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contracted, so producing a tension. The cloudiness in amber was due, therefore, 
to the intimate and irregular mixture of air or some gas, or even vacuities, with 
it ; other examples of the same law of light were seen in pounded rock-salt, or 
the powder of any transparent solid, clouds, condensed steam, foam, &c. Animi 
very rarely presented this appearance, nor was it probable that any amount of age 
would produce it. The greater number of these cavities were spherical, usually 
less than 1 4000th of an inch diameter, and sometimes occurred in waves, but 
occasionally some were met with more or less resembling in shape a balloon with 
car attached. The minute structure of these was described, and a comparison 
instituted with cavities in the diamond, quartz, mellite, and other mineral sub- 
stances. Reference was then made to the organic remains, as insects, &c, found 
in amber, the action of chloroform on it described, and the paper concluded with 
the inference that amber had remained in a viscous state longer than recent resins, 
and that some specimens under different circumstances were in that condition much 
longer than others. 
The paper was illustrated with several beautiful specimens of animi 
and amber, and with drawings by Mr. Ravis of some of the microscopic 
appearances. Mr. C. O. G. Napier also sent specimens of amber from 
Fezzan, in North Africa, where they were used as money, as well as some 
picked up on the beach at Margate, which contained insects. 
The President, in thanking Mr. Butler for his paper, and Mr. 
Ravis for reading it, observed that though the cause and nature of these 
cavities were obscure, he questioned whether they had any relation to the 
cavities and vacuities in quartz ; similar ones were found in granite, and 
many of them contained water. He also explained that the submerged 
forests from which the Baltic amber was derived belonged to the Tertiary 
period. 
Mr. Leipner believed, on various grounds, that the cars attached to 
the balloon-shaped cavities were probably vacuities — the spherical cavities 
containing a gas or fluid. 
Mr. W. L. Carpenter spoke of the vacuities frequently met with in 
ice, as described by Prof. Tyndall, as well as of the constant presence of 
air, which was entangled in it, both of which causes rendered it opaque. 
He also drew attention to the opacity in many specimens of ordinary 
resin, caused by the intimate mixture of turpentine, which could be 
expelled by heat, and the resin made clear. As little as 1 per cent, of tur- 
pentine equally diffused through the mass, produced this effect. 
Mr. W. W. Stoddart described the production of balloon-shaped cavi- 
ties in Canada balsam (also a resin) when heated on a glass slide for 
mounting microscopic objects. 
Mr. C. O. Groom-Napier's paper on "The Analogy between the 
Horse and Man," which was announced for this evening, was postponed 
till the April meeting, to enable the author to be present, and to read it 
himself. 
c 
