 
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