VOL. XXXI.] PHILOSOPHICAL TRANSACTIONS. 53Q 



it has been too hastily concluded, that these stones are very improperly called 

 by that name, as not at all approaching to the specific gravity of even the 

 lightest real stones. 



Whereas it is much more reasonable to suppose, that those stones, which 

 have been found to be so light, were such as had been a considerable time taken 

 out of the bladder, and consequently had lost much of their weight by the 

 evaporation of the urine, with which they had at first been saturated, and that 

 they had afterwards been tried without the caution above-mentioned. I would 

 therefore beg leave to recommend it to those who shall examine the specific 

 grnvity of the human calculus, that they will either try the experiment on stones 

 fresh taken out of the bladder, or else to use the abovesaid method, to extricate 

 the air out of their cavities. By doing this, I am confident they will meet with 

 some calculi, as I have done, exceeding the weight of some sorts of burnt 

 earthen-ware and alabaster, and approaching very near to that of brick, and 

 the softer kind of paving stone. But it is not to be expected, that they should 

 quite equal the specific gravity of stone found in the earth ; because the mix- 

 ture of some portion of the animal oil and volatile salt, with the stony sub- 

 stance of the human calculi, must needs lessen the specific gravity of the whole 

 concrete. 



I shall mention one other observation relating to this subject; which, how- 

 ever trivial it may seem, yet to me was very surprising, when I accidentally 

 discovered it : viz. that the substance of all wood, as oak, fir, &c. is specifically 

 heavier than water. To prevent being misunderstood, I must observe, that in 

 wood and other vegetables, there are two sorts of vessels, one of which convey 

 the sap, and the other contain only air, for which reason they are called air- 

 vessels. When wood floats, or swims in water, this effect is not owing to the 

 lightness of the substance of the wood, but only to its being buoyed up by the 

 air contained in those vessels. For when the air is extracted out of them, and 

 the water has insinuated itself in their stead, the wood will sink to the bottom. 

 As is very easily shown in small chips, or shavings of wood, by means of the 

 air-pump, or an infusion in boiling, or even in cold water for a sufficient time. 

 And the same is found to succeed in the roots, stalks, leaves, and seeds of as 

 many other vegetables as I have yet tried ; cork only excepted ; in which last I 

 had no reason to expect it, considering the particular structure of that sub- 

 stance, as described by Dr. Hook, in his Micrographia. 



Of an Ossification of the Crural Artery. By Mr. Edward Naishj Surgeon, 



York. N° 369, p. 226. 



Mr. Consett, of Cleveland, Yorkshire, 67 years of age, who had all his life 



3z 2 



