56 Analyses of Books. [Jan. 



with very little variation, their primary form, and did not con- 

 tract more than 3-| per cent, in drying." 



Mr. Knight's second experiment consisted in taking a trans- 

 verse section, of about an inch in thickness, from the stem of a 

 tree that was just felled. An incision was then made with a 

 saw from the bark towards the central medulla, in the direction 

 of the convergent cellular processes, when they were found 

 almost entirely to prevent the action of the saw in consequence 

 of their expansion ; and when a second incision was made from 

 the bark to the medulla, about an inch from the first, leaving a 

 triangular wedge, the expansion of the silver grain kept the 

 piece closely retained in the stem. When incisions were made 

 in the other part of the block, but in such a direction as to cut. 

 the processes across, the saw was found to move with perfect 

 freedom. From these facts the author was led to infer that the 

 medullary canal must be subject to have its diameter consider- 

 ably affected by variations in the quantity of moisture contained 

 in the wood ; and this conjecture seemed to be confirmed by an 

 experiment, in which a plug of metal forced into the central 

 space, which had been occupied by the medulla of a young 

 stem, while this was in a dry state, was found too small to fill 

 the cavity, when the stem was saturated with moisture. Mr. 

 Tonight conceives that the internal clefts which are frequently 

 met with in timber may be produced by this kind of expansion 

 and contraction ; a cause which he conceives more likely to 

 operate than either winds or frosts, to which they have generally 

 been attributed. Another cause by which timber becomes 

 warped in drying is pointed out, which has probably no con- 

 nexion with the power by which the sap is raised in the living- 

 tree, but which arises from the greater br less solidity of the 

 different parts of the trunk, according as they are nearer or 

 more remote from the centre, the former being more compact, 

 and of greater specific gravity, and therefore being less affected 

 by the evaporation of its moisture. 



Dr. Davy's observations, which were made during his voyage 

 to Ceylon, were principally confined to three topics : " the spe- 

 cific gravity of the water of the ocean, and its temperature, and 

 the temperature of the atmosphere." He first presents his 

 principal results in the form of a table, and he afterwards in- 

 forms us how they were obtained, and offers various remarks 

 concerning them. The table consists of 13 columns : the first 

 contains the date ; the second, the latitude by obsei~vation ; the 

 third, the longitude by the chronometer ; the fourth is the spe- 

 cific gravity of the sea water ; the three next columns relate to 

 the temperature of the air, its maximum in the course of the 24 

 hours, its minimum, and its mean ; the next three columns give 

 us the maximum, the minimum, and the mean temperature oi 

 |he sea water; the 11th column contains the register of the 



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